Indian Patents
Title of Invention

CONTINUOUS POSITIONING APPARATUS AND METHODS
Abstract Improved apparatus and methods for non-invasively assessing one or more parameters associated with systems such as fluidic circulating systems (e.g., the circulatory system of a living organism). In a first aspect, an improved method of continuously measuring pressure from a compressible vessel is disclosed, wherein a substantially optimal level of compression for the vessel is achieved and maintained using dynamically applied dither perturbations (e.g., modulation) on the various axes associated with the vessel. In a second aspect, a an improved apparatus and method are provided for monitoring hemodyna- mic parameters, such as blood pressure, in a continuous and non-invas- ive manner while operating under a single unifying scheme. One variant of this scheme using a simulated annealing (SA) type approach to determining and maintaining an optimal operating state.
Full Text CONTINUOUS POSITIONING APPARATUS AND METHODS
Priority
This application claims priority to U.S. Patent Application Serial No.
filed contemporaneously herewith (May 14, 2007) of the same title,
which claims priority to U.S. Provisional Patent Application Serial No. 60/800,164 filed May
13,2006 of the same title, each of the foregoing incorporated herein by reference in its entirety.
Copyright
A portion of the disclosure of this patent document contains material that is subject to
copyright protection. The copyright owner has no objection to the facsimile reproduction by
anyone of the patent document or the patent disclosure, as it appears in the Patent and
Trademark Office patent files or records, but otherwise reserves all copyright rights
whatsoever.
Background of the Invention
1. Field of the Invention
This invention relates generally to methods and apparatus for monitoring parameters
associated with fluid systems, and specifically in one aspect to the non-invasive monitoring
of arterial blood pressure in a living subject.
2. Description of Related Technology
The accurate, continuous, non-invasive measurement of blood pressure has long been
sought by medical science. The availability of such measurement techniques would allow the
caregiver to continuously monitor a subject's blood pressure accurately and in repeatable
fashion without the use of invasive arterial catheters (commonly known as "A-lines") in any
number of settings including, for example, surgical operating rooms where continuous,
accurate indications of true blood pressure are often essential.
Several well known techniques have heretofore been used to non-invasively monitor
a subject's arterial blood pressure waveform, namely, auscultation, oscillometry, and
tonometry. Both the auscultation and oscillometry techniques use a standard inflatable arm
cuff that occludes the subject's peripheral (predominately brachial) artery. The auscultatory
technique determines the subject's systolic and diastolic pressures by monitoring certain
Korotkoff sounds that occur as the :uff is slowly deflated. The oscillometric technique, on

the other hand, determines these pressures, as well as the subject's mean pressure, by
measuring actual pressure changes that occur in the cuff as the cuff is deflated. Both
techniques determine pressure values only intermittently, because of the need to alternately
inflate and deflate the cuff, and they cannot replicate the subject's actual blood pressure
waveform. Thus, continuous, beat-to-beat blood pressure monitoring cannot be achieved
using these techniques.
Occlusive cuff instruments of the kind described briefly above have generally been
somewhat effective in sensing long-term trends in a subject's blood pressure. However, such
instruments generally have been ineffective in sensing short-term blood pressure variations,
which are of critical importance in many medical applications, including surgery.
The technique of arterial tonometry is also well known in the medical arts. According
to the theory of arterial tonometry, the pressure in a superficial artery with sufficient bony
support, such as the radial artery may be accurately recorded during an applanation sweep
when the transmural pressure equals zero. The term "applanation" refers to the process of
varying the pressure applied to the artery. An applanation sweep refers to a time period
during which pressure over the artery is varied from over-compression to under-compression
or vice versa. At the onset of a decreasing applanation sweep, the artery is over-compressed
into a "dog bone" shape, so that pressure pulses are not recorded. At the end of the sweep,
the artery is under-compressed, so that minimum amplitude pressure pulses are recorded.
Within the sweep, it is assumed that an applanation occurs during which the arterial wall
tension is parallel to the tonometer surface. Here, the arterial pressure is perpendicular to the
surface and is the only stress detected by the tonometer sensor. At this pressure, it is
assumed that the maximum peak-to-peak amplitude (the "maximum pulsatile") pressure
obtained corresponds to zero transmural pressure. Note that other measures analogous to
maximum pulsatile pressure, including maximum rate of change in pressure (i.e., maximum
dP/dT) can also be implemented.
One prior art device for implementing the tonometry technique includes a rigid array
of miniature pressure transducers that is applied against the tissue overlying a peripheral
artery, e.g., the radial artery. The transducers each directly sense the mechanical forces in the
underlying subject tissue, and each is sized to cover only a fraction of the underlying artery.
The array is urged against the tissue to applanate the underlying artery and thereby cause
beat-to-beat pressure variations within the artery to be coupled through the tissue to at least
some of the transducers. An array of different transducers is used to ensure that at least one
transducer is always over the artery, regardless of array position on the subject This type of
tonometer, however, is subject to several drawbacks. First, the array of discrete transducers

generally is not anatomically compatible with the continuous contours of the subject's tissue
overlying the artery being sensed. This can result in inaccuracies in the resulting transducer
signals. In addition, in some cases, this incompatibility can cause tissue injury and nerve
damage and can restrict blood flow to distal tissue.
Other prior art techniques have sought to more accurately place a single tonometric
sensor laterally above the artery, thereby more completely coupling the sensor to the
pressure variations within the artery. However, such systems may place the sensor at a
location where it is geometrically "centered" but not optimally positioned for signal
coupling, and further typically require comparatively frequent re-calibration or repositioning
due to movement of the subject during measurement.
Tonometry systems are also commonly quite sensitive to the orientation of the
pressure transducer on the subject being monitored. Specifically, such systems show
degradation in accuracy when the angular relationship between the transducer and the artery
is varied from an "optimal" incidence angle. This is an important consideration, since no
two measurements are likely to have the device placed or maintained at precisely the same
angle with respect to the artery. Many of the foregoing approaches similarly suffer from not
being able to maintain a constant angular relationship with the artery regardless of lateral
position, due in many cases to positioning mechanisms which are not adapted to account for
the anatomic features of the subject, such as curvature of the wrist surface.
Furthermore, compliance in various apparatus components (e.g., the strap and
actuator assembly) and the lack of soft padding surrounding the sensor which minimizes
edge effects may adversely impact the accuracy of tonometric systems to a significant extent.
One very significant limitation of prior art tonometry approaches relates to the
magnitude and location of the applied applanation pressure during varying conditions of
patient motion, position, mean pressure changes, respiration, etc. Specifically, even when the
optimum level of arterial compression at the optimal coupling location is initially achieved,
there is commonly real-world or clinical factors beyond reasonable control that can introduce
significant error into the measurement process, especially over extended periods of time. For
example, the subject being monitored may voluntarily or involuntarily move, thereby
altering (for at least a period of time) the physical relationship between the tonometric sensor
and die subject's tissue/blood vessel. Similarly, bumping or jarring of the subject or the
tonometric measurement apparatus can easily occur, thereby again altering the physical
relationship between the sensor and subject. The simple effect of gravity can, under certain
circumstances, cause the relative positions of the sensor and subject blood vessel to alter
with time as well.

Furthermore, physiologic responses of the subject (including, for example, relaxation
of the walls of the blood vessel clue to anesthesia or pharmacological agents) can produce the
need for changes in the applanation level (and sometimes even the lateral/proximal position
of the sensor) in order to maintain optimal sensor coupling. Additionally, due to the
compliance of surrounding tissue and possibly measurement system, the applanation level
often needs to adjust with changes in mean arterial pressure.
Several approaches have heretofore been disclosed in attempts to address the
foregoing limitations. In one prior art approach, an occlusive cuff is used to provide a basis
for periodic calibration; if the measured pressure changes a "significant" amount or a
determined time has elapsed, then the system performs a cuff calibration to assist in resetting
the applanation position. Reliable pressure data is not displayed or otherwise available
during these calibration periods. See for example U.S. Patent 5,261,414 to Aung, et al issued
November 16, 1993 and entitled "Blood-Pressure Monitor Apparatus," assigned to Colin
Corporation (hereinafter "Aung"). See also U.S. Patent 6,322,516 issued November 27,2001
and entitled "Blood-Pressure Monitor Apparatus," also assigned to Colin Corporation,
wherein an occlusive cuff is used as the basis for calibration of a plurality of light sensors.
In another prior art approach, a pressure cuff or a pelotte equipped with a
plethysmographic gauge, such as an impedance or a photo-electric device, is used to drive a
servo control loop. See, e.g., U.S. Patent 4,869,261 to Penaz issued September 26, 1989 and
entitled "Automatic noninvasive blood pressure monitor," assigned to University J.E. Purkyne
v Brne (hereinafter "Penaz"). In this device, the sensor is connected through at least one
amplifier and a phase corrector to an electro-pressure transducer. All these components
constitute the closed loop of a servo control system which (at least ostensibly) continuously
changes the pressure in the cuff and attempts to maintain the volume of the artery at a value
corresponding to zero tension across the arterial wall. The servo control system loop further
includes a pressure vibration generator, the frequency of vibration being higher than that of the
highest harmonic component of blood pressure wave. A correction circuit is also provided, the
input of which is connected to the plethysmographic sensor and output of which is provided to
correct the setpoint of the servo control system. The Penaz system therefore in effect constantly
"servos" (within a cardiac cycle) to a fixed light signal level received from the sensor. Unlike
the Colin systems described above, the system continuously displays pressure to the operator.
However, the operation of the plethysmographic sensor of Penaz limited the application of this
device to a peripheral section of a limb (preferably a finger) where the peripheral pressure,
especially under conditions of compromised peripheral circulation, may not accurately reflect
aortic or brachial artery pressure. This presents a potentially significant cause of error.

Yet another prior art approach uses a series of varying pressure "sweeps" performed
successively to attempt to identify the actual intra-arterial blood pressure. The applanation
pressure applied during each of these sweeps is generally varied from a level of arterial
under-compression to over-compression (or vice-versa), and the system analyzes the data
obtained during each sweep to identify, e.g., the largest pressure waveform amplitude. See,
e.g., U.S. Patent 5,797,850 to Archibald, et al issued August 25, 1998 and entitled "Method
and apparatus for calculating blood pressure of an artery," assigned to Medwave, Inc.
(hereinafter "Archibald"). The system of Archibald is not truly continuous, however, since
the sweeps each require a finite; period of time to complete and analyze. In practice the
sweeps are repeated with minimal delay, one after another, throughout the operation of the
device. During applanation mechanism resetting and subsequent sweep operations, the
system is effectively "dead" to new data as it analyzes and displays the data obtained during
a previous sweep period. This is clearly disadvantageous from the standpoint that significant
portions of data are effectively lost, and the operator receives what amounts to only periodic
indications of the subject's blood pressure (i.e., one new pressure beat display every 15-40
seconds).
Lastly, the techniques for non-invasive pressure measurement disclosed by the
Assignee of the present invention in U.S. Patent No's. 6,228,034, 6,176,831, 5,964,711, and
5,848,970, each entitled "Apparatus and method for non-invasively monitoring a subject's
arterial blood pressure" and incorporated herein by reference in their entirety, include
modulation of applanation level at, inter alia, frequencies higher than the heart rate (e.g.,
sinusoidal perturbation at 25 H2). Further, Assignee has determined over time that it is
desirable in certain circumstances to control the applanation level according to other
modulation schemes and/or frequencies, and/or which are not regular or deterministic in
nature, such as those disclosed by co-owned U.S. Patent No. 6,974,419, entitled "Method
and apparatus for control of non-invasive parameter measurements" and incorporated herein
by reference in its entirety. Each of the foregoing methods, however, distinguishes between
two modes of operation, the first being (1) calibration; and the second being known as (2)
patient monitoring mode ("PMM").
"Simulated Annealing "
Simulated annealing (SA) is a term that relates to optimization schema that are
related to or modeled generally after physical processes. For example, one branch of
simulated annealing theory is a generalization of a Monte Carlo method for examining the
equations of state and frozen states of n-body systems. The concept is based to some degree

on the manner in which liquids freeze or metals recrystalize during the physical process of
annealing. In an annealing process, material initially at high temperature and disordered, is
cooled so as to approximately maintain thermodynamic equilibrium. As cooling proceeds,
the system becomes more ordered and approaches a "frozen" ground state at Temperature
(T)=0. Accordingly, SA can be thought of as analogous to an adiabatic approach to the
lowest energy state. If the staning temperature of the system is too low, or the cooling
regimen is insufficiently slow, the system may form defects or freeze in meta-stable states;
i.e., become trapped in a local minimum energy state.
One scheme (Metropolis) selects an initial state of a thermodynamic system (energy
E and temperature T), and holding T constant, the initial configuration is perturbed, and the
change in energy (dE) determined. If the change in energy is negative, the new configuration
is accepted. If the change in energy is positive, it is accepted with a probability determined
by the Boltzmann factor exp-(dE/T). This processes is then repeated sufficient times to give
adequate sampling statistics for the current temperature. The temperature is then
decremented, and the entire process repeated until a "frozen" state is achieved (at T=0).
This Monte Carlo approach can be analogized to combinatorial problems. The
current state of the thermodynamic system is analogous to the current solution to the
problem. The energy equation for the thermodynamic system is analogous to the objective
function. The ground state is analogous to the global minimum.
A significant difficulty in implementing this algorithm, however, is that there is often
no obvious analogy for the temperature (T) with respect to a parameter in the combinatorial
problem. Furthermore, avoidance of entrainment in local minima (quenching) is dependent
on an "annealing schedule", the choice of initial temperature, the number of iterations
performed at each temperature, and how much the temperature is decremented at each step
as cooling proceeds.
Based on the foregoing, there is needed an improved apparatus and methodology for
accurately and continuously controlling the non-invasive measurement of parameters such as
pressure. Such improved methodology and apparatus would ideally integrate the highly
efficient simulated annealing (SA) approach and allow for, inter alia, continuous measurement
(tonometrically or otherwise) of one or more physiologic or hemodynamic parameters, the
measured values of such parameters being reflective of true (e.g., intra-arterial) parameters,
while also providing robustness and repeatability under varying environmental conditions
including motion artifact and other noise. In addition, such method and apparatus would operate
under a substantially unified scheme, as opposed to the two or more independent schemes
modeled in prior art devices.

Such a method and apparatus would also be easily utilized by trained medical personnel
and untrained individuals, thereby allowing subjects to accurately and reliably conduct self-
monitoring if desired.
Summary of the Invention
In a first aspect of the invention, transient-resistant apparatus for determining the blood
pressure of a living subject is disclosed. In one embodiment, this comprises a processor and a
computer program running on said processor, said program comprising at least one simulated
annealing related algorithm.
In a second aspect of the invention, a method of determining hemodynamic parameters
using a simulated annealing-based algorithm is disclosed.
In a third aspect of the invention, a computer storage medium comprising a computer
program adapted for substantially unified mode operation according to a simulated annealing
algorithm is disclosed.
In a fourth aspect of the invention, a method of maintaining a substantially optimal
level of compression for the vessel using dynamically applied dither perturbations on at least
one axes associated with the vessel is disclosed.
In a fifth aspect of the invention, a method of treating a living subject based on
simulated annealing techniques for assessing hemodynamic parameters) is disclosed.
In a sixth aspect of the invention, a method of compensating for transient events so as
to maintain a hemodynamic assessment process in a substantially optimal state is disclosed.
These and other features of the invention will become apparent from the following
description of the invention, taken in conjunction with the accompanying drawings.
Brief Description of the Drawings
Fig. 1 is a flow diagram illustrating the fundamental process steps performed in
accordance with one exemplary embodiment of the control methodology of the present
invention.
Fig. 2 is a flow diagram illustrating the operation of the exemplary embodiment of
the first (annealing entry) process of Fig. 1.
Fig. 2a is a graph illustrating starting system temperature as a function of initial pulse
pressure for one exemplary embodiment of the present invention.
Fig. 3 is a flow diagram illustrating the operation of one exemplary embodiment of
the second process (dither generation) of Fig. 1.

Fig. 3a is a flow diagram illustrating one exemplary process flow for determining the
next dither pair sequence and executing the dither pair of Pig. 3.
Fig. 3b is a flow diagram illustrating one exemplary process flow for generating,
transforming and baking a unit dither according to one embodiment of the present invention.
Fig. 3c is a flow diagram illustrating one exemplary process flow for collecting beat
data in accordance with one embodiment of the present invention.
Fig. 3d is a graph illustrating the drawbacks of fixed applanation dither size as it
applies to slew-rate limiting in accordance with the principles of the present invention.
Fig. 3e is a graph illustrating the probability of an applanation-only dither as a
function of temperature in accordance with one embodiment of the present invention.
Fig. 3f is a graph illustrating the temperature coefficient as a function of temperature
in accordance with one embodiment of the present invention.
Fig. 3g is a graph illustrating temperature as a function of number of beats to collect
in accordance with one embodiment of the present invention.
Fig. 4 is a flow diagram illustrating the operation of one exemplary embodiment of
the third process (e.g. hemodynamic parameter processing) according to the invention.
Fig. 4a is a graph illustrating PMM bias as a function of mean pressure in accordance
with one embodiment of the present invention.
Fig. 4b is a graph illustrating PMM bias temperature factor as a function of
temperature in accordance with one embodiment of the present invention.
Fig. 4c is a graph illustrating delta energy as a function of delta pulse pressure in
accordance with the principles of the present invention.
Fig. 4d is a graph illustrating transition probabilities as a function of pulse pressure
and temperature in accordance with one embodiment of the present invention.
Fig. 5 is a flow diagram illustrating the operation of one exemplary embodiment of the
fourth process (e.g. adapting behavior of system) of Fig. 1.
Fig. Sa is a graph illustrating average mean as a function of temperature tax in
accordance with one embodiment of the present invention.
Fig. 6 is a block diagram of one exemplary embodiment of the apparatus for
hemodynamic parameter assessment within the blood vessel of a living subject according to the
invention.
Detailed Description of the Invention
Reference is now made to the drawings wherein like numerals refer to like parts
throughout.

It is noted that while the invention is described herein primarily in terms of a
apparatus and methods for the control of non-invasive measurements of hemodynamic
parameters such as blood pressure obtained via the radial artery (i.e., wrist) of a human
subject, the invention may also be readily embodied or adapted to monitor such parameters
at other blood vessels and locations on the human body, as well as monitoring these
parameters on other warm-blooded species. Similarly, the techniques of the present
invention can be applied to other parameters, as well as other similar fluidic systems which
have similar properties to those of the circulatory system of a living being. All such
adaptations and alternate embodiments are readily implemented by those of ordinary skill in
the relevant arts, and are considered to fall within the scope of the claims appended hereto.
As used herein, the term "continuous" is meant to include without limitation
continuous, piece-wise continuous, and/or substantially continuous processes (e.g., those
which are generally continuous in nature, but are not perse continuous).
As used herein, the term "hemodynamic parameter" is meant to include parameters
associated with the circulatory system of the subject, including for example pressure (e.g.,
diastolic, systolic, pulse, or mean pressure), derivatives or combinations thereof, arterial
flow, arterial wall diameter (and its derivatives), cross sectional area of the artery, and
arterial compliance.
Additionally, it is noted that the terms "tonometric," "tonometer," and "tonometry"
as used herein are intended to broadly refer to non-invasive surface measurement of one or
more hemodynamic parameters, such as by placing a sensor in communication with the
surface of the skin, although contact with the skin need not be direct, and can be indirect
(e.g., such as through a coupling medium or other interface).
The terms "applanate" and "applanation" as used herein refer to, without limitation,
the compression (relative to a state of non-compression) of tissue, blood vessel(s), and other
structures such as tendon or muscle of the subject's physiology. Similarly, an applanation
"sweep" refers to one or more periods of time during which the applanation level is varied
(either increasingly, decreasingly, or any combination thereof). Although generally used in
the context of linear (constant velocity) position variations, the term "applanation" as used
herein may conceivably take on any variety of other forms, including without limitation (i) a
continuous non-linear (e.g., logarithmic) increasing or decreasing compression over time; (ii)
a non-continuous or piece-wise continuous linear or non-linear compression; (iii) alternating
compression and relaxation; (iv) sinusoidal or triangular waves functions; (v) random motion
(such as a "random walk"; or (vi) a deterministic profile. All such forms are considered to
be encompassed by these terms.

As used herein, the terns "epoch" refers to any increment of time, ranging in duration
from the smallest measurable fraction of a second to more than one second.
As used herein, the terms "spatial" and "position", although described in terms of a
substantially Cartesian coordinate system having applanation (i.e., Z-axis), lateral (X-axis)
and (Proximal refers to closer to the heart) longitudinal or (proximal—distal) (Y-axis)
components, shall refer to any spatial coordinate system including, without limitation,
cylindrical, spherical, and polar. Such use of alternate coordinate systems may clearly be
independent of any particular hardware configuration or geometry (e.g., by performing
simple mathematical translations between a Cartesian-based apparatus and the non-Cartesian
coordinate system), or alternatively make advantageous use of such geometries. The present
invention is therefore in no way limited to certain coordinate systems of apparatus
configurations. As one example, it will be recognized that the methods and apparatus of the
present invention may be embodied using a cylindrical coordinate system modeled around
the radial artery, such that a particular point in space for the tonometric sensor(s) can be
specified by the Z, r, and 6 parameters. This approach may have advantages since the
forearm/wrist area of the human being very roughly comprises a cylindrical form.
As used herein, the term "temperature" refers to, without limitation, any parameter
which can be correlated or analogized to temperature in an actual or physical annealing process
including, for example, confidence level. Temperature as used in the context of the SA models
disclosed herein is merely an aostract concept representative of a quantity or property
associated with the system being controlled or modeled.
As used herein, the term "application" (in the context of a software application)
refers generally to a unit of executable software that implements a certain functionality or
theme. The themes of applications vary broadly across any number of disciplines and
functions (such as on-demand content management, e-commerce transactions, brokerage
transactions, home entertainment, calculator etc.), and one application may have more than
one theme. The unit of executable software generally runs in a predetermined environment;
for example, the unit could comprise a downloadable Java Xlet™ that runs within the
JavaTV™ environment.
As used herein, the term "computer program" or "software" is meant to include any
sequence or human or machine cognizable steps which perform a function. Such program
may be rendered in virtually any programming language or environment including, for
example, C/C++, Fortran, COBOL PASCAL,, assembly language, markup languages (e.g.,
HTML, SGML, XML, VoXML), and the like, as well as object-oriented environments such

as the Common Object Request Broker Architecture (CORBA), Java™ (including J2ME,
Java Beans, etc.) and the like.
As used herein, the term "integrated circuit (IC)" refers to any type of device having
any level of integration (including without limitation ULSI, VLSI, and LSI) and irrespective
of process or base materials (including, without limitation Si, SiGe, CMOS and GaAs). ICs
may include, for example, memory devices (e.g., DRAM, SRAM, DDRAM,
EEPROM/Flash, ROM), digital processors, SoC devices, FPGAs, ASICs, ADCs, DACs,
transceivers, memory controllers, and other devices, as well as any combinations thereof.
As used herein, the term "memory" includes any type of integrated circuit or other
storage device adapted for storing digital data including, without limitation, ROM. PROM,
EEPROM, DRAM, SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, "flash"
memory (e.g., NAND/NOR), and PSRAM.
As used herein, the terms processor,, "microprocessor" and "digital processor" are
meant generally to include all types of digital processing devices including, without
limitation, digital signal processors (DSPs), reduced instruction set computers (RISC),
general-purpose (CISC) processors, microprocessors, gate arrays (e.g., FPGAs), PLDs,
reconfigurable compute fabrics (RCFs), array processors, and application-specific integrated
circuits (ASICs). Such digital processors may be contained on a single unitary IC die, or
distributed across multiple components.
Overview
In one fundamental aspect, the present invention comprises apparatus and methods
for controlling an applanation or other positioning mechanism used in physiologic analysis
such as, e.g., non-invasive hemodynamic parameter measurements in order to, inter alia,
maintain optimal coupling between a parameter sensor and the blood vessel of interest.
These improved apparatus and methods are based on simulated annealing (SA) paradigms
that provide a substantially unified and highly effective means for placing and maintaining
the hemodynamic assessment or other such system in an optimized operational state.
Maintenance of this state correlates, inter alia, to the best possible accuracy for the
parameters) (e.g., blood pressure) being measured.
Exemplary techniques for determining the optimal applanation level, position, and
coupling that can be utilized with or benefit from the present invention are described in
detail in, e.g., co-owned U.S. Patent No. 6,730,038 entitled "Method And Apparatus For
Non-Invasively Measuring Hemodynamic Parameters Using Parametrics" issued May 4,
2004 and co-owned U.S. Patent No. 5,974,419 entitled "Method and Apparatus for Control

of Non-Invasive Parameter Measurements" issued December 13, 2005 each of which are
incorporated by reference herein in their entirety.
The improved techniques and apparatus of the present invention advantageously may
be used with a broad range of hardware configurations, including e.g., a single sensor (or
array of sensors) as described in detail herein and the aforementioned and incorporated co-
pending application, or in conjunction with literally any type of other apparatus adapted for
hemodynamic parameter measurement, including for example the devices described in co-
pending U.S. patent application Ser. Nos. 09/815,982 entitled "Method and Apparatus for the
Noninvasive Assessment of Hemodynamic Parameters Including Blood Vessel Location"
filed Mar. 22, 2001, and 09/815,080 entitled "Method and Apparatus for Assessing
Hemodynamic Parameters within the Circulatory System of a Living Subject" also filed Mar.
22, 2001, both of which are assigned to the assignee hereof and incorporated herein by
reference in their entirety. For example, an entirely tonometric pressure-based approach can
be used. Alternatively, ultrasound measurements of blood pressure via blood flow kinetic
energy or velocity can be used as a confirmatory technique for the tonometric pressure-based
approach. As another example, lateral positioning based on analysis of the acoustic signals
relating to vessel wall detection may be used in addition to (or in place of) the pressure-
based techniques described in the cited co-owned patents and patent applications.
Hence, the various aspects of the present invention are advantageously compatible
with a number of different physiologic and hemodynamic assessment techniques. It will also
be recognized that the techniques and apparatus described herein are in no way limited to
tonometric applications; rather, these features may be implemented even in e.g., occlusive
cuff or pellot-based systems.
While the techniques described in the aforementioned co-pending patent and patent
applications have been determined by Assignee to be highly effective, their robustness and
utility in practical (e.g., clinical) settings is enhanced through the addition of one or more of
the various aspects of the present invention. In the context of blood pressure measurement,
existing approaches to acquire and measure the patient's mean arterial blood pressure
focused on the compression of the patient's tissues at a location directly over their artery of
interest (e.g., the radial artery) such that the observed pulse pressure was maximized. It is at
this point of maximum pulse pressure that the pressure exerted on the compressed artery
equals the mean arterial pressure. Observance of the mean arterial pressure in an accurate
way was largely predicated on locating the artery correctly, and compressing the artery at an
appropriate level of applanation.

Under some such approaches, location of the artery was accomplished using two
discrete steps or phases. First during an initial calibration phase, a scan of a narrow portion
of an acquisition space is performed by making broad movements along both the lateral and
applanation axes. Second, during the second phase of operation, the applanation location is
fine tuned using a series of small experimental dithers around the current operating point
located during the calibration phase. In this way, the two phases of artery location and
applanation can be viewed as a "large signal experiment" followed by a "small signal
experiment".
While there normally is no sense that a large signal experiment is better or worse
than a small signal experiment, there are some issues introduced to the system under
measurement by implementing such an approach. First, the observed pulse pressure may not
only be a function of the actual position of the transducer with respect to the artery, but it
quite probably is also a function of the history of stresses placed upon the involved tissues
by the actuator. It would therefore be reasonable to expect that this historical effect may be
amplified with larger disturbances of the system seen during initial calibration.
Second, using two separate modes of operation assumes that the system (i.e. the
transducer, actuator and patient's tissues) will respond similarly during both large signal and
small signal experiments, in effect assuming the system behaves in a linear fashion.
However, the operating point located during the initial calibration phase and the operating
point located during the second phase may be two different "answers" that are only
appropriate to their own respective phases of operation. In systems where only small
adjustments are made to the applanation position and the lateral position subsequent to
calibration, such a two phase solution can be problematic as the operating point located
during calibration may not be the ideal operating point location for the second phase and the
control system can have a tendency to get stuck at a local, as opposed to global, maxima.
Therefore in accordance with one embodiment of the invention, a method and
apparatus are provided for monitoring hemodynamic parameters, such as blood pressure, in a
continuous and non-invasive manner while operating under a single unifying scheme. In a
sense, this approach acknowledges the fact that we are constantly calibrating, always
questioning whether or not we are at the patient's optimal operating point to measure the
hemodynamic parameter of interest. One. embodiment of the invention includes a
measurement apparatus for measuring various hemodynamic parameters associated with the
human body. In addition, a digital processor is disclosed for calculating various parameters
in response to the measured parameters. Additionally, the invention includes a method and

apparatus for controlling the location of the measurement in response to information
generated by the digital processor.
In accordance with a described embodiment of the hemodynamic system monitoring
apparatus, the hemodynamic system apparatus implements a "simulated annealing" process
which unifies measurements under a single scheme of operation. In one exemplary
embodiment of the simulated annealing process, dithers of varying sizes will be dynamically
applied to the system around a given operating point. The size of these dithers will be
correlated to a confidence analysis (e.g. so-called temperature measurement), such that larger
changes to dither will be applied when confidence is low while smaller more subtle changes
will' be used when confidence is high. This simulated annealing process will be more
resilient against being trapped by so-called local maxima over prior art techniques, as well as
being more resilient against varying topologies of hemodynamic parameter curves. This
approach also opens up the solution space to the maximum amount allowed by the physical
actuator implemented (i.e. by allowing for adjustment in the applanation, lateral and distal
axes either serially or in parallel) and by further allowing for dynamic adjustment of the
position of the transducer over the 'radial artery further improving the reliability and
robustness of these classes of ion-invasive hemodynamic parameter monitors. Further,
because the unifying scheme is largely a "small signal" approach, although not necessarily
so due to factors such as this aforementioned optimal positioning confidence level,
disruptions to the system causing inaccurate non-invasive readings are effectively
minimized.
Continuous Positioning Methodology
It will also be recognized mat while the process of the present invention is described
subsequently herein with respect to a tonometric pressure sensor or transducer, it can be
applied more generally to other signal domains including without limitation ultrasonics and
electromagnetic radiation (e.g., IR, X-ray, etc.).
Furthermore, it will be appreciated that while primarily described in the context of
the aforementioned tonometric apparatus (i.e., a tonometric pressure sensor which also acts
to provide varying levels of compression of the underlying tissue and blood vessel(s)), the
methodology of the present invention may be practiced using apparatus having separate
components which provide these functions. For example, the control of the pressure sensor
may be partly or completely decoupled from the applanation control system, such that the
level of applanation can be varied independently from the coupling of the active surface(s) of
the sensor. A detailed discussion of exemplary electronic and signal processing apparatus

used to support the operation of the processes described herein is provided with respect to
Fig. 6 below.
It will be recognized by those of ordinary skill that the logical processes of the
present invention may also be practiced entirely algorithmically (e.g., in software) and/or
firmware.
Fig. 1 is a flow chart illustrating the general control methodology performed to
determine, e.g., the hemodynamic parameters) (blood pressure, etc.) of a living subject in
accordance with one embodiment of the present invention. The overall process can be
thought of as constituting four (4) basic methodological steps. The first step 102 comprises
the step of entry into the "simulated annealing" process and the pre-requisite calculations for
the steps that follow. This first step 102 is described further in detail with regards to Fig. 2
and its accompanying disclosure
It will be appreciated that the term "simulated annealing" as used herein is merely
used as an analogy for sake of easier understanding of the concepts of the invention, and in
no way carries any specific connotation or meaning.
In step 104, the variation (e.g., dither) generation process is initiated. The set of
dither factors typically includes an applanation dither factor, a lateral dither factor and a
distal dither factor, corresponding to the applanation, lateral and distal axes respectively for
the measuring apparatus. The dither generation process is discussed further herein with
regards to Fig. 3 and its accompanying disclosure. Alternative embodiments of the invention
described herein may include more or less dither factors and/or axes of interest and
implementation would be readily apparent to one of ordinary skill given the present
disclosure herein.
Step 106 corresponds to the pressure signal processing methodology utilized with
regards to the present embodiment of the invention. This methodology is described in
further detail with and in part with regards to Fig. 4 and its accompanying disclosure.
In step 108, the system behavior is adjusted based on the aforementioned dither
generation and hemodynamic parameter processing steps. Generally speaking, as the
confidence level of being located at the optimal point decreases the dither factors utilized are
increased in order to allow for "larger" searches of the optimal positioning point, this
optimal point being the ideal location from which to obtain hemodynamic parameter
readings. Conversely, as the confidence level increases, the dither factor is decreased in
order to allow only "smaller" searches for the optimal point in order to obtain hemodynamic
parameter readings, while simultaneously minimizing adverse influences on the system as a

result of the non-invasive measurement This adaptive behavior is discussed further with
regards to Fig. 5 and its accompanying disclosure.
At this point, the process 100 may end or alternatively the process may continue by
performing a new measurement at 102 and repeating one or more of the aforementioned
processes. For purposes of simplicity and brevity, processes 102, 104, 106 and 108 will be
primarily discussed with regard's to only two axes of interest (i.e., applanation and lateral),
although it is recognized that more or less axes processing steps could be implemented
consistent with the principles of the present invention.
(I) Simulated Annealing Entry
Referring now to Fig. 2, une exemplary embodiment of the simulated annealing entry
process 102 is shown. While the exemplary simulated annealing process is described in
conjunction with the use of tonometric blood pressure monitoring system, such as for
example the TL-150 developed and marketed by Tensys® Medical, Inc., the invention is in
no way so limited. In fact, the process discussed with regards to Fig. 2 may be utilized
within the framework of a plurality of different apparatus measuring other physiologic or
hemodynamic parameters, the aforementioned TL-150 merely being exemplary.
In step 202, a pressure transducer is applanated along the applanation axis at a
desired location; e.g., a palpation mark determined by a user, or location determined via
vessel location mechanism or technique such as ultrasound or the like. In a first
embodiment, the palpation mark is determined manually by first, palpating the radial styloid
process and then drawing a transverse line over this bone. Next, the location of the patient's
pulse is determined and the user will draw a line perpendicular to and intersecting the
transverse line previously drawn. The intersection of this line will be referred to herein as
the palpation mark. While discussed in terms of locating along the radial styloid process on
a patient's wrist, the palpation technique described herein could be equally applicable to
other areas of the human body, such as e.g. the ulnar pulse point, carotid pulse point, or
brachial pulse point, etc. The measuring apparatus is then placed over the palpation mark and
the pressure transducer will applanate the patient's tissue at the palpation mark to a specified
applanation pressure (such as e.g. 85 mm-Hg).
In step 204, it is determined whether the apparatus can detect pulse beats originating
from the pulse point (e.g., the radial pulse point palpation mark). If a pulse is detected, then
the apparatus will take an average of the pulse pressures observed over a specified number of
beats (e.g. four (4)), or employ another scheme for obtaining a desired data set at step 206,
and the process will then invoke the simulated annealing process with average pulse pressure

measurements at step 208. If the pulse is not detected, then a "hybrid" lateral process step is
invoiced at step 205.
Assuming that a pulse beat has not been detected, the hybrid lateral processing step is
invoked at step 205. Here, the apparatus will begin looking for beats by performing a lateral
scan beginning at a point that is a specified distance from the beginning of possible lateral
travel. It has been found through experiment that the specified distance of travel from the
beginning of possible lateral travel is often most effective at approximately 1/4 of an inch
(0.25 in.), although more or less travel clearly may be utilized.
Next, the apparatus will 'servo" (i.e., continuously or semi-continuously vary) the
applanation position in order to maintain an average pressure at a specified position such as
e.g. 60 mm-Hg. During the lateral scan, any beats collected by the apparatus are noted along
with the position and pressure reading of the sensor at the time of detection.
At this point in the hybrid lateral process, the apparatus determines whether it has
collected a predetermined number of beats (e.g. four (4) in the illustrated embodiment), or
has reached the end of lateral travel without detecting the required number of beats. If the
end of the specified lateral travel has been reached without detecting the specified number of
beats, step 205 is repeated; however this time a lower lateral scan velocity is used, and/or the
possible lateral travel area is increased.
On the other hand, if the predetermined number of beats had been collected, the
transducer will be positioned over the lateral position as indicated by the largest reading of
the collected beats. At the point, the apparatus will servo the applanation position of the
transducer until an average desired pressure (e.g., 85 mm-Hg) is reached, and collect another
predetermined number of beats in step 207.
In step 207, if it is determined the hybrid lateral process of step 205 was entered into
as a result of a motion recovery process; then the number of beats collected will be specified
at a number such as e.g. twenty (20) collected beats. If not a result of a motion recovery
process, a fewer number of collected beats is needed, such as e.g. four (4) beats. The
apparatus will then either query whether the required number of beats have been collected in
a specified time limit, and if the apparatus returns "true" to this inquiry, the apparatus will
average the pulse pressure measurements collected over the collected number of beats and
invoke step 208, the simulated annealing process.
If the apparatus times out prior to collecting the specified number of beats, then the
hybrid lateral process will repeat, but with a lower scan velocity. If this repeated hybrid
lateral process is repeated over a predetermined number of times (e.g. two (2)), then the user

will be notified of the processing error, and the process will be terminated or a diagnostic or
troubleshooting mode entered if desired.
In step 208, the simulated annealing process is invoiced tointer alia prepare for entry
into subsequent dither generation processing steps, as described further below with regards
to Fig. 3 and its accompanying disclosure. A starting temperature value is selected in step
208 using the chart of Pig. 2a showing starting temperature as a function of initial pulse
pressure. Fig. 2a demonstrates the functional relationship between starting temperature
(relative units) selected versus initial pulse pressure (in mm-Hg). For purposes of hardware
simplicity, a 1-D interpolator may be used to perform a piece-wise linear interpolation of the
starting temperature versus initial pulse pressure chart of Fig. 2a during step 208, although
more complex interpolations, or curve fitting algorithms are possible such as e.g. polynomial
or even spline interpolation.
(2) Dither Generation
Referring now to Fig. 3, one exemplary method for dither generation 104 is discussed
in detail. At a high level, the exemplary dither generation process 104 involves three basic
steps of operation: (1) determination of the next dither pair sequence 302; (2) execution of
the dither pair 316; and (3) clocking the temperature controller 350 according to a pre-
specifled scheme.
Regarding steps (1) and (2), i.e. dither pair determination and execution, these
processing steps will be discussed in detail below with regards to Figs. 3a, 3b and 3c.
Regarding step (3), logic within the apparatus will determine whether the
temperature controller has been decked a pre-specified (e.g. two (2)) number of times at step
352. If the logic returns "true", the current temperature will be reduced by by a prescribed
amount; e.g., one "click", at step 356. If the logic returns false, the current temperature will
be maintained at step 354.
Referring now to Fig. 3a, an exemplary embodiment of the process for determining
the next dither pair sequence 302 is described in detail. A dither pair sequence determines
the order of "experiments" or triais used when evaluating two different positions for the
transducer apparatus. A dither pair sequence can thus be thought of as the center, or "heart"
of the simulated annealing process that controls the positioning of the transducer under this
unifying scheme.
In the present embodiment, the dither pair sequence is substantially randomized. The
reasoning for this can perhaps best be explained by example. For instance, imagine that
activity with regards to the patient's pulse pressure is in reality uncorrected with the

apparatus movements. If this activity involves monotonic changes over large periods of
time, such as a result of a particular physiological or pharmacological effect, fixing the order
of the "experiments" or trials will have a very predictable and undesirable influence on the
test results. For example, in cases where the patient's pulse pressures are monotonically
increasing, and this increase is such that it is stronger than any influence exerted by moving
the transducer position, then whichever position tested last in the dither pair will usually
dominate, given that it will have the higher observed pulse pressure (as we are
monotonically increasing in pressure). In such a case the transducer position would almost
never move away from the previously established position. Conversely, if always ending
with the dithered position last in each dither pair, the transducer position would always tend
to move away with each dither pair to the randomly chosen dither. In order to combat this
effect, the order of the dither pair is randomized, effectively eliminating any long-term
accidental and non-causal correlation with external pulse pressure changes. Other schemes
may be used to avoid such effects as well, however, including those which specifically
analyze the possible effects (such as the foregoing monotonic scenario) and adaptively
develop a scheme which combats or mitigates such deleterious effects. Furthermore,
randomization may not be required at all times, and hence may be applied selectively if
desired.
As is known in the mathematical arts, randomizing of signals and/or numerical
sequences is most typically implemented through the use of so called pseudo random
number generators which generate Pseudo Random Binary Sequences (PRBS). Pseudo
Random Binary Sequences (PRRS) are a defined sequence of inputs (+/-1) that possess
correlative properties similar to white noise, but converge in within a give time period. In
addition, the inputs can be specified (and thereby optimized) to produce more effective
signal-to-noise ratio (SNR) within the constraints of the system. One common type of PRBS
sequence generator uses an n-bit shift register with a feedback structure containing modulo-2
adders (i.e. XOR gates) and connected to appropriate taps on the shift register. The generator
generates a maximal length binary sequence according to Eqn. 1:

The maximal length (or "m-sequunce") has nearly random properties that are particularly
useful in the present invention, and is classed as a pseudo-noise (PN) sequence. Properties of
m-sequences commonly include:

(a) "Balance" Property--For each period of the sequence, the number of '1's and '0's
differ by at most one. For example in a 63 bit sequence, there are 32 't's and 31 '0's.
(b) "Run Proportionality" Property-In the sequences of '1's and of'O's in each period,
one half the runs of each kind are of length one, one quarter are of length two, one
eighth are of length three, and so forth.
(c) "Shift and add" Property-The modulo-2 sum of an m-sequence and any cyclic
shift of the same sequence results in a third cyclic shift of the same sequence.
(d) "Correlation" Property—When a full period of the sequence is compared in term-
by-term fashion with any cyclic shift of itself, the number differences is equal to the
number of similarities plus one (1).
(e) "Spectral" Properties--The m-sequence is periodic, and therefore the spectrum
consists of a sequence of equally-spaced harmonics where the spacing is the
reciprocal of the period. With the exception of the dc harmonic, the magnitudes of
the harmonics are equal. Aside from the spectral lines, the frequency spectrum of a
maximum length sequence is similar to that of a random sequence.
In step 304, the apparatus will first determine whether in the previous dither pair, did
the apparatus both: (1) end with a dithered position; and (2) choose to go towards the dither.
In other words, was a new reference position established with the dithered position last. If
so, then step 306 is invoked. Conversely, if the answer is no, then step 308 is invoked.
Assuming for a moment, that the answer to the logical query of step 304 was yes,
then step 306 is invoked. At step 306, the apparatus queries to determine whether the
temperature (i.e. the starting temperature selected at step 208) is low enough to enable an
inferred reference position. An inferred reference position, as opposed to a standard
reference position, is a position that can be extrapolated upon a very specific circumstance.
This inferred reference position is extrapolated when a new dithered position is tested and
the apparatus, and the underlying algorithm, decides to go towards this new dithered
position.
A new reference position, at a predetermined distance between the two points beyond
the dithered position in a direction that is further away from the previous reference position

is "inferred". In one exemplary embodiment, this predetermined distance is 1/3rd (33.333%)
of the previous dither. This in effect exaggerates the original dither movement by an
additional l/3rd of the previous dither. However, such exaggerations are typically only
deployed at low temperatures to avoid excessive movements. At low temperatures this
extrapolation is desirable, as it provides a quantity of gain in order to increase slew rate
beyond that which a given dither size would otherwise imply.
Fig. 3d graphically demonstrates for the utility of the aforementioned concept.
Specifically, in cases where there is a fixed applanation dither size, small perturbations
cannot be tracked when they are small compared to the fixed applanation dither size.
Further, with large variations in the hemodynamic parameter measured, fixed applanation
dither sizes may have difficulty in keeping up (i.e. because they are typically slew-rate-
limited) with the signal. Therefore, as can be seen in Fig. 3d, it would be desirable to vary
the dither size as a function of confidence (i.e. by lowering dither size to measure small
perturbations when confidence is high and exaggerating dither size when confidence is low
as a result of large variations in the signal).
Referring back to step 306, if the temperatures are low enough to enable an inferred
reference position, then the apparatus will be asked to randomly choose between either of the
following possible dither sequences at step 310: (1) [inferred reference, dither]; or (2)
[dither, inferred reference]. Conversely, if the temperatures are not low enough, then the
apparatus will randomly choose between either of the following possible dither sequences at
step 312: (1) [reference, dither]; or (2) [dither, reference].
Referring back to the question queried back at step 304, if the answer to the query at
step 304 is negative, then the apparatus will invoke step 308. In step 308, the apparatus
queries to determine whether in the previous dither pair, did we both: (1) end with a
reference position; and (2) choose: to stay with the reference position (i.e. was a new position
not established and the reference position was last).
If the answer to the query at step 308 is negative, then the apparatus will randomly
choose between either of the following dither sequences at step 312 as previously discussed.
If the answer is in the affirmative, then the apparatus will choose randomly either
between (1) setting the dither sequence to [dither]; or (2) setting the dither sequence to
[reference, dither] at step 314. In the case of (1), since a new reference position was not
established in the previous dither pair and the reference position was last, processing time
can advantageously be spared by simply re-using the measurements from the immediately
prior measurement position.

Referring now to Fig. 3a. (part 2 of 3), one exemplary embodiment of the process for
executing the dither pair 316 is described in detail. At an abstract level, executing a dither
pair according to the present embodiment is equivalent to reading the specific dither
sequence previously determined and going to each specified position type in sequence. At
each position we collect the beat data then move on to the next position specified in the
sequence. At the conclusion of this iterative data collection enough data has been collected
to make a decision on which position should be declared as our reference position.
At step 318, the next position type specified in the sequence is first queried to
determine what position type it is. Depending on its position type, different algorithms or
processing steps may be implemented in order to process and execute the respective dither
pair. If the position type is an inferred reference position, then step 320 is invoked, while if
it is a reference position or dithered position, steps 322 or 324 are invoked, respectively.

At step 320, the position type has been determined to be an inferred reference
position by the apparatus. The reference position and the next target are set to a position that
is a predetermined value (e.g. 1/3rd) as far as the difference between the previous reference
position and the previous dithered position beyond the previous dithered position.
Mathematically, if our previous positions are designated PReference1-1 and PDither1-1 then the new
reference position PReference is computed as follows using Eqn. 2:

If the position type has been determined to be a reference position, then the apparatus will
set the target position to the current reference position at step 322.
If the position type has been determined to be a dithered position, then a dithered
position is generated at step 324, requiring the generation, transformation and "baking" of a
"unit dither" at step 326. The term "baking" refers in the present context to the process of
modifying the value of the unit dither as a function of temperature. At step 324, the
apparatus must first determine the axes that will be involved in the dither. These axes may
include, but are not limited to, the Cartesian axes previously discussed (i.e. applanation,
lateral, and distal axes). In one exemplary implementation, each dither can utilize
movements in any combination of the actuator axes (i.e., the aforementioned applanation,
lateral and distal axes) either serially or in parallel. The ability to move in more than one
axis in parallel can potentially speed up the response for cases where the pulse pressure
profiles are at steep angles with nespect to the principle axes. However, for pulse pressure

profiles that are largely parallel with the principle axes, single axis moves are often more
beneficial. It is believed that most of these profiles are largely parallel, but not exactly
parallel to, the principle axes. For purposes of robustness to alternate pulse pressure profiles,
while at the same time acknowledging the nominal tendency for the profiles to be largely
parallel to the exemplary actuator axes, a random mix of single and multiple axes dithers are
performed in the illustrated embodiment, whose distribution is statistically controlled as a
function of the current temperature.-
At step 328, and in one exemplary embodiment, a 1-D interpolator is used to perform
a piece-wise linear interpolation of the chart shown at Fig. 3e to determine the applanation
axis only dither probability. This exemplary chart shown in Fig. 3e is constructed currently
such that at high temperature values, the chart returns a value of 0.33, while at low
temperature values it returns a value of 0.66. Thus in this example, applanation-only dithers
are twice as probable at low temperature values, than at high temperature values. The
remaining dithers will be equally divided between performing a lateral-only dither, or a
combined applanation and lateral dither, etc. A substantially random number is generated in
the closed interval [0, 1]. This random number is then tested, if the random number is less
than the applanation-only probability, then only applanation will be involved in the next
dither. If the random number is greater than or equal to the applanation-only probability;
and is less than Eqn. 2, then only lateral movements will be involved in the next dither. If
the random number is greater than or equal to Eqn. 3, then both applanation and lateral
movements will be involved in the next dither.

Referring now to Fig. 3b, the unit dither is generated, transformed and "baked". A
unit dither is a unit less ordered N-Tuple of numbers, each of which is from the closed
interval [-1, 1], with N being the number of axes of movement implemented in the
exemplary actuator context This N-Tuple of numbers is central to the process for
generating randomized dithers for the simulated annealing algorithm described herein. For
purposes of simplicity, it is assumed that the number of axes (N) in the example of the
process of step 326 is equal to two (2), although more or less axes may be incorporated.
At step 330, the unit dither is generated. The apparatus first determines whether the
unit dither generation is for a reference dither. If the result returns "true", then a unit dither
of [0, 0] will be returned. If the result returns "false", then a randomly generated N-Tuple

that resides in a unit cube is generated. Unit dither generation is first started by generating a
random point within the unit cube. Although it is not desirable to end up with a unit sphere,
using a spherical coordinate system to generate the random point will allow for a distribution
of points such that most of the points wilt be concentrated at small radii. Random spherical
generation will distribute points in such a way that the number of points at a given radius is
nominally constant, thus this would imply lower densities at higher radii, as this constant
number of points will be distributed over a larger circumference at the larger radii. To avoid
this situation, random points aie first generated in a Cartesian coordinate system, in effect
guaranteeing a uniform distribution of points per unit volume.
Generating a randomly generated N-tuple is accomplished in one exemplary
embodiment in the following manner. These steps are repeated for each of the N
dimensions, here two (2), to generate the N-tuple.
First, a signed random number in the closed interval [-1, 1] is generated. Next, the
concept of offset bias is introduced. Adaptive and axis-specific offset biases, each of which
are constrained to values in the closed interval [-1, 1], are maintained to influence the
distribution of the randomly generated dithers. For example, a dither offset bias value of
zero in the illustrated embodiment indicates that there is no bias applied to the given dither
generation for a given axis, while a value of 1.0 indicates that 100% of the time a positive
going dither will be generated. Likewise a dither offset value bias of -1.0 indicates that
100% of the time a negative going dither will be generated. This concept is utilized to
adaptively respond to evidence developed that indicates, for example, that the majority of
successful dithers in the recent positioning history along the applanation axis were mostly
negative. In this case, a negative dither offset bias will be generated to increase the
likelihood of generating negative applanation dithers.
Using the current adaptively-determined offset bias for the given dimension i, Biasi,
Biasi is clipped to the closed interval of [-0.99, 0.99]. Bias is then calculated as being equal
to 1 minus Biasi. A random number R is generated in the closed interval [0, 1.0] and then a
signed random number is calculated using Eqn. 4.
SignedRcmdomNumber = 2 x R - Bias (Eqn. 4)
If SignedRandomNumber is greater than zero, then Eqn. 5 is used; if it is less than zero, Eqn.
6 is used. The ith component of the N-Tuple is set to the newly calculated
SignedRandomNumber.


The unit dither specification is then tested for compliance. The radius of the unit
dither is computed, and exemplary logic determines whether the radius of the unit dither is
less than or equal to one, to ensure that the point falls inside of the unit sphere. If the unit
dither falls within the unit sphere, then the logic determines if the radius is greater than or
equal to 0.5. This test is utilized to avoid the generation of small dithers relative to the
maximum possible given the current temperature.
If greater than or equal to 0.5, the square of the radius is calculated, while either
serially or in parallel a random number is generated in the closed interval [0, 1]. If the
random number generated is less than or equal to the square of the radius, then the unit
dither passes the criteria established and the result is returned. If any of these tests fail, unit
dither generation is repeated.
In step 332, the unit dither is transformed to a number with physical units to guide
the actuator movement. The transformation process converts this unit less N-tuple into a
similar N-tuple, but with physical units. Note, however, that the units may be different
depending on the axis that it controls. For instance applanation units in the transformed unit
dither may be in mm-Hg, although this is by no means a requirement, thus allowing for a
tissue compliance-related response further downstream in the apparatus code. Similarly
units for lateral position may use finer units than that used for distal position, to account for
differences in the potential range between these two axes. It is in this step that nominal
differences in travel, i.e. aspect ratio, between the various axes are taken into account.
First, for each axis in the N-tuple of the unit dither specification, the axis-specific
component in the N-tuple will be transformed. The maximum specified dither travel for the
given axis Dithermax will then be obtained. In one embodiment, this quantity will be fixed at
the compile time of the software implementing the algorithm, and will represent the nominal
maximum dither to be generated for the given axis, though run-time adaptations can cause
the generations of yet larger dithers when determined to be appropriate. The ith component of
the N-tuple is then transformed into physical units using Eqn. 7.


The adaptively determintsd aspect ratio is then applied. "Aspect ratio" as used in the
context of the present embodiment specifically refers to the aspect ratio between the
applanation and lateral and/or distal axes, etc., however for simplicity it will be only
discussed as the ratio between applanation and lateral. In this particular embodiment, this
more specifically refers to the ratio of the maximum applanation dither to the maximum
lateral dither (or derivative quantities relating thereto). At compile-time, a fixed nominal
aspect ratio is defined such that a given unit dither specification of [1, 1], the resulting dither
will have an applanation displacement versus a lateral displacement that are related by this
nominal aspect ratio. In other words, the nominal aspect ratio defined at compile-time
allows the code to abstract these nominal differences away, and therefore can largely
concentrate instead on the run-time tweaks to this basic relationship.
An aspect ratio "tweak" in the present context is an adaptively determined quantity
that is signed and has values in the closed interval [-1,1]. A value of "0" implies that no
adaptation is necessary in the dither aspect ratio. A positive value indicates that over-and-
above the nominal aspect ratio, applanation should be further emphasized, and a negative
value indicates that lateral should be further emphasized. In actual implementation when,
e.g., an applanation emphasis is tailed for, (i.e. an aspect ratio "tweak" > 0), "half of this
emphasis is placed upon the applanation axis, and "half of this is used to de-emphasize the
lateral axis. In this way, disruptions resulting from too large a degree the nominal vector
length of the dither being generated are advantageously avoided. If for instance, the
applanation axis has an aspect ratio tweak value that is positive, the applanation dither is
further emphasized. Note also that the use of "half of the aspect ratio tweak on the
applanation axis, and the other half on the lateral axis is meant purely in a geometric sense;
hence the use of the square root in Eqn. 8. The invention is in no way limited to such "half"
or other schemes, however. Conversely, if the applanation axis has an aspect ratio tweak
value that is negative, Eqn. 9 is used which effectively de-emphasizes further the applanation
dither.


An adaptively determined aspect ratio adjustment for pulse pressure curve asymmetry is then
applied. This is done in order to account for the typical pulse pressure curve asymmetries
found irrespective of whether the device is currently operating above or below the patient's
mean pressure. It has been found by the inventors hereof that pulse pressure slopes above
the patient's mean pressure roll-off at a much steeper rate than the pulse pressure rise below
the patient's mean pressure. In other words, when above the patient's mean pressure, there
is a need to de-emphasize the applanation axis dither, while this dither should be emphasized
when below the patient's mean pressure.
The adaptively determined dither offset values can be utilized to give an indication
whether or not the apparatus is largely applanating or de-applanating. If the apparatus is
largely applanating, then it can foe deduced that pulse pressure readings may be below the
patient's mean pressure. Conversely, if the apparatus is largely de-applanating, then it is
likely that the readings are above the patient's mean pressure. Through studies conducted by
the Assignee hereof, it has been determined that this ratio is roughly 260%; that is, the pulse
pressure slopes are approximately 2.6 times steeper above the patient's mean than below it.
Therefore, given AboveVsBelowMeanPPRatio = 2.60, the application ratio tweak is
calculated using Eqn. 10 where the AppOffset value is greater than or equal to zero,
otherwise Eqn. 11 is used.

Similarly, if it is desired to de-emphasize (using Eqn. 13) or emphasize (Eqn. 14) other axes,
such as the lateral axis, this can be calculated as well using similar aspect ratio tweaks.
Thus, the dither value at each position i is calculated using the value obtained by either Eqn.
10 or Eqn. 11 using Eqn. 12.




Following the transformation process of the unit dither, the unit dither is now
"baked" at step 334. The term "baking" refers in the present context to the process of
modifying the value of the unit dither as a function of temperature. It is generally expected
that a response at high temperatures (i.e. correlating to a lower confidence that the transducer
is located properly) the system should be displaced more, while at lower temperatures the
system is expected to be displaced less.
In one embodiment, the transformed unit dither is baked by first obtaining the current
"taxed" temperature for each axis. "Taxing", as the name implies, is the core system
temperature with an added "tax'; here a generic and arbitrary quantity that can be used for
multiple purposes. A tax can be applied to the temperature for various reasons, but in
general it is used to penalize the system, or perhaps put it in an increased state of
perturbation or awareness. In this embodiment, the temperature is taxed only when the
current mean pressure is particularly high or low (as determined against, e.g., predetermined
or variant criteria), corresponding to the likelihood that the value is not correct
It should also be noted that in the current embodiment, a temperature can be used
either taxed or not taxed and thus at any one time both versions can be made available in the
system. In an alternate embodiment, each axis will have a temperature equivalent to the
system-wide core temperature.
Referring now to Fig. 3f, the temperature coefficient is determined using a 1-D
interpolator to perform a piece-wise linear interpolation of the chart depicted in Fig. 3f. The
baked dither is then calculated using Eqn. 15.

Referring again back to Fig. 3a (part 3 of 3), in step 336 the apparatus advances to
the target position, regardless of whether it was an inferred reference position, reference
position or a dithered position. If the target position is not reached within a predetermined
amount of time (e.g. 1.5 seconds), then the system times out on this dither and notifies the
system while aborting the simulated annealing process.

If the target position is reached in time, the beat data is collected at step 338. The
process for collecting beat data is described in detail below with regards to Fig. 3c and its
accompanying disclosure.
After collection of the beat data, the system determines whether the last position was
the last position type in the sequence at step 346. If it is not, the whole process repeats
starting at step 318. If it is the last position in the sequence, the algorithm advances to
hemodynamic parameter processing.
(3) Hemodynamic Parameter Processing
Referring now to Fig. 3c, the collection of beat data 338 is described in detail. At step
340, the number of beats to collect is determined. In one embodiment, the number of beats
to collect is fixed at a predetermined number (e.g. two (2)). Alternatively, in a second
embodiment, the number of beats is collected as a function of one or more parameters (e.g.,
temperature). In this example, ti piece-wise linear interpolation of the chart of Fig. 3f
(Temperature vs. Beats to Collect) is used to determine the baseline number of beats to be
collected.
In a third embodiment that can be used either alone or in conjunction with either of
the two previous embodiments, (computer or algorithmic) logic determines whether the core
temperature value is below a certain threshold (e.g. 2000). If so, then a statistical algorithm
is employed which first generates a random number in the closed interval [0,1] and tests this
random number to see whether it it: either higher or lower than the midpoint of die interval
(i.e. 0.5). If it is less than the midpoint, a pre-specifted number of beats are added (e.g. one
(1)), while if the random number is greater than the midpoint, the number of beats to detect
is left at the existing value.
The reason for the foregoing approach utilized in this third embodiment is that at low
temperatures, there are conflicts between two opposing needs. As the vast majority of dithers
will occur at lower temperatures, the decisions made at these low temperatures would benefit
by as little noise as is practicable. On the other hand, it is undesirable to sacrifice a rapid
response to large changes, and to a large degree the noise is taken out in the long run as the
results of consecutive dithers that are cumulative in nature.
Furthermore it has been observed that at low temperatures, the resultant dithers of
these decisions are small in nature and that they therefore do not by themselves have a large
impact on these decisions. So in response, an approach is taken that statistically adds in the
equivalent of an additional "half a beat" on average at these low temperatures.

Therefore, at these lower temperatures, half of the time the number of beats are taken
as normally would be determined given the current temperature, etc., and the other half of
the time, one additional beat is taken under this third embodiment.
At step 342, beat detection is delayed for a predetermined amount of time. This beat
delay detection is utilized to account for delays such as (1) group delays in batch processing;
or (2) for settling time after a dither. In one embodiment, these delays are set to 250 ms and
125 ms respectively, accounting for a total delay of 375 ms, although it will be recognized
that other values may be used.
At step 344, the apparatus waits for either a beat timeout or a detected beat. A beat
timeout in the present context comprsies the absence of a detected beat during any
designated epoch of time, such as e.g., five (5) seconds. While primarily envisioned as only
utilizing a pre-established epoch of time, certain embodiments of the present invention may
extend, contract or adapt this timeout as conditions change within the system. For example,
after a detected motion event, the wait period may be reset, re-establishing the full
designated epoch of time. Alternatively, after a detected motion event, the wait period may
be extended for a specified period of time.
If on the other hand a beat is detected, the exemplary apparatus executes logic which
determines whether the detected beat occurred within a prescribed period (e.g., one second)
of a previously detected motion event. If it has, then the beat is ignored. If not, the beat is
stored for later processing. For example, in one embodiment, the detected beat is added to
previously detected beats to keep a running average calculation of mean pulse pressure
values over the duration of the beat collection cycle.
Referring now to Fig. 4, the hemodynamic parameter processing step 106 of Fig. 1 is
described in detail.
At step 400, patient monitoring mode (PMM) bias is applied to the measured pulse
pressure difference. PMM bias is a correction that is applied to the measured pulse
(pulsatile) pressure difference in order to correct what has been observed as flat pulse
pressure curves. It has been observed through experiment by the Assignee hereof that when
the pulse pressure versus mean pressure curves becomes flattened, the peak in this curve
occurs at a place that is actually higher than the patient's mean pressure. The flatter the
curve becomes, the larger this offset appears to be. As the peak in this pulse pressure curve
is used as a basis to determine the patient's mean pressure, a corrective bias is applied in
order to shift the peak towards lower pressure to correct for this phenomenon. This shift is
such that it will typically be larger for flatter curves, and smaller for sharper curves. In one
embodiment, this factor has been set to 35% (0.35). However, in order to avoid issues of

these bias values lowering pressures too far, various measures are taken to curtail its effect
In one exemplary embodiment, :he PMM bias in step 400 is applied as follows using Eqn. 16
and Eqn. 17:

After performing these two calculations, the PMM bias is determined by performing
a piece-wise linear interpolation of the reference mean as a function of PMM bias (chart
shown in Fig. 4a) to determine the nominal PMM bias to use. This linear interpolation can
be performed by using an interpolator (e.g. a 1-D interpolator). After obtaining the current
taxed (or in some embodiments, untaxed) temperature, a piece-wise linear interpolation of
the temperature as a function of PMM bias temperature factor is determined using a chart
such as that shown in Fig. 4b. The addition of the pulse pressure bias is then performed
thusly using Eqn. 18, Eqn. 19 and Eqn. 20:

Note that the term on the right side of Eqn. 19 is negative to reflect mat the higher the mean
pressure difference is, the more the pulse pressure difference should be de-emphasized.

Next, the algorithm must make the transition decision at step 402. This transition decision is
based on a combination of where the timeout occurred, and in which position (dithered
and/or reference). If no timeout occurred in either position (i.e. dithered and reference),
which is the most typical case, then pulse pressure change is determined using Eqn. 21 at
step 406.


At step 408, the transition probability is determined. In simulated annealing,
transition probabilities are based upon both the change in energy, (the negative of the change
in pulse pressure in one embodiment), and the current temperature. While the transition
probability is normally set to 100% if there is a decrease in energy, (simulated annealing
attempts to lower the total energy of a system; this is equivalent to an increase in pulse
pressure in the exemplary implementation for a hemodynamic system), there are a variety of
responses for the cases of no change in energy, or for an increase in energy state. This
feature in large part gives simulated annealing its inherent ability to be able to move away
from locally optimal areas and find what would be the global optima. In essence, it is the
ability to occasionally, in a metered way and under strict control, advance a move towards a
higher energy (lower pulse pressure) state, that provides many of the benefits of the
simulated annealing control process.
In step 408, the change in energy is determined using a piece-wise linear
interpolation of the AEnergy as a function of APressure (see chart of Fig. 4c). Note that the
chart and linear interpolation are only used for changes of pulse pressure that are negative.
If the AEnergy is negative, the transition probability is set to 1.0. If the AEnergy is equal to
zero, then the transition probability is set to 0.5. If the AEnergy is positive (i.e., the dithered
position resulted in a smaller pulse pressure) and the current temperature is greater than a
prescribed value (e.g., 500), then the transition probability is set to zero. However, if the
AEnergy is positive and the current temperature is less than 500, then a 2-D interpolator is
used to perform a bi-linear interpolation of the transition probability as a function of
temperature, and the delta energy chart of Fig. 4c is utilized to determine the transition
probability.
At step 410, if the timeout was only in the dithered position, or was in both the
reference and dithered positions, then the transition probability is set to zero. Conversely, at
step 412, if the timeout only occurs in the reference position, then the transition possibility is
set to 1.0.
At step 414, a decision is made about whether to take the transition or not In one
embodiment, the apparatus will generate a random number in the closed interval [0, 1]. If
the random number is less man the transition probability then the system will take the
transition towards the dithered position, otherwise it will start with the current reference
position.


Referring now to Fig. 5, an exemplary embodiment of the adaptive adjustment
algorithm of the invention is described.
Per step 500 the temperature is adaptively adjusted. Note that the exemplary
adjustments described herein are subject to limits beyond which the adjustment will not take
effect. For temperature increases, the limit imposes a maximum, and for temperature
decreases, the limit imposes a minimum. In adjusting the temperature, the timeout pattern is
also analyzed. In the nominal case (i.e. where mere is no timeout), signs of excessive
modulation of the pulse pressure are identified by determining whether or not there was a
large pressure change (step 502). In one exemplary embodiment, this determination is
accomplished in a two-step process. First, logic determines whether the large pulse pressure
is greater than a prescribed value (e.g., fifteen (15) mm-Hg). If not, the logic returns "false";
otherwise logic men queries whether the smaller pulse pressure is less than or equal to a
given percentage (e.g., 60%) of the larger pulse pressure. If it is, then the logic returns
"true", otherwise it returns "false". While the threshold limits of fifteen mm-Hg and 60% of
the larger pulse pressures have been chosen for this example, it is understood that these
numbers may vary considerably from application to application, the aforementioned
numbers merely being exemplary.
If the pressure change was too large in magnitude (i.e., the logic has returned true),
then the temperature is reduced (e.g. by a prescribed increment such as 2 "clicks") at step
504. If there was not a large instant pressure change, logic then determines whether or not
there was a large mean pressure change to determine whether the mean pressure is being
excessively modulated. In one embodiment, If the mean pressure change increases by more
than 35 mm-Hg, then the logic wilt return "true" and the temperature will be decreased by a
set amount (e.g. two (2) clicks). If not, then logic determines if there was too small of a
pulse pressure or mean pressure change at step 506. This is to ensure that at least a minimal
amount of both pulse pressure and mean pressure modulation is applied to the system.
In one variant, if the absolute pulse pressure change is less man 1 mm-Hg, then the
logic will return "true", otherwise it will determine if the absolute mean pressure change is
less than 1.5mm-Hg, and then return "true" if the answer is yes, otherwise it will return
"false". If logic determines the change was too small, then the temperature is increased at
step 510 (e.g. by 1.3 clicks), otherwise the temperature is kept current (step 508).
Note however that the aforementioned process (i.e. steps 502 - 510) are applicable
when there has been no timeout observed. At step 512, logic determines whether there was a
dither beat timeout, a reference beat timeout, or both. At step 514, the occurrence of a dither
beat timeout event normally suggests that the system may have been dithered too much so as

to lose the beat at the dithered position. This suggests a temperature that is too high if the
assumption that has been made is correct However, if the reference beat is not strong either,
then there is a risk of losing the reference beat as well by dithering too much, and inducing
too much large signal behavior.
Therefore, before assuming that the initial assumption was a valid one, logic is used
in the exemplary algorithm to determine whether the reference beat pulse pressure is greater
man a minimum amount (e.g. 10mm-Hg), which is to ensure that reducing temperature does
not raise the possibility that the reference beat may be lost by any large temperature changes
to the system. If the reference beat pulse pressure is greater than the minimum amount, then
the temperature is decreased. In one exemplary embodiment, the temperature is reduced by
three (3) clicks, otherwise no change is made.
At step 316, if there was only a reference beat timeout, then the temperature is
increased. In one embodiment, this temperature increase is 1.5 clicks, although other values
may be used.
At step 518, if there is both a reference and a dither beat timeout, then the
temperature is increased. In one embodiment, this temperature increase is by 2.5 clicks.
Note that in the illustrated embodiment, the temperature increase for this second condition
(both timeouts) is larger than for the reference-only timeout, since greater correction
magnitude is ostensibly required.
At step 519, respective dither strengths are determined given the dither specification.
Dither strength is a characterization of the degree to which a particular dither was deemed to
be either strongly lateral or strongly applanation, etc., or alternatively the degree to which it
was strongly neither. Recall that in general, random dithers have been taken along all of the
participating axes, however in order to tune various adaptive parameters it is often important
to collect data on the effectiveness of the dithers taken primarily along one of the principle
axes. In one embodiment, a strong predominantly signal-axis dither is taken to be one
whereby its normalized dither, equivalent to its mapping in the unit sphere, is within 30
degrees of a principle axis. In one exemplary embodiment, the dither strength is determined
as follows:
Step One: Normalize the applanation and lateral dither amounts using Eqn. 22;



Step Four: If yes to step three, then test Ditherapp>0. If yes, return
App_Is_Strongly_Positive, otherwise return App_Is_Strongly_Negative;
Step Five: If no to step three, then test the applanation dither amount using Eqn. 24

Step Six: If yes to step five, then test Ditherlot>0. If yes, return
Lat_Is_Strongly_Positivet otherwise return Lat_Is_Strongly_Negative; If no to step five, then
return neutral.
At step 520, a 12-point running sum for both applanation and lateral movements is
recorded.
It will be recognized that while the foregoing process is described with respect to
lateral and/or applantion axes or dimensions, others may be used, either in place of the
foregoing, or in conjunction therewith (or even in different permutations), as will be readily
implemented by those of ordinary skill given the present disclosure.
At step 522, the applanation and running sums for the adaptations are updated. In a
first embodiment, these sums are updated as follows.
If App_Is_Strongly_Positive is returned, then logic determines whether the transition
to the dither was taken. If yes, the applanation running sum is fed a value of two (2),
otherwise it is fed a value of negative one (-1).
If App_Is_Strongly_Negative. is returned, then logic determines whether the transition
to the dither was taken. If yes, the applanation running sum is fed a value of negative two (-
2), otherwise it is fed a value of one (I).
If Lat_Is_Strongly_Positive is retumed, then logic determines whether the transition
to the dither was taken. If yes, the lateral running sum is fed a value of two (2), otherwise it
is fed a value of negative one (-1).

If Lat_Is_Strongly_Negative is returned, then logic determines whether the transition
to the dither was taken. If yes, he lateral running sum is fed a value of negative two (-2),
otherwise it is fed a value of one (1).
If nothing is returned, notching is added to the running sums.
At step 524, the adaptive aspect ratio is determined. First, however, a similarity
score that measures how similar the applanation and lateral values are, a dissimilarity score
that determines how dissimilar the applanation and lateral values are and the categorization
strength score mat measures the extent to which the similarity and the dissimilarity scores
can be trusted needs to be determined. The equations for these calculations are shown below
as Eqn.'s (25) through (28).

Next, if the variable Scoreaolegqrbaalon snnslll > 0.35 then logic determines whether or
not Scoredtalmaarlv> Scoreslmllarlv If not, then the scores are said to be too unequivocal or
indefinite, and hence cannot be acted upon. In this case, the aspect ratio will be slowly
decayed towards zero, which is; generally the safest place to be whenever in doubt In one
embodiment, the aspect ratio is thus calculated using Eqn. 29:



this is an indication that the stores are probably similar. The aspect ratio should thus be
affected by the confidence of 1 similarity, however to be more careful, the aspect ratio is
approached geometrically rather than by making a sudden change to a new value. Recall that
our target aspect ratio for a similarity is simply towards zero. The aspect ratio is thus in one
embodiment calculated as:

indication that the scores are probably dissimilar. However, this is obviously easy to
conclude when one of the scores (e.g. applanation or lateral) is 0. So it must also be
demanded in that case a minimum absolute difference of scores (see e.g. Eqn. 31).

If Eqn. 31 is satisfied, then the likelihood of dissimilarity is more confidently reaffirmed.
However, the case where one of the scores (applanation or lateral) is zero has not been ruled
out. Since such a condition tends to exaggerate the dissimilarity score, when such a case
occurs it is desirable to modulate the dissimilarity score by the magnitude of the non-zero
score. See Eqn. 32.

If Scoreficdlotllstlty>Scoresimilarity, then the aspect ratio is calculated in one embodiment using
Eqn. 33, otherwise no action is taken.


At step 526, a temperature tax is adaptively assessed upon the reference mean. First,
the latest reference mean is added to an n-point (e.g. S-point) running average. In one
embodiment, the balance of these calculations occurs upon demand at the time that the taxed
temperature is required. This is particularly advantageous, as the tax is based upon the
current core temperature at the time that it is needed.
Next, a piece-wise linear interpolation is performed on an average mean as a function
of temperature tax chart as is shown in Fig. 5a. Upon determining the temperature tax, logic
determines if an "alternative minimum tax" (AMT) should be assessed. This AMT is
assessed when temperatures go below a certain threshold. This logic asks whether or not the
core temperature is below MaxTempForAMT? If so, then use Eqn. 34, otherwise the
apparatus uses Eqn. 35.

System Apparatus for Hemodynamic Assessment
Referring now to Fig. 6, exemplary embodiments of apparatus for measuring
hemodynamic properties within the blood vessel of a living subject consistent with the
control methodologies of the present invention are now described. In the illustrated
embodiment, the apparatus is adapted for the measurement of blood pressure within the
radial artery of a human being, although it will be recognized that other hemodynamic
parameters, monitoring sites, and even types of living organism may be utilized in
conjunction with the invention in its broadest sense.
The exemplary apparatus 600 of Fig. 6 fundamentally comprises an applanation
assembly (including one or more pressure transducers 622) for measuring blood pressure
from the radial artery tonometrically; a digital processor 608 operatively connected to the
pressure transducers) 622 (and a number of intermediary components) for (i) analyzing the
signals generated by the transducers); (ii) generating control signals for the stepper motor
606 (via a microcontroller 611a operatively coupled to the stepper motor control circuits);

and (iii) storing measured and analyzed data. The motor controllers 611, processor 608,
auxiliary board 623, and other components may be housed either locally to the applanator
602, or alternatively in a separate stand-alone housing configuration if desired. The pressure
transducer 622 and its associated storage device 652 are optionally made removable from the
applanator 602.
The pressure transducer 522 is, in the present embodiment, a strain beam transducer
element which generates an electrical signal in functional relationship (e.g., proportional) to
the pressure applied to its sensing surface, although other technologies may be used. The
analog pressure signals generated by the pressure transducer 622 are converted into a digital
form (using, e.g., an ADC 609) after being optionally low-pass filtered 613 and sent to the
signal processor 608 for analysis. Depending on the type of analysis employed, the signal
processor 608 utilizes its program either embedded or stored in an external storage device to
analyze the pressure signals and other related data (e.g., stepper motor position as
determined by the position encoder 677, scaling data contained in the transducer's EEPROM
652 via I2C1 signal).
As shown in Fig. 6, the apparatus 600 is also optionally equipped with a second
stepper motor 645 and associated controller 611b, the second motor 645 being adapted to
move the applanator assembly 602 laterally across the blood vessel (e.g., radial artery) of the
subject as described above. A third stepper motor (not shown) and associated controls may
also be implemented if desired to control the proximal positioning of the applanation
element 602. Operation of the lateral positioning motor 645 and its controller 611b is
substantially analogous to that of the applanation motor 606, consistent with the
methodologies previously described herein..
As previously discussed, continuous accurate noninvasive measurements of
hemodynamic parameters (e.g., blood pressure) are highly desirable. To this end, the
apparatus 600 is designed to (i) identify the proper level of applanation of the subject blood
vessel and associated tissue; (ii) continuously "servo" on this condition to maintain the blood
vessel/tissue properly biased for the best possible tonometric measurement; optionally; and
(iii) scale the tonometric measurement as needed to provide an accurate representation of
intravascular pressure to the user/operator.
During the simulated annealing process, the controller 611a controls the applanation
motor 606 to applanate the artery (and interposed tissue) according to a predetermined
profile. Such control schemes may also be employed with respect to the lateral and proximal
motor drive assemblies if desired, or alternatively a more static approach (i.e., position to an
optimal initial position, and then reposition only upon the occurrence of an event causing

significant misalignment). In this regard, it will be recognized that the control schemes for
the applanation motor and the lateral/proximal positioning motor(s) may be coupled to any
degree desired consistent with the invention.
The apparatus 600 is also configured to apply the methodologies of the first, second,
third and fourth processes 102, 104, 106 and 108 previously discussed with respect to Figs. 1
- 5. Details of exemplary implementations of these latter methodologies are described
elsewhere herein.
The physical apparatus 600 of PIG. 6 comprises, in the illustrated embodiment, a
substantially self-contained unit having, inter alia, a combined pressure transducer 622 and
applanation device 600, motor controllers 611, RISC digital processor 608 with associated
synchronous DRAM (SDRAM) memory 617 and instruction set (including scaling lookup
tables), display LEDs 619, front panel input device 621, and power supply 624. In this
embodiment, the controllers 611 are used to control the operation of the combined pressure
transducer/applanation device, who the control and scaling algorithms are implemented on a
continuing basis, based on initial operator/user inputs.
For example, in one embodiment, the user input interface comprises a plurality (e.g.,
two) buttons disposed on the face of the apparatus housing (not shown) and coupled to the
LCD display 679. The processor programming and LCD driver are configured to display
interactive prompts via the display 679 to the user upon depression of each of the two
buttons.
Furthermore, a patient monitor (PM) interface circuit 691 shown in Fig. 6 may be
used to interface the apparatus 600 to an external or third-party patient monitoring system.
Exemplary configurations for such interfaces 691 are described in detail in co-pending U.S.
patent application Ser. No. 10/060,646 entitled "Apparatus and Method for Interfacing Time-
Variant Signals" filed Jan. 30, 2002, and assigned to the Assignee hereof, which is
incorporated by reference herein in its entirely, although other approaches and circuits may
be used. The referenced interface circuit has the distinct advantage of automatically
interfacing with literally any type of patient monitor system regardless of its configuration.
In this fashion, the apparatus 600 of the present invention coupled to the aforementioned
interface circuit allows clinicians end other health care professionals to plug the apparatus
into in situ monitoring equipment already on hand at their facility, thereby obviating the
need (and cost) associated with a dedicated monitoring system just for blood pressure
measurement.
Additionally, an EEPROM 552 is physically coupled to the pressure transducer 622
as shown in FIG. 6 so as to form a unitary unit which is removable from the host apparatus

600. The details of the construction and operation of exemplary embodiments of such
coupled assemblies are described in detail in co-owned U.S. Pat. No. 6,676,600, entitled
"Smart Physiologic Parameter Sensor and Method", issued Jan. 13, 2004, assigned to the
Assignee hereof, and incorporated by reference herein in its entirety, although other
configurations clearly may be substituted. By using such a coupled and removable
arrangement, both the transducer 622 and EEPROM 652 may be readily removed and
replaced within the system 600 by the operator.
It is also noted that the apparatus 600 described herein may be constructed in a
variety of different configurations, and using a variety of different components other than
those specifically described herein. For example, it will be recognized that while many of the
foregoing components such as the processor 608, ADC 609, controller 611, and memory are
described effectively as discrete integrated circuit components, these components and their
functionality may be combined into one or more devices of higher integration level (e.g., so-
called "system-on-chip" (SoC) devices). The construction and operation of such different
apparatus configurations (given the disclosure provided herein) are readily within the
possession of those of ordinary skill in the medical instrumentation and electronics field, and
accordingly not described further nerein.
The computer program(s) for implementing the aforementioned first, second, third
and fourth processes are also included in the apparatus 600. In one exemplary embodiment,
the computer program comprises an object ("machine") code representation of a C++ source
code listing implementing the methodology of FIGS. 1 -5, either individually or in
combination thereof. While C++ language is used for the present embodiment, it will be
appreciated that other programming languages may be used, including for example
VisualBasic™, FORTRAN, and C+. The object code representation of the source code listing
is compiled and may be disposed on a media storage device of the type well known in the
computer arts. Such media storage devices can include, without limitation, optical discs, CD
ROMs, magnetic floppy disks or "hard" drives, tape drives, or even magnetic bubble
memory. These programs may also be embedded within the program memory of an
embedded device if desired. The computer program may further comprise a graphical user
interface (GUI) of the type well known in the programming arts, which is operatively
coupled to the display and input device of the host computer or apparatus on which the
program is run.
In terms of general structure, the program is comprised of a series of subroutines or
algorithms for implementing the applanation and scaling methodologies described herein
based on measured parametric data provided to the host apparatus 600. Specifically, the

computer program comprises tin assembly language/micro-coded instruction set disposed
within the embedded storage device, i.e. program memory, of the digital processor or
microprocessor associated with the hemodynamic measurement apparatus 600. This latter
embodiment provides the advantage of compactness in that it obviates the need for a stand-
alone PC or similar hardware to implement the program's functionality. Such compactness is
highly desirable in the clinical and home settings, where space (and ease of operation) are at
a premium.
As previously noted, one of the significant advantages of the present invention relates
to its flexibility; i.e., that it is essentially agnostic to the hardware/firmware/software on
which it is used, and can be readily adapted to various different platforms or systems for
measuring hemodynamic or other physiologic parameters. For example, the methods and
apparatus of the present invention are substantially compatible with, inter alia, those
described in: co-pending U.S. patent application Ser. No. 10/393,660 "Method and
Apparatus for Control of Non-fnvasive Parameter Measurements" filed Mar. 20, 2003; co-
pending U.S. patent application Ser. No. 10/269,801 entitled "Apparatus and Methods for
Non-lnvasively Measuring Hemodynamic Parameters" filed Oct. 11, 2002;co-pending U.S.
patent application Ser. No. 10/920,990 entitled "Apparatus and Methods for Non-lnvasively
Measuring Hemodynamic Parameters" filed Aug. 18, 2004; co-pending U.S. patent
application Ser. No. TBD entitled "Apparatus and Methods for Non-lnvasively Measuring
Hemodynamic Parameters" filed Jan. 20, 2006; co-pending U.S. Patent No. 6,554,774
entitled "Method and Apparatus for Assessing Hemodynamic Parameters within the
Circulatory System of a Living Subject" issued Apr. 29, 2003, each of the foregoing
assigned to the Assignee hereof and incorporated by reference herein in its entirety.
It is noted that many variations of the methods described above may be utilized
consistent with the present invention. Specifically, certain steps are optional and may be
performed or deleted as desired. Similarly, other steps (such as additional data sampling,
processing, filtration, calibration, or mathematical analysis for example) may be added to the
foregoing embodiments. Additionally, the order of performance of certain steps may be
permuted, or performed in parallel (or series) if desired. Hence, the foregoing embodiments
are merely illustrative of the broader methods of the invention disclosed herein.
While the above detailed description has shown, described, and pointed out novel
features of the invention as applied to various embodiments, it will be understood mat various
omissions, substitutions, and changes in the form and details of the device or process illustrated
may be made by those skilled in the art without departing from the spirit of the invention. The
foregoing description is of the best mode presently contemplated of carrying out the invention.

This description is in no way meant to be limiting, but rather should be taken as illustrative of
the general principles of the invention. The scope of the invention should be determined with
reference to the claims.

WHAT IS CLAIMED IS:
1. Transient-resistant apparatus for determining the blood pressure of a living
subject comprising a processor and a computer program running on said processor, said
program comprising at least one simulated annealing related algorithm.
2. A method of determining hemodynamic parameters using a simulated
annealing-based algorithm.
3. A computer storage medium comprising a computer program adapted for
substantially unified mode operation according to a simulated annealing algorithm,
4. A method of maintaining a substantially optimal level of compression for the
vessel using dynamically applied dither perturbations on at least one axes associated with the
vessel.


Improved apparatus and methods for non-invasively
assessing one or more parameters associated with
systems such as fluidic circulating systems (e.g., the circulatory
system of a living organism). In a first aspect, an improved
method of continuously measuring pressure from a compressible
vessel is disclosed, wherein a substantially optimal
level of compression for the vessel is achieved and maintained
using dynamically applied dither perturbations (e.g., modulation)
on the various axes associated with the vessel. In a second aspect, a
an improved apparatus and method are provided for monitoring hemodyna-
mic parameters, such as blood pressure, in a continuous and non-invas-
ive manner while operating under a single unifying scheme.
One variant of this scheme using a simulated annealing (SA) type
approach to determining and maintaining an optimal operating
state.

Documents:

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Patent Number 270537
Indian Patent Application Number 5076/KOLNP/2008
PG Journal Number 01/2016
Publication Date 01-Jan-2016
Grant Date 29-Dec-2015
Date of Filing 12-Dec-2008
Name of Patentee TENSYS MEDICAL, INC.
Applicant Address 5825 OBERLIN DRIVE, SUITE 100, SAN DIEGO, CA
Inventors:
# Inventor's Name Inventor's Address
1 KATAYAMA, ANDREW S. 1326 GREENLAKE DRIVE, CARDIFF-BY-THE-SEA, CA 92007
2 GOHARLAEE, MANOUCHEHR 1787 SWALLOWTAIL ROAD, ENCINITAS, CA 92024
3 GALLANT, STUART L. 11482 ASH CREEK PLACE, SAN DIEGO, CA 92131
4 CRAYCROFT, WARREN B. 4214 CALLE MEJILLONES, SAN DIEGO, CA 92130
5 KEITEL, TODD A. 5048 ASHBERRY ROAD, CARLSBAD, CA 92008
PCT International Classification Number A61M 25/08
PCT International Application Number PCT/US2007/011598
PCT International Filing date 2007-05-14
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/800,164 2006-05-13 U.S.A.