Title of Invention

AN APPARATUS FOR TISSUE WELDING.

Abstract A system and method for welding of biological tissue by applying an RF voltage during a first stage to electrodes of a tissue welding tool; monitoring tissue impedance, and determining a minimum tissue impedance value during the first stage; determining relative tissue impedance; detecting when the relative tissue impedance reaches a predetermined relative tissue impedance value and starting a second stage; calculating the duration of the second stage as a function of the duration of the first stage; and applying the RF voltage during the second stage to the electrodes of the tissue welding tool (FIG.)1
Full Text [0002] This application is related to U.S. Patent Application NO 09/022,869, entitled
"Bonding of Soft Biological Tissues by Passing High Frequency Electric Current
Therethrough", filed February 12,1998, the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0003] The present invention is related to bonding or welding of soft tissue and, more
apparatus
particularly, to a system apprtus and method for controlling tissue welding.
"requency (RF) electrosurgical tools are widely used in a variety of medical applications for
cutting, soft tissues, hemostasis and various cauterization procedures. Currently-available
electrosurgical bipolar instruments generally use two electrodes of opposite polarity, one of
which is located on each of the opposite jaws of, for example, a grasper. In use, tissue is
held between the electrodes and alternating RF current flows between the two electrodes,
heating the tissue. When the tissue temperature reaches about 30-55 °C, denaturation of
albumens occurs in the tissue. The denaturation of the albumens results in the "unwinding"
of globular molecules of albumen and Iheir subsequent entangling which results in
coagulation of the tissues. Once the tissue is treated in this way, the tissue can be cut in the
welded area with no bleeding. This process is commonly referred to as bipolar coagulation.
[0005] Tissue welding generally comprises bringing together edges of an incision to be
bonded, compressing the tissue with a bipolar tool and heating the tissue by the RF electric
current flowing through them. One of the major differences between tissue welding
procedures and coagulation with the purpose of hemostasis is that tissue welding requires
conditions which allow for the formation of a common albumen space between the tissue to
be bonded before the beginning of albumen coagulation. If such conditions are not present,
coagulation will take place without a reliable connection being"formed.
[0006] Problems which can occur during the tissue welding process include thermal damage
to adjacent structures, over-heating of tissue and under-coagulation. Over-heating of tissue
results in delayed healing, excessive scarring, tissue charring/destruction, and in tissue
sticking to the electrosurgical tool. If tissue sticks to the electrosurgical tool upon removal,
the tissue can be pulled apart at the weld site, adversely affecting hemostasis and causing
further injury. Under-coagulation can occur if insufficient energy has been applied to the
tissue. Under-coagulation results in weak and unreliable tissue welds, and incomplete
hemostasis.
[0007] Precise control of the welding process while avoiding excessive thermal damage,
over-heatine or under-coagulation is a difficult process. particularly when attemDtine to
weld tissue of varying structure, thickness and impedance. The problem of crating a viable
automatic control system is particularly important for welding whose purpose is recovery of
physiological functions of the organs operated on. After hemostasis, vessels or vascularized
tissue parts which have been heated typically do not recover and lose functionality.
[0008] Prior attempts to automate the control of tissue coagulation have met with limited
success. Attempts to avoid over-heating include the use of electrosurgical tools with built-
in temperature measuring devices. Built-in temperature measuring devices are used to
measure the tissue temperature, provide feedback and thereby, prevent overheating.
However, use of built-in temperature sensors causes the electrosurgical tools to be
cumbersome, while providing only limited or inaccurate information about the status of the
inner layers of the tissue between the electrodes where a connection is potentially being
formed.
[0009] Several prior art references suggest various methods of using the tissue impedance
and a minimum tissue impedance value to define a point when coagulation is completed and
tissue heating should be discontinued. Other references suggest use of a relationship
between tissue impedance and current frequency to detect a point of coagulation.
[0010] The prior art methods, however, do not provide effective tissue bonding solutions for
use in surgical procedures and specifically lack the ability to adapt to varying tissue types
and thickness during the welding procedure.
[0011] It would therefore be desirable to provide an electrosurgical system and method
suitable both for tissue bonding and for hemostasis which allows for adaptation to varying
tissue types, structure, thickness, and impedance without over-heating, while providing a
reliable tissue connection. Such a system and method would significantly reduce the time
needed for surgical procedures involving tissue welding by eliminating the need for
equipment adjustment during the welding process.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE ACCOMPANYING DRAWINGS
[0012] The foregoing summary, as well as the following detailed description of preferred
embodiments of the invention, will be better understood when read in conjunction with the
appended drawings. For the purpose of illustrating the invention, there is shown in the
drawings embodiments which are presently preferred. It should be understood, however,
that the invention is not limited to the precise arrangements and instrumentalities shown. In
the drawings:
[0013] Fig. 1 is a block diagram illustrating one embodiment of the invention;
[0014] Fig. 2 shows a plot of the voltage applied during the first stage as a function of time
for one embodiment of the invention;
[0015] Fig. 3 shows a plot of the voltage, tissue impedance and relative tissue impedance
during the first and second stages as a function of time for another embodiment of the
invention;
[0016] Fig. 4 shows a plot of the voltage and tissue impedance during the first and second
stages as a function of time for another embodiment of the invention;
(0017] Fig. 5 shows a plot of the voltage, tissue impedance and relative tissue impedance
during the first and second stages as a function of time for another embodiment of the
invention; and
(0018] Fig. 6 shows a plot of the voltage, tissue impedance and relative tissue Impedance
during the first and second stages as a function of time for another embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention may be applied in a variety of medical procedures involving
the joining or bonding of tissue, to produce both strong tissue welds and minimize thermal
damage to surrounding tissue, that would otherwise result in delayed wound healing. The
system and method of the present invention also provide for automatic adaptation and
control of tissue welding and coagulation processes for tissue of varying structure, thickness
and/or impedance, without the need for equipment adjustment during the welding and
coagulation processes.
[0020] Fig. 1 illustrates one embodiment of the apparatus 10 of the invention including a
power source 100 coupled to electrodes 310 of surgical instrument 300. The power source
is preferably adapted to provide RF voltage to the electrodes 310. The power source 100
preferably also comprises one or more sensors for sensing the RF voltage and current
between the electrodes 310. As shown inFig. I, die sensors preferably include a current
sensor 130 and a voltage sensor 150. The apparatus 10 further comprises a control device
200. The control device 200 preferably includes a microprocessor 210 for controlling the
power source 100 to provide an RF voltage to the electrodes 310 of the surgical instrument
300. Although the conirol device 200 is shown with a microprocessor, the control device
200 could include anyother type of programmable device implemented as a
microcontroller, digital signal processor, or as a collection of discrete logic devices .The
""apparatus 10 may also include an actuation device (not shown) coupled to the control device
200 for actuating control device 200 and power source 100. The apparatus 10 may also
include a control panel or display (not shown) as a user interface.
[0021] The control device 200 is preferably adapted to: control the power source 100 to
provide the RF voltage to the electrodes 310 during a first stage; monitor the tissue
impedance of tissue between the electrodes 310; determine a minimum tissue impedance
value; determine a relative tissue impedance as a ratio of the measured tissue impedance and
the minimum tissue impedance value; detect when the relative tissue impedance reaches a
predetermined relative tissue impedance value during the first stage (the predetermined
relative tissue impedance value being preset or calculated as a function of the RF voltage
variation during the first stage); and control the power source to provide an RF voltage
during a second stage.
[0022] The control device 200 preferably controls the power source 100 to provide the RF
voltage during the first stage such that the RF voltage increases at a gradually decreasing
rate (e.g. a decreasing rate of increase of the RF voltage over time). In one preferred
embodiment, the RF voltage increases according to the following equation:
U = us*tk
where U is voltage, us is a constant, t is time, and k is a constant, and where
k first stage. Varying the RF voltage as described above allows for automatic adjustment of
the welding process when tissue of varying thickness and/or physical properties is
encountered.
[0023] The control device 200 can also be designed to control the power source 100 to
provide an approximation of the gradually increasing RF voltage provided during the first
stage. The approximation is shown in Fig, 2 as a dashed line comprising a plurality of linear
segments.
[0024] The control device 200 preferably calculates tissue impedance Z as a function of
time by dividing the RF voltage by the electric current, determines and stores a minimum
tissue impedance value Zmin, and then calculates a relative tissue impedance z as a function
of time by dividing tissue impedance Z by the minimum tissue impedance value Zmin. The
control device 200 preferably uses a predetermined relative tissue impedance value or
calculates a relative tissue impedance value, at which point the first stage is terminated
(shown in Figs. 3, 5, and 6 as value A). The relative tissue impedance value at which the
first stage is terminated, hereinafter referred to as the "predetermined" relative tissue
impedance value, when calculated, is preferably calculated as a function of the RF voltage
during the first stage (e.g. the greater the RF voltage, the lower the calculated,
predetermined relative tissue impedance value). The predetermined relative tissue
impedance value is preferably within the range of about 1-1.5. When the control device 200
controls the power source 100 to provide an approximation of the RF voltage during the first
stage, the predetermined relative tissue impedance value is preferably calculated or set for
each segment.
[0025] The control device 200 preferably also calculates the RF voltage provided during the
second stage as a function of the value of the RF voltage provided during the first stage
when the relative tissue impedance reaches the predetermined relative tissue impedance
value. The amplitude of the RF voltage provided during the second stage is preferably
between about 50 - 100% of the value of the RF voltage provided at the end of the first
stage (i.e. when the relative tissue impedance reaches the predetermined relative tissue
impedance value).
[0026] In one preferred embodiment, illustrated in Fig. 3, the control device 200 preferably
controls the power source 100 to substantially stabilize the RF voltage provided during the
second stage. The duration of the second stage is preferably calculated by the control
device 200 as a function of the duration of the first stage.
[0027] The control device 200 preferably also controls the power source 100 to modulate
the RF voltages provided during the first and second stages by pulses. The pulses are
preferably square pulses and have a frequency of between about 100 Hz-60 kHz and a duty
cycle of between about 10-90%. A high frequency is preferably selected to prevent cell
membranes from recovering during the interval between pulses.1 The frequency of the
pulses may also be varied during the first and second stages.
[0028] In an alternative embodiment, illustrated in Fig. 4, the control device 200 is designed
to control the power source 100 to modulate the RF voltages applied during the first and
second stages as described above with pulses having a frequency of between about lOOHz-
60 kHz, and further modulate the RF voltage applied during the second stage with low
frequency pulses with a frequency of less than about 100 Hz. The low frequency pulses are
preferably square pulses. More preferably, the control device 200 controls the power source
100 to substantially stabilize the amplitude of the RF voltage applied during the second
stage. The control device 200 preferably calculates the duration of the second stage as a
function of the duration of the first stage. :
[0029] The amplitude of the RF voltage applied during the second stage, shown in Fig. 4 as
B, is preferably calculated as a function of the value of the RF voltage applied at the end of
the first stage (shown in Fig. 4 as C).
[0030] The frequency of the low frequency pulses further modulating the RF voltage during
the second stage is preferably defined as a function of the duration of the first stage. More
preferably, the frequency of the low frequency pulses is defined such that there are between
about 5-10 pulses during the second stage.
[0031] In another alternative embodiment, illustrated in Fig. 5, the control device 200
controls the power source to vary the RF voltage provided during the second stage as a
function of the relative tissue impedance z. Preferably, the control device 200 controls the
power source 100 to provide the RF voltage during the second stage to substantially
stabilize the relative tissue impedance z at a relative tissue impedance level reached at the
end of the first stage (shown in Fig. 5 as A). More specifically, the control device 200 is
preferably designed to control the power source 100 to vary the RF voltage provided during
the second stage as a function of the relative tissue impedance z by reducing the RF voltage
when the relative tissue impedance z is greater than the predetermined relative tissue
impedance value and increasing the RF voltage when the relative tissue impedance z is less
than the predetermined relative tissue impedance value. Alternatively, the control device
200 can control the power source 100 to provide RF voltage during the second stage to vary
the relative tissue impedance according to a preset program. The control device 200
preferably also calculates the duration of the second stage as a function of the duration of
the first stage.
[0032] In another alternative embodiment illustrated in Fig. 6, the control device 200 is
designed to control the power source 100 to modulate the RF voltage provided during the
first and second stages with pulses having a frequency of between about 100 Hz-60 kHz,
and further modulate the RF voltage provided during the second stage with low frequency
pulses. The control device 200 controls the power source 100 to provide the RF voltage
during the second stage to substantially stabilize the relative tissue impedance z at a relative
tissue impedance level reached at the end of the first stage (shown in Fig. 6 as A).
Alternatively,, the control device 200 can control the power source 100 to provide RF
voltage during the second stage to vary the relative tissue impedance according to a preset
program. The control device 200 preferably also calculates the duration of the second stage
as a function of the duration of the first stage.
[0033] In each of the above embodiments the control device 200 preferably can be set to
regulate the modulation pulse frequency to within about 100 Hz - 60 kHz to provide a
minimum tissue resistance. Preferably, regulatory methods known in the art of extremal
systems are used. The control device 200 also preferably regulates the duty cycle of the
modulation pulses during tissue welding such that energy consumption for tissue breakdown
and heating is reduced or minimized. Preferably, regulatory methods known in the art of
extremal self-adjusting systems are used.
[0034] The control device 200 is also preferably capable of controlling the power source
100 to provide modulated pulse bursts of the RF voltage to the electrodes during the
intervals between welding sessions. The duration of a pulse burst is preferably within about
2-15 msec. The frequency of the pulse bursts is preferably within about 3 - 15 Hz. Tissue
welding is preferably actuated if the average tissue resistance of tissue between the
electrodes is less than a preset value.
[0035] The control device 200 is also preferably capable of calculating during welding a
temperature of the electrodes, a temperature of the tissue engaged between the electrodes,
and a degree of tissue coagulation, for example, using a mathematical model and based on
known values of the electric current and RF voltage. The calculated values are preferably
used to adjust the RF voltage increase rate during the first stage and the duration of tissue
welding. Adjustment of the RF voltage increase rate and the duration of tissue welding is
preferably performed using algorithms known in the art of control systems. Preferably,
known tissue coagulation models are used as a model. Adjustment is preferably carried out
within about +/- 15% of the set voltage increase rate and welding duration.
[0036] The frequency of the low frequency pulses, when modulating the RF voltage
provided during the second stage, is preferably defined as a function of the duration of the
first stage. More preferably, the frequency of the low frequency pulses is defined such that
there are between about 5-10 pulses during the second stage.
[0037] Preferably, the control device 200 further comprises a regulatory system (not shown)
for stabilizing or varying the relative tissue impedance z according to a preset program.
Specifically, the regulatory system stabilizes or varies the relative tissue impedance z by
varying the RF voltage by a predetermined amount, the RF voltage being varied based on
the direction of change of the relative tissue impedance z.
[0038] The control device 200 preferably further comprises apparatus for monitoring tissue
welding, and stopping tissue welding and providing a signal to a user if the RF voltage
applied during the first stage reaches a preset RF voltage level and/or if the relative tissue
impedance fails to reach the predetermined relative tissue impedance value.
[0039] The control device 200 preferably further comprises apparatus for monitoring tissue
welding, and stopping tissue welding and providing a signal to a user when the tissue
impedance reaches a short circuit impedance of the electrodes of the tissue welding tool.
[0040] The control device 200 preferably further comprises apparatus for monitoring tissue
welding and providing a signal to a user when tissue welding is completed at the end of the
second stage. The signal is preferably provided after a time lag needed for the welded tissue
to cool off.
[0041] The control device 200 also preferably turns off the RF voltage and provides a
corresponding signal to the user when the tissue impedance or the duration of welding
exceeds threshold parameters.
[0042] The control device 200 preferably further comprises a filter for filtering the tissue
impedance values. The control device 200 can also be designed to control the duration of
the first stage as a function of the relative tissue impedance.
[0043] In one embodiment of the method for welding of biological tissue of the present
invention, the method comprises: applying an RF voltage during a first stage to electrodes of
a tissue welding tool; monitoring tissue impedance, and determining a minimum tissue
impedance value during the first stage; determining relative tissue impedance; detecting
when the relative tissue impedance reaches a predetermined relative tissue impedance value;
starting a second stage when the relative tissue impedance reaches the predetermined
relative tissue impedance value; calculating the duration of the second stage as a function of
the duration of the first stage; and applying the RF voltage during the second stage to the
electrodes of the tissue welding tool.
(0044] The relative tissue impedance is preferably calculated as Hie ratio of tissue
impedance to the minimum tissue impedance value. The RF voltage applied during the first
stage preferably increases at a gradually decreasing rate, preferably according to the
following equation:
U = us*tk
where U is voltage, Us is a constant, t is time, and k is a constant, and where
k [0045] Monitoring tissue impedance preferably includes measuring the RF voltage and
electric current between the electrodes of the tissue welding tool and calculating tissue
impedance by dividing the voltage by the electric current.
[0046] The predetermined relative tissue impedance value is preferably a predetermined or
preset value or is determined as a function of the RF voltage applied during the first stage.
The predetermined relative tissue impedance value is preferably within the range of about 1-
1.5.
[0047] The RF voltage applied during the second stage is preferably calculated as a function
of the value of the RF voltage applied at the end of the first stage (i.e. when the relative
tissue impedance reaches the predetermined relative tissue impedance value). The RF
voltage applied during the second stage is preferably between about 50 - 100% of the value
of the RF voltage applied at the end of the first stage.
[0048] In one preferred embodiment of the method of the present invention, applying the
RF voltage during the second stage comprises substantially stabilizing the RF voltage
applied. Fig. 3 illustrates the method by showing a plot of the RF voltage applied during the
first and second stages, the tissue impedance Z and the relative tissue impedance z. As
shown in Fig. 3, the RF voltage applied during the first stage is gradually increased until the
relative tissue impedance z reaches a predetermined relative tissue impedance value, shown
in Fig. 3 at A. As discussed above, the predetermined relative tissue impedance value can
be preset or determined as a function of the RF voltage applied during the first stage. When
the relative tissue impedance reaches the predetermined relative tissue impedance value, a
substantially stabilized RF voltage is applied during the second stage. The RF voltages
applied during the first and second stages are preferably modulated bv pulses. The pulses
preferably substantially square and have a frequency of between about 100 Hz-60 kHz and a
duty cycle of between about 10-90%. The frequency of the pulses can be varied during the
first and second stages.
[0049] In an alternative embodiment of the method of the present invention, the RF voltages
applied during the first and second stages are modulated with pulses having a frequency of
between about 100 Hz-60 kHz, and the RF voltage applied during the second stage is further
modulated with low frequency pulses. Fig. 4 illustrates the method, showing a plot of the
RF voltage applied during the second stage modulated by low frequency pulses. Preferably,
the amplitude of the RF voltage applied during the second stage is substantially stabilized at
a level shown in Fig. 4 as B. The amplitude of the RF voltage is preferably calculated as a
function of the value of the RF voltage applied at the end of the first stage (shown in Fig 4
as C).
[0050] The low frequency pulses are preferably substantially square pulses. The frequency
of the low frequency pulses modulating the RF voltage applied during the second stage is
preferably defined as a function of the duration of the first stage. More preferably, the
frequency of the low frequency pulses is defined such that there are between about 5-10
pulses during the second stage.
[0051] In another alternative embodiment of the method of the present invention, the RF
voltage applied during the second stage is varied as a function of the relative tissue
impedance. Fig. 5 illustrates the method, showing a plot of the RF voltage and relative
tissue impedance applied during the second stage.
[0052] Preferably the RF voltage applied during the second stage is varied as a function of
the relative tissue impedance by reducing the RF voltage whenthe relative tissue impedance
is greater than the predetermined relative tissue impedance value and increasing the RF
voltage when the relative tissue impedance z is less than the predetermined relative tissue
impedance value. More preferably, the relative tissue impedance is substantially stabilized
at a relative tissue impedance level reached at the end of the first stage. Alternatively, the
RF voltage applied during the second stage can be varied so as to vary the relative tissue
impedance according to a preset program.
[0053] In another alternative embodiment of the method of the present invention, illustrated
in Fig. 6, the RF voltages applied during the first and second stages are modulated with
pulses having a frequency of between about 100 Hz-60 kHz, the RF voltage applied during
the second stage are further modulated with low frequency pulses, and the relative tissue
impedance is substantially stabilized at a relative tissue impedance level reached at the end
of the first stage. Alternatively, the RF voltage applied duringthe second stage can be varied
so as to vary the relative tissue impedance according to a preset program.
[0054] The low frequency pules are preferably square pules. The frequency of the low
frequency pulses is preferably defined as a function of the duration of the first stage. More
preferably, the frequency of the low frequency pulses is defined such that there are between
about 5-10 pulses during the second stage. Stabilizing the relative tissue impedance is
preferably performed by a regulatory system by varying the RF voltage by a predetermined
amount or one step, the sign of the RF voltage change being opposite to the sign of the
relative tissue impedance change.
[0055] The method of each of the above embodiments preferably further comprises
monitoring tissue welding, and stopping tissue welding and providing a signal to a user if
the RF voltage applied during the first stage reaches a preset RF voltage level and/or if the
relative tissue impedance fails to reach the predetermined relative tissue impedance value.
[0056] Preferably the methods of the above embodiments further comprise monitoring
tissue welding and stopping tissue welding and providing a signal to a user when the tissue
impedance reaches a short circuit impedance of the electrodes of the tissue welding tool.
[0057] Preferably the methods of the above embodiments further comprise monitoring
tissue welding and providing a signal to a user when tissue welding is completed at the end
of the second stage. The signal is preferably provided after a time lag needed for the welded
tissue to substantially cool off.
[0058] Preferably the methods of the above embodiments further comprise monitoring
tissue welding and stopping tissue welding and providing a signal to a user when the tissue
impedance or the duration of welding exceeds threshold parameters.
[0059] In another embodiment of the present invention, a control method is provided for
welding of biological tissue comprising: applying an increasing RF voltage, preferably
increasing at a gradually decreasing rate, to the electrodes of a tissue welding tool during a
first stage; measuring the values of the RF voltage and electric current passing through the
tissue, and the duration of the first stage; calculating tissue impedance values by dividing
the RF voltage values by the electric current values; determining a minimum tissue
impedance value; storing the minimum tissue impedance value; calculating relative tissue
impedance values by dividing the values of the tissue impedance by the minimum tissue
impedance value; stopping the first stage when the relative tissue impedance reaches an
endpoint relative tissue impedance value calculated as a function of the relative tissue
impedance; storing the duration of the first stage and a value of the RF voltage at the end of
the first stage (i.e. when the relative tissue impedance reaches She endpoint relative tissue
impedance value); calculating an RF voltage level for a second stage as a function of the
value of the RF voltage at the end of the first stage; calculating the duration of the second
stage as a function of the duration of the first stage; and applying an RF voltage during the
second stage at the RF voltage level calculated above.
(0060] In another embodiment of the present invention, a control method is provided for
welding of biological tissue comprising: applying an increasing RF voltage, preferably
increasing at a gradually decreasing rate, to the electrodes of a tissue welding tool during a
first stage; measuring the values of the RF voltage and electric current passing through the
tissue, and the duration of the first stage; calculating tissue impedance values by dividing
the RF voltage values by the electric current values; determining a minimum tissue
impedance value; storing the minimum tissue impedance value; calculating a relative tissue
impedance value by dividing the tissue impedance values by the minimum tissue impedance
value; stopping the first stage when the relative tissue impedance reaches an endpoint
relative tissue impedance value calculated as a function of the relative tissue impedance;
storing the duration of the first stage and the RF voltage at the end of the first stage;
calculating an RF voltage level for a second stage as a function of the value of the RF
voltage at the end of the first stage; calculating the duration of the second stage as a function
of the duration of the first stage; calculating a modulation frequency as a function of the
duration of the first stage; and applying an RF voltage at the RF voltage level calculated
above for the duration of the second stage calculated above, and modulating the RF voltage
by pulses at the modulation frequency calculated above.
[0061] In another embodiment of the present invention, a control method is provided for
welding of biological tissue comprising: applying an increasing RF voltage, preferably
increasing at a gradually decreasing rate, to the electrodes of a tissue welding tool during a
first stage; measuring the values of the RF voltage and electric current passing through the
tissue, and the duration of the first stage; calculating tissue impedance values by dividing
the RF voltage values by the electric current values; determining a minimum tissue
impedance value; storing the minimum tissue impedance value; calculating a relative tissue
impedance value by dividing the tissue impedance values by the minimum tissue impedance
value; stopping the first stage when the relative tissue impedance reaches an endpoint
relative tissue impedance value calculated as a function of the relative tissue impedance;
storing the duration of the first stage and a value of the RF voltage at the end of the first
stage; calculating the duration of the second stage as a function of the duration of the first
stage; and applying the RF voltage during the second stage, wherein the RF voltage is
varied as a function of the relative tissue impedance during the second stage.
[0062] In another embodiment of the present invention, a control method is provided for
welding of biological tissue comprising: applying an increasing RF voltage, preferably
increasing at a gradually decreasing rate, to the electrodes of a tissue welding tool during a
first stage; measuring the values of the RF voltage and electric current passing through the
tissue; calculating tissue impedance values by dividing the RF voltage values by the electric
current values; determining a minimum tissue impedance value; storing the minimum tissue
impedance value; calculating relative tissue impedance values by dividing the tissue
impedance values by the minimum tissue impedance values; stopping the first stage when
the relative tissue impedance reaches an endpoint relative tissue impedance value calculated
as a function of the relative tissue impedance; storing the duration of the first stage and a
value of the RF voltage; calculating an initial RF voltage level for a second stage as a
function of the value of the RF voltage at the end of the first stage; calculating the duration
of the second stage as a function of the duration of the first stage; calculating a modulation
frequency as a function of the duration of the first stage; and applying an RF voltage for the
duration of the second stage calculated above, initially setting the amplitude of the RF
voltage to the initial RF voltage level calculated above, modulating the RF voltage by pulses
at the modulation frequency calculated above, and varying the amplitude of the RF voltage
as a function of the relative tissue impedance.
[0063] Preferably the method further comprises stabilizing the; relative tissue impedance
during the second stage at the endpoint relative tissue impedance value. Stabilizing the
relative tissue impedance is preferably performed by a regulatory system which stabilizes
the relative tissue impedance by varying the RF voltage pulses by a predetermined amount,
the RF voltage being varied based on the change of the relative tissue impedance.
Preferably, the regulatory system stabilizes the relative tissue impedance by varying the RF
voltage pulses by a predetermined amount starting with a calculated initial level.
[0064] Preferably the method further comprises varying the relative tissue impedance
according to a preset method, this variation preferably being made by the regulatory system
affecting the amplitude of the RF voltage pulses.
[0065] The present invention may be implemented with any combination of hardware and
software. If implemented as a computer-implemented apparatus, the present invention is
implemented using means for performing all of the steps and functions described above.
The present invention can also be included in an article of manufacture (e.g., one or more
computer program products) having, for instance, computer useable media. The media has
embodied therein, for instance, computer readable program code means for providing and
facilitating the mechanisms of the present invention. The article of manufacture can be
included as part of a computer system or sold separately.
[0066] It will be appreciated by those skilled in the art that changes could be made to the
embodiments described above without departing from the broad inventive concept thereof.
It is understood, therefore, that this invention is not limited to the particular embodiments
disclosed, but it is intended to cover modifications within the spirit and scope of the present
invention as defined by the appended claims.
1. An apparatus for tissue welding comprising:
a surgical instrument having electrodes adapted to engage tissue to be welded;
a power source coupled to the electrodes for providing radio frequency voltage,
the power source including one or more sensors for sensing the radio frequency voltage
and current between the electrodes; and
a control device coupled to the power source;
wherein the control device: controls the power source to provide a radio
frequency voltage to the electrodes during a first stage; monitors tissue impedance;
determines a minimum tissue impedance value; determines relative tissue impedance as a
ratio of the measured tissue impedance and the minimum tissue impedance value; detects
when the relative tissue impedance reaches a predetermined relative tissue impedance
value; and controls the power source to provide a radio frequency voltage during a
second stage, the duration of the second stage being calculated by the control device as a
function of the duration of the first stage.
2. The apparatus as claimed in claim 1 wherein the control device controls the
power source to provide the radio frequency voltage during the first stage such that the
radio frequency voltage increases according to the following equation:
U = us *tk
where U is voltage, us is a constant, t is time, and k is a constant and where k 3. The apparatus as claimed in claim 1 wherein the control device calculates tissue
impedance as a function of time by dividing the radio frequency voltage by the electric
current.
4. The apparatus as claimed in claim 1 wherein the predetermined relative tissue
impedance value is calculated as a function of the radio frequency voltage variation
during the first stage.
5. The apparatus as claimed in claim 1 wherein the predetermined relative tissue
impedance value is within the range of 1-1.5.
6. The apparatus as claimed in claim 1 wherein control device calculates the radio
frequency voltage provided during the second stage as a function of the value of the radio
frequency voltage provided during the first stage when the relative tissue impedance
reaches the predetermined relative tissue impedance value.
7. The apparatus as claimed in claim 1 wherein the radio frequency voltage provided
during the second stage is between 50-100% of the value of the radio frequency voltage
provided during the first stage when the relative tissue impedance reaches the
predetermined relative tissue impedance value.
8. The apparatus as claimed in claim 1 wherein the control device controls the
power source to substantially stabilize the radio frequency voltage provided during the
second stage.
9. The apparatus as claimed in claim 1 wherein the control device controls the
power source to modulate the radio frequency voltages provided during the first and
second stages by pulses.
10. The apparatus as claimed in claim 9 wherein the pulses have a frequency of
between 100Hz-60kHz and a duty cycle of between 10-90%.
11. The apparatus as claimed in claim 9 wherein the frequency of the pulses is varied
during the first and second stages.
12. The apparatus as claimed in claim 1 wherein the control device controls the
power source to modulate the radio frequency voltage applied during the first and second
stages with pulses having a frequency of between 100 Hz-60kHz, and modulate the
radio frequency voltage applied during the second stage with low frequency pulses.
13. The apparatus as claimed in claim 12 wherein the control device controls the
power source to substantially stabilizing the radio frequency voltage applied during the,
second stage, wherein the amplitude of the radio frequency voltage is calculated as a
Junction of the value of the radio frequency voltage applied during the first stage when
the relative tissue impedance reaches the predetermined relative tissue impedance value.
14. The apparatus as claimed in claim 12 wherein the frequency of the low frequency
pulses is defined as a function of the duration of the first stage.
15. The apparatus as claimed in claim 12 wherein the frequency of the low frequency
pulses is defined such that there are between 5-10 pulses during the second stage.
16. The apparatus as claimed in claim 1 wherein the control device controls the
power source to vary the radio frequency voltage provided during the second stage as a
function of the relative tissue impedance.
17. The apparatus as claimed in claim 16 wherein the control device controls the
power source to vary the radio frequency voltage during the second stage to substantially
stabilize the relative tissue impedance at a relative tissue impedance level reached at the
end of the first stage.
18. The apparatus as claimed in claim 16 wherein the control device controls the
power source to vary the radio frequency voltage provided during the second stage as a
function of the relative tissue impedance by reducing the radio frequency voltage when
the relative tissue impedance is greater than the predetermined relative tissue impedance
value and increasing the voltage when the relative tissue impedance is less than the
predetermined relative tissue impedance value.
19. The apparatus as claimed in claim 1 wherein the control device controls the
power source to provide the radio frequency voltage during the second stage to regulate
the relative tissue impedance.
20. The apparatus as claimed in claim 1 wherein the control device controls the
power source to modulate the radio frequency voltage provided during the first and
second stages with pulses having a frequency of between 100Hz-60kHz, and modulate
the radio frequency voltage provided during the second stage with low frequency pulses,
and wherein the control device controls the power source to provide an radio frequency
voltage during the second stage which substantially stabilizes the relative tissue
impedance at a relative tissue impedance level reached at the end of the first stage.
21. The apparatus as claimed in claim 20 wherein the frequency of the low frequency
pulses is defined as a function of the duration of the first stage.
22. The apparatus as claimed in claim 20 wherein the frequency of the low frequency
pulses is defined such that there are between about 5-10 pulses during the second stage.
23. The apparatus as claimed in claim 20 wherein the control device comprises a
regulatory system for stabilizing the relative tissue impedance.
24. The apparatus as claimed in claim 23 wherein the regulatory system stabilizes the
relative tissue impedance by varying the radio frequency voltage by a predetermined
amount, the radio frequency voltage being varied based on the direction of change of the
relative tissue impedance.
25. The apparatus as claimed in claim 1 wherein the control device controls the
power source to modulate the radio frequency voltage provided during the first and
second stages with pulses having a frequency of between 100Hz-60kHz, and modulate
the voltage provided during the second stage with low frequency pulses, and wherein the
control device controls the power source to provide an radio frequency voltage during the
second stage to regulate the relative tissue impedance.
26. The apparatus as claimed in claim 1 comprising a regulatory system for regulating
the relative tissue impedance by varying the radio frequency voltage by a predetermined
amount, the radio frequency voltage being varied based on the direction of change of the
relative tissue impedance.
27. The apparatus as claimed in claim 1 wherein the control device comprises
apparatus for monitoring tissue welding, and stopping tissue welding and providing a
signal to a user if the radio frequency voltage applied during the first stage reaches a
preset radio frequency voltage level and/or if the relative tissue impedance fails to reach
the predetermined relative tissue impedance level.
28. The apparatus as claimed in claim 1 wherein the control device comprises
apparatus for monitoring tissue welding and stopping tissue welding and providing a
signal to a user when the tissue impedance reaches a short circuit impedance of the
electrodes of the tissue welding tool.
29. The apparatus as claimed in claim 1 wherein the control device comprises
apparatus for monitoring tissue welding and providing a signal to a user after tissue
welding is completed at the end of the second stage and the welded tissue has sufficiently
cooled.
30. The apparatus as claimed in claim 1 wherein the control device comprises
apparatus for monitoring tissue welding, and if the tissue impedance exceeds a preset
value and/or if the duration of the first stage exceeds a preset duration, the control device
maintains the radio frequency voltage at a steady level for a preset period and stops tissue
welding and provides a signal to a user if the relative tissue impedance does not reach the
predetermined relative tissue impedance value.
31. The apparatus as claimed in claim 1 wherein the control device controls the
power source to provide an approximation of a gradually increasing radio frequency
voltage during the first stage by means of a plurality of linear segments.
32. The apparatus as claimed in claim 1 wherein the control device comprises a filter
for filtering the tissue impedance values.
33. The apparatus as claimed in claim 1 wherein the control device controls the
duration of the first stage as a function of the relative tissue impedance.
34. The apparatus as claimed in claim 9 wherein the control device regulates the
modulation pulse frequency within 100Hz-60kHz to provide minimum tissue resistance.
35. The apparatus as claimed in claim 9 wherein the control device regulates the duty
cycle of modulation pulses during tissue welding such that energy consumption for tissue
breakdown and heating is minimized.
36. The apparatus as claimed in claim 1 wherein the control device controls the
power source to provide modulated pulse bursts of the radio frequency voltage to the
electrodes during the intervals between welding sessions, the duration of a pulse burst
being within about 2-15 msec, the frequency of pulse bursts being within 3-15Hz, and
wherein welding is actuated if the average resistance between the electrodes is less than a
preset value.
37. The apparatus as claimed in claim 1 wherein the control device calculates during
welding a temperature of the electrodes, a temperature of the tissue engaged between the
electrode and a degree of tissue coagulation using a mathematical model and based on
known values of the electric current and voltage.
38. The apparatus as claimed in claim 37 wherein the calculated values are used to
adjust the voltage increase rate during the first stage and the duration of tissue welding.
39. An apparatus for welding of biological tissue comprising:
(a) means for applying an radio frequency voltage during a first stage to
electrodes of a tissue welding tool;
(b) means for monitoring tissue impedance, and determining a minimum
tissue impedance value during the first stage;
(c) means for determining relative tissue impedance, the relative tissue
impedance being equal to the ratio of tissue impedance to the minimum
tissue impedance value;
(d) means for detecting when the relative tissue impedance reaches a
predetermined relative tissue impedance value;
(e) means for starting a second stage when the relative tissue impedance
reaches the predetermined relative tissue impedance value;
(f) means for calculating the duration of the second stage as a function of the
duration of the first stage; and
(g) means for applying the radio frequency voltage during the second stage to
the electrodes of the tissue welding tool.
40. The apparatus as claimed in claim 39 wherein the amplitude of the radio
frequency voltage applied during the first stage increases according to the following
equation:
U = u.*tk
where U is voltage, us is constant, t is time and k is a constant, and where k 41. The apparatus as claimed in claim 39 wherein the means for monitoring tissue
impedance comprises means for measuring the radio frequency voltage and electric
current between the electrodes of the tissue welding tool and calculating tissue
impedance by dividing the voltage by the electric current.
42. The apparatus as claimed in claim 39 wherein the predetermined relative tissue
impedance value is calculated as a function of the radio frequency voltage during the first
stage.
43. The apparatus as claimed in claim 39 wherein the predetermined relative tissue
impedance value is within the range of 1-1.5.
44. The apparatus as claimed in claim 39 wherein the radio frequency voltage
applied during the second stage is calculated as a function of the value of the radio
frequency voltage applied during the first stage when the relative tissue impedance
reaches the predetermined relative tissue impedance value.
45. The apparatus as claimed in claim 39 wherein the radio frequency voltage
applied during the second stage is between 50-100% of the value of the radio frequency
voltage applied at the end of the first stage.
46. The apparatus as claimed in claim 39 wherein the means for applying the radio
frequency voltage during the second stage comprises means for substantially stabilizing
the radio frequency voltage applied during the second stage.
47. The apparatus as claimed in claim 39 comprising means for modulating the radio
frequency voltages applied during the first and second stages by pulses.
48. The apparatus as claimed in claim 47 wherein the pulses have a frequency of
between 100Hz-60kHz and a duty cycle of between 10-90%.
49. The apparatus as claimed in claim 47 wherein the frequency of the pulses is
varied during the first and second stages.
50. The apparatus as claimed in claim 39 comprising means for modulating the radio
frequency voltages applied during the first and second stages with pulses having a
frequency of between 100Hz-60kHz, and modulating the radio frequency voltage applied
during the second stage with low frequency pulses.
51. The apparatus as claimed in claim 50 comprising means for substantially
stabilizing the amplitude of the radio frequency voltage applied during the second stage,
wherein the amplitude of the radio frequency voltage is calculated as a function of the
value of the radio frequency voltage at the end of the first stage.
52. The apparatus as claimed in claim 50 wherein the frequency of the low frequency
pulses is defined as a function of the duration of the first stage.
53. The apparatus as claimed in claim 50 wherein the frequency of the low frequency
pulses is defined such that there are between 5-10 pulses during the second stage.
54. The apparatus as claimed in claim 39 wherein the means for applying the radio
frequency voltage during the second stage comprises means for varying the radio
frequency voltage as a function of the relative tissue impedance.
55. The apparatus as claimed in claim 54 comprising means for substantially
stabilizing the relative tissue impedance at a relative tissue impedance level reached at
the end of the first stage.
56. The apparatus as claimed in claim 54 wherein the radio frequency voltage applied
during the second stage is varied as a function of the relative tissue impedance by
reducing the radio frequency voltage when the relative tissue impedance is greater than
the predetermined relative tissue impedance value and increasing the radio frequency
voltage when the relative tissue impedance is less than the predetermined relative tissue
impedance value.
57. The apparatus as claimed in claim 39 wherein the means for applying the radio
frequency voltage during the second stage comprises means for varying, the radio
frequency voltage to vary the relative tissue impedance according to a preset program.
5$. The apparatus as claimed in claim 39 comprising means for modulating the radio
frequency voltages applied during the first and second stages with pulses having a
frequency of between 100Hz-60kHz, and modulating the radio frequency voltage applied
during the second stage with low frequency pulses, and comprising means for
substantially stabilizing the relative tissue impedance at a relative tissue impedance level
reached at the end of the first stage.
59. The apparatus as claimed in claim 58 wherein the frequency of the low frequency
pulses is defined as a function of the duration of the first stage.
60. The apparatus as claimed in claim 58 wherein the frequency of the low frequency
pulses is defined such that there are between 5-20 pulses during the second stage.
61. The apparatus as claimed in claim 58 wherein stabilizing the relative tissue
impedance is performed by a regulatory system means.
62. The apparatus as claimed in claim 61 wherein the regulatory system means
stabilizes the relative tissue impedance by varying the radio frequency voltage by a
predetermined amount, the radio frequency voltage being varied based on the direction of
change of the relative tissue impedance.
63. The apparatus as claimed in claim 39 comprising msans for modulating the radio
frequency voltages applied during the first and second stages with pulses having a
frequency of between 100Hz-60kHz, and modulating the radio frequency voltage applied
during the second stage with low frequency pulses and comprising means for varying
radio frequency voltage to vary the relative tissue impedance according to a preset
program.
64. The apparatus as claimed in claim 63 wherein varying the relative tissue
impedance is performed by a regulatory system means.
65. The apparatus as claimed in claim 39 comprising means for monitoring tissue
welding, and stopping welding and providing a signal to a user if the radio frequency
voltage applied during the first stage reaches a preset radio frequency voltage level and/or
if the relative tissue impedance fails to reach the predetermined relative tissue impedance
value.
66. The apparatus as claimed in claim 39 comprising means for monitoring tissue
welding and stopping tissue welding and providing a signal to a user when the tissue
impedance reaches a short circuit impedance of the electrodes of the tissue welding tool.
67. The apparatus as claimed in claim 39 comprising means for monitoring tissue
welding and providing a signal to a user after tissue welding is completed at the end of
the second stage and the welded tissue has sufficiently cooled.
The present invention discloses an apparatus for tissue welding comprising:
a surgical instrument having electrodes (310) adapted to engage tissue to be welded;
a power source (100) coupled to the electrodes for providing radio frequency voltage, the power source including one or more sensors for sensing the radio frequency voltage and current between the electrodes; and
a control device (200) coupled to the power source;
wherein the control device: controls the power source to provide a radio frequency voltage to the electrodes during a first stage; monitors tissue impedance; determines a minimum tissue impedance value; determines relative tissue impedance as a ratio of the measured tissue impedance and the minimum tissue impedance value; detects when the relative tissue impedance reaches a predetermined relative tissue impedance value; and controls the power source to provide a radio frequency voltage during a second stage, the duration of the second stage being calculated by the control device as a function of the duration of the first stage. Figure 1.

Documents:

1374-kolnp-2004-granted-abstract.pdf

1374-kolnp-2004-granted-assignment.pdf

1374-kolnp-2004-granted-claims.pdf

1374-kolnp-2004-granted-correspondence.pdf

1374-kolnp-2004-granted-description (complete).pdf

1374-kolnp-2004-granted-drawings.pdf

1374-kolnp-2004-granted-form 1.pdf

1374-kolnp-2004-granted-form 18.pdf

1374-kolnp-2004-granted-form 3.pdf

1374-kolnp-2004-granted-form 5.pdf

1374-kolnp-2004-granted-gpa.pdf

1374-kolnp-2004-granted-letter patent.pdf

1374-kolnp-2004-granted-reply to examination report.pdf

1374-kolnp-2004-granted-specification.pdf


Patent Number 212696
Indian Patent Application Number 01374/KOLNP/2004
PG Journal Number 50/2007
Publication Date 14-Dec-2007
Grant Date 12-Dec-2007
Date of Filing 16-Sep-2004
Name of Patentee LIVE TISSUE CONNECT INC.
Applicant Address CORPUS CHRISTI, TEXAS 78471, USA.
Inventors:
# Inventor's Name Inventor's Address
1 PATON BORIS E. 41A CHKALOVA STRAPT 26 NONE KIEV UKRAINE
2 LEBEDEV VLADIMIR K. 7/10, LUTHERABSJAYA STR APT 15, NONE KIE UKRAINE
3 ;EBEDEV ALEXEO V. 7/10, LUTHERNSKAYA STR APT 15 NONE KIEV UKRAINE
4 IVANOVA OLA N. 25 SCHORSA STR APT 6, NONE KIEV UKRAINE.
5 ZAKHARASH MYKHAIL OP 14 BEKHTEREVSKIY STR APT 21, NONE KIEV UKRAINE.
6 FURMANOV YURI, A 42/1 BLD 12P0ROSPEK NAUKY APT 15 NONE KIEV UKRAINE
7 MASALOV YURII A. 1/28, FILATOVA STR APT 30, NONE KIEV UKRAINE
PCT International Classification Number A61L
PCT International Application Number PCT/US03/04679
PCT International Filing date 2003-02-13
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/078, 828 2002-02-19 U.S.A.