U.S. patent number 3,923,063 [Application Number 05/488,281] was granted by the patent office on 1975-12-02 for pulse control circuit for electrosurgical units.
This patent grant is currently assigned to Sybron Corporation. Invention is credited to Stephen William Andrews, Stanley Woltosz.
United States Patent |
3,923,063 |
Andrews , et al. |
December 2, 1975 |
Pulse control circuit for electrosurgical units
Abstract
A control circuit for electrosurgical units establishes a
particular output signal to patient electrodes in response to
condition of the patient electrodes. The duty cycle of the output
signal is reduced when the patient electrodes are not in contact
with the patient so as to prevent unwanted cutting and the duty
cycle is increased when both patient electrodes are in contact with
the patient so as to maximize the coagulation effect.
Inventors: |
Andrews; Stephen William
(Rochester, NY), Woltosz; Stanley (Rochester, NY) |
Assignee: |
Sybron Corporation (Rochester,
NY)
|
Family
ID: |
23939087 |
Appl.
No.: |
05/488,281 |
Filed: |
July 15, 1974 |
Current U.S.
Class: |
606/38 |
Current CPC
Class: |
A61B
18/16 (20130101); A61B 18/1206 (20130101); A61B
2018/00642 (20130101); A61B 2018/00726 (20130101) |
Current International
Class: |
A61B
18/12 (20060101); A61B 18/16 (20060101); A61B
18/14 (20060101); A61N 003/00 () |
Field of
Search: |
;128/303.14,303.13,303.17,303.18,21P |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
855,459 |
|
Nov 1960 |
|
UK |
|
897,961 |
|
Jun 1962 |
|
UK |
|
1,146,989 |
|
Apr 1963 |
|
DT |
|
1,178,528 |
|
Sep 1964 |
|
DT |
|
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Roessel; Theodore B. Yeo; J.
Stephen
Claims
We claim:
1. In combination with an electrosurgical unit having a plurality
of patient electrodes and RF generating means for providing an
output voltage across said electrodes, a pulse control circuit
connected to said electrosurgical unit for pulse modulating said
output signal and controlling the duty cycle of said pulse
modulated output signal applied to said plurality of patient
electrodes, said pulse control circuit comprising:
voltage circuit means for sampling the magnitude voltage between
said patient electrodes;
threshold circuit means for generating a threshold signal when the
magnitude of said voltage between said patient electrodes exceeds a
predetermined level, and
modulator circuit means for pulse modulating said output signal at
a first duty cycle in the absence of said threshold signal and at a
second duty cycle in response to said threshold signal.
2. A pulse control circuit as defined with claim 1 which further
includes:
control circuit means for producing a control signal; and
enabling circuit means interposed between said threshold circuit
means and said modulating circuit means, said enabling circuit
means being in communication with said control circuit means and
responsive to said control signal for connecting said threshold
signal with said modulating circuit means.
3. A pulse control circuit as defined in claim 1 wherein,
said voltage circuit means includes two capacitors connected in
series between said patient electrodes.
4. A pulse control circuit as defined in claim 1 wherein said
modulator circuit means includes:
a transistor, and
sawtooth generating means for supplying a periodic sawtooth signal
to said transistor, said transistor also being coupled with said
threshold circuit means whereby the conductive state of said
transistor is determined by said sawtooth signal and said threshold
signal;
wherein said electrosurgical unit includes RF signal amplifier
means connected to said transistor and controlled as said
transistor so that when said transistor is conductive said RF
signal amplifier means is operative.
5. A pulse control circuit as defined as claim 1 wherein said first
duty cycle is higher than said second duty cycle.
Description
This invention includes method of adjusting coagulation power by
varying the duty cycle and not the amplitude of the output
signal.
BACKGROUND OF THE INVENTION
This invention relates generally to rf modulation circuits and more
particularly concerns rf modulation circuits for use in
electrosurgical units. Electrosurgical units use high frequency
(RF) power for cutting and coagulation of tissue under surgical
conditions. The electrosurgical units apply a high frequency
alternating current at power levels up to several hundred watts to
electrodes usually consisting of an active probe and a dispersive
plate generally known as a patient plate.
Two main types of current are provided, one for cutting and one for
coagulation. The optimal cutting current is a continuous wave
output from the electrosurgical unit. For smooth cutting a
continuous arc is required between the active probe and the
patient. Upon application of a high power continuous wave arc, the
tissue cells volatize resulting in a smooth cutting action as the
probe is moved along the surface of the tissue. To introduce
hemostasis, the cutting current the wave form is pulsed. The lower
the duty cycle, the greater will be the amount of hemostasis and
the less the cutting effect. Duty cycle is defined as the ratio of
pulse on time to duration of the total pulse times 100%. For
effective coagulation a current with a duty cycle of approximately
20% to less than 5% is required. The longer off--time with a low
duty cycle allows the tissue to cool off, so as to avoid
volatization of cells, but enough power must be applied to sear off
exposed blood vessels.
Both electrodes are available in various configurations to be
selected by the surgeon according to the intended use. The active
probe selected by the surgeon can range in size from a pair of
forceps or a knife blade to a fine needle. The contact area of the
probe and the type of tissue encountered are factors determining
the amount of power necessary to effectively cut or coagulate the
blood vessels contigous to the operating situs.
Electrosurgical units have previously used either spark gap or
vacuum tube methods to achieve radio frequency levels of several
hundred watts. For many years the generator used for producing a
coagulation current was a spark gap type of generator. A spark gap
oscillator can generate large peak powers at a low duty cycle while
maintaining about 120 watts of average power. Spark gap methods,
however, generate white noise whereas spectrum purity is desirable
with electrosurgical units, particularly since electronic equipment
is becoming more prevalent in hospitals. Vacuum tube units are
capable of generating a power output of several hundred watts in
the megahertz range, but, they generally also operate at low
efficiency and have low reliability compared to presently available
solid state circuitry. With the advent of solid state units it has
been found that presently available transistors cannot generate the
large amounts of peak power required under some conditions. Hence,
so the duty cycle had to be increased to allow for adequate average
power, but, the larger duty cycle introduced a cutting effect in
the coagulation mode. To minimize the cutting effect in the
coagulation mode, a low duty cycle is required.
The amount of power required varies depending upon whether the
active probe is arcing or in physical contact with the tissue and
is also dependent upon the effective current density at the
operating site, as determined by the contact area of the probe. All
electrosurgical units on the market today employ amplitude control
to vary the amount of coagulation power since a low duty cycle
results in less cutting effect it would, therefore, be desirable to
vary the duty cycle of electrosurgical units in response to load
conditions as opposed to varying the amplitude control.
SUMMARY OF THE INVENTION
A pulse control circuit for an electrosurgical unit control the
duty cycle of a pulse modulated output signal. The output signal is
applied to a plurality of patient electrodes. The voltage across
the electrodes is sampled preferably by a capacitive voltage
divider, and controls a threshold circuit. When the voltage between
the patient electrodes exceeds a predetermined level, the threshold
circuit, preferably a Schmidt Trigger, generates a signal, which is
applied to the modulator circuit of the electrosurgical unit. The
presence of absence of the signal determines the duty cycle of the
unit. The threshold circuit may be selectively connected with the
modulator circuit so as to enable or disable its application
according to use.
The electrosurgical unit may also be manually operated so as to
control the average power by providing a pulse modulated output
signal having a constant amplitude and varying the duty cycle of
the output signal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an electrosurgical unit which includes
the pulse control circuit of the present invention.
FIG. 2 is a schematic representation of the pulse control circuit
of FIG. 1 .
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an electrosurgical unit which includes
the pulse control circuit of the present invention. An oscillator
10 generates a continuous wave RF signal. The RF signals are
applied to the input of an amplifier 12. A modulator circuit 14
which drives amplifier 12 on and off, The result is that the RF
signal is pulse modulated by the amplifier 12 as driven by the
modulator circuit 14. Control means 16 is used by the operator to
select the desired modulation mode suitable for the surgical
functions of cutting, cutting with hemostasis, and coagulation
which are dependent upon the shape of output wave form and the duty
cycle. A power amplifier 18 amplifies the modulated signals from
amplifier 12 to a power level of approximately 400 watts. The
amplifier signals are coupled from the power amplifier 18 by a
transformer 20 to a pair of patient electrodes which include an
active probe 22 and a patient plate 24. The patient 26 maintains
continual contact with the patient plate 24 during the surgical
operation. The active probe 22 is used for surgical procedures.
In accordance with a first feature of the invention, two capacitors
28 and 30 are connected in series between the active probe 22 and
the patient plate 24. The purpose of the capacitors 28 and 30 is to
act as a voltage divider so as to sample the voltage potential
between the active probe 22 and the patient plate 24. It should be
noted that other voltage dividers such as two resistors or other
elements could also be used in this fashion instead of capacitors.
The input terminals of a threshold circuit 32 are connected across
the capacitor 30. It is seen that the voltage across the input of
the threshold circuit 32 is the same voltage that appears across
capacitor 30.
The property of the threshold circuit 32 is to generate an output
signal when the input signal exceeds a preset magnitude. The input
voltage will be of low magnitiude or high magnitude depending upon
whether the active probe 22 is or is not in contact with the
patient 26. When the active probe 22 is not in contact with the
patient 26 the voltage across capacitor 30 will be in the high
state and of sufficient magnitude to cause the threshold circuit 32
to thereby generate an output signal. The output signal from the
threshold circuit 32 is connected to the modulated circuits 14
through an enabling circuit 34. The enabling circuit 34 is enabled
by the control circuit 16. When the control circuit 16 is set by
the operator so as to be in the coagulating mode the enable circuit
34 will be turned on so as to allow the output from the threshold
circuit to reach the modulator circuit 14. In the coagulation mode,
modulator circuit 14 can be adjusted to modulate the signal, for
example, with 20% duty cycle in the absence of a threshold output
signal. As will be described in further detail in a later portion
of the specification the presence of a threshold signal has the
affect of reducing the duty cycle of the RF signal, for example,
from 20% to 5%. This reduction in duty cycle remains in effect
until the active probe 22 becomes in contact with the patient 26 at
which time the voltage across capacitor 30 and input signal to the
threshold circuit 32 drops preventing the generation of the
threshold output signal. The removal of the threshold output signal
allows the modulated RF signal to return to the higher
predetermined duty cycle of 20% in our example. The purpose of
controlling of the duty cycle is to avoid cutting of the patient
tissue while the electrosurgical unit is in the coagulation mode.
It has been found that substantial cutting will occur when the
active probe is not in contact with the patient but when at such a
distance as to substain an arc between the active probe 22 and the
patient 26. During coagulation it is desirable to reduce the duty
cycle under arcing condition by reducing the average power
dissipated at the operating site thereby reducing the cutting
effect. When the active probe has made contact with the patient 26
a high power level is permissible as there is no longer an arc
substained so that unwanted cutting is eliminated. The higher
average power is desirable to obtain the desired coagulation. When
the control circuit 16 is switched to be in the cutting mode, the
enable circuit 34 is disabled so as to prevent the threshold output
signal from the threshold circuit 32 from reaching the modulation
circuit 14, thereby the duty cycle of the RF signal remains
constant regardless of active probe 22 contact with the patient 26.
The duty cycle of the modulator 14 may be changed by the control
circuit 16 to 100% during cutting mode to provide maximum average
power under all cutting conditions. A reduction of this duty cycle
while in the cutting mode will provide hemostasis in the cutting
mode.
FIG. 2 is a schematic representation of the threshold circuit 32,
the enable circuit 34, the modulation circuit 14, the input
amplifier circuit 12 and the control circuit 16 of FIG. 1. The
threshold circuit 32 includes a conventional Schmidt trigger
circuit, however it is to be understood that other well known
threshold circuits means may be used. A rectifier and filter
circuit 32B converts the RF voltage from capacitor 30 to a DC level
applied to the Schmidt circuit 32A. Schmidt circuits provide a
signal during the time the input voltage attains or exceeds a
particular magnitude. Thus, when the voltage across capacitor 30 of
FIG. 1 exceeds a particular value an output signal will be
generated by the Schmidt trigger. This output signal is connected
through the enable circuit 34 to the modulator circuit 14. The
enable circuit 34 allows the threshold signal to reach the
modulator circuit 14 only when the electrosurgical unit is set to
be in the coagulation mode. The enable circuit includes an
isolation amplifier 34A of conventional design which is controlled
by the coagulation switch 44. An electromechanical relay or similar
device may be used as an enabling circuit means.
The modulating circuit 14 includes an unijunction transistor 36
connected in an oscillator circuit for generating a sawtooth
voltage, the frequency of which is dependent upon resistor 38 and
capacitor 40. The sawtooth voltage is applied to the base of a high
gain transistor 42. Transistor 42 acts as a switch and is turned on
and off depending upon the base voltage.
Control circuit 16 applies selected bias voltages to the base of
transistor 42 offsetting the sawtooth voltage thereby controlling
the amount of time transistor 42 is on. The magnitude of bias
voltage is selected by a pair of foot switches 44 and 46. Switch 44
is closed for coagulation and switch 46 for cutting. When switch 46
is closed a bias voltage is applied to the base of transistor 42.
The closing of switch 44 supplies a bias voltage to the base of
transistor 42 and 50. The level of the bias voltage from
coagulation switch 44 is determined by a potentiometer 48. As a
safety measure, the closing of coagulation switch 44 turns on a
transistor 50 which short circuits the bias voltage from cutting
switch 46. Thus, the coagulation mode overides the cutting mode.
Furthermore, when the coagulation switch 44 is closed the enable
circuit 34 is enabled allowing the output signal from the threshold
circuit 32 to be conducted through the enable circuit 34 to the
base of transistor 42. The presence of the threshold signal voltage
decreases the on time of transistor 42. In the absence of a
threshold signal the on time of transistor 42 is determined by the
adjustable second bias voltage as controlled by the potentiometer
48.
Amplifier 12 of FIG. 1 includes transistor 12A connected to
transistor 42. The amplifier 12 is enabled only when transistor 42
is turned on. Therefore, it is seen that the RF signal from
oscillator 10 is modulated by transistor 42 and has a pulse width
of substantially the same duration as the on time of transistor 42.
The total pulse repetition time is determined by resistor 38 and
capacitor 40 and remains constant. Therefore, the duty cycle of the
RF pulse is proportional to the pulse width of the threshold
signal.
The pulse control circuit heretofore described automatically
controls the duty cycle of the RF signal in response to active
probe contact with the patient when the electrosurgical device in
coagulation mode. The invention prevents unwanted cutting during
coagulation procedures by reducing the duty cycle and thereby
reducing the average power when the electrosurgical unit is set for
coagulation and when the active probe is not in contact with the
patient. When the active probe is in contact with the patient the
danger of cutting is reduced and the control circuit automatically
increases the duty cycle thereby increasing the average power to
maximize the coagulation effect. During cutting the pulse control
circuit is disabled by setting the control circuit to cutting mode
only so that a continuous wave is supplied to the probes.
In further accordance with the invention, the potentiometer 48 may
be used to manually control the duty cycle without affecting the
amplitude of the RF signal. This method enables the operator to
adjust the electrosurgical unit to provide the minimum power
necessary for coagulation under the operating conditions by using
the lowest possible duty cycle. It has been found that this
procedure reduces unwanted cutting when the electrosurgical unit is
in the coagulating mode. This method may be used independently or
in combination with the automatic pulse control circuit heretofore
described.
* * * * *