U.S. patent number 3,675,655 [Application Number 05/008,549] was granted by the patent office on 1972-07-11 for method and apparatus for high frequency electric surgery.
This patent grant is currently assigned to Electro Medical Systems, Inc.. Invention is credited to Weldon Rex Sittner.
United States Patent |
3,675,655 |
Sittner |
July 11, 1972 |
METHOD AND APPARATUS FOR HIGH FREQUENCY ELECTRIC SURGERY
Abstract
A method and apparatus for electric surgery includes generating
oscillations of high frequency electric energy of substantially
constant amplitude, controlling the duration of and spacing in time
between each series of oscillations generated and applying the
generated energy through an electrode for the purpose of making
surgical incisions and coagulating blood at the point of incision.
A common generator serves as a source of the electric energy for
different surgical procedures, the duration and spacing between
each series of oscillations being closely controlled according to
their intended application and in such a way as to minimize power
requirements and the possible hazards of use either to the doctor
or to the patient.
Inventors: |
Sittner; Weldon Rex (Westport,
CT) |
Assignee: |
Electro Medical Systems, Inc.
(Englewood, CO)
|
Family
ID: |
21732226 |
Appl.
No.: |
05/008,549 |
Filed: |
February 4, 1970 |
Current U.S.
Class: |
606/37;
606/35 |
Current CPC
Class: |
A61B
18/12 (20130101); A61B 18/1206 (20130101); A61B
2018/0066 (20130101) |
Current International
Class: |
A61B
18/12 (20060101); A61b 017/36 (); A61n
003/00 () |
Field of
Search: |
;128/303.14,303.17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
897,961 |
|
Jun 1962 |
|
GB |
|
1,146,989 |
|
Apr 1963 |
|
DT |
|
Primary Examiner: Pace; Channing L.
Claims
What is claimed is:
1. A method for high frequency electric surgery comprising the
steps of:
generating a continuous periodic waveform of high frequency
electric energy wherein within each period of the waveform of the
order of tens of microseconds there is at least one burst of
substantially constant amplitude oscillations of high frequency
electric energy with the duration of the burst being a
predetermined fraction of the period of the waveform; and
continuously applying the generated energy to a body site where a
surgical change is desired in said body site.
2. A method as set forth in claim 1 wherein said electric energy is
oscillating at a frequency of about 0.5MHz.
3. A method as set forth in claim 1 wherein the bursts of high
frequency electric energy are about 10 microseconds in duration and
the time interval between bursts is about 40 microseconds.
4. A method as set forth in claim 1 wherein the bursts of high
frequency electric energy are about 15 microseconds in duration and
the time interval between the bursts of energy is about 20
microseconds.
5. The method of claim 1 wherein said predetermined fraction is in
the order of one fourth, and the generated energy is continuously
applied to said body site when it is desired to coagulate the blood
flowing from said body site.
6. The method of claim 1 wherein said predetermined fraction is in
the order of four sevenths.
7. Electrosurgical apparatus comprising:
generator means for generating a continuous periodic waveform of
high frequency electric energy wherein within each period of the
waveform there is at least one burst of substantially constant
amplitude oscillations of high frequency electric energy with the
duration of the burst being a fraction of the period of the
waveform;
selective control means including an assymetrical waveform
generator for selectively controlling said generator means to
change the fraction of the period in accordance with a desired
surgical procedure;
user operable means for switching on and off when desired, said
generator means; and
electrode means coupled to said generator means for application of
the electric energy generated.
8. The invention recited in claim 7 wherein said generator means is
operable to generate RF energy.
9. The invention recited in claim 7 wherein said electrode means
includes:
an indifferent electrode positioned against a body upon which
surgery is to be performed, and
an active electrode positioned for selectively applying the high
frequency electric energy generated to said body.
10. The invention recited in claim 7 wherein said generator means
includes an RF oscillator circuit having a resonant circuit and
feedback network to sustain oscillations in the resonant circuit,
said oscillator circuit being turned off by said control
multivibrator by disabling said feedback network.
11. The apparatus of claim 7 and including means for changing the
degree of assymetry of the assymetrical waveform.
Description
This invention relates to medical electronic methods and apparatus,
and more particularly to a method and apparatus for conducting
electric surgery in a safe and highly effective manner.
Heretofore, devices have been designed which have employed
radio-frequency (RF) electric energy for performing surgery on the
human body. Typically, such devices included a cutting mode of
operation wherein a continuous waveform of RF energy produced by a
vacuum the generator was used to cut by means of the heat generated
in the body tissue and a coagulation mode wherein a damped RF
energy waveform provided by a separate spark-gap type generator was
used to coagulate the blood flowing from the cut tissues. A
disadvantage with such prior art devices was that in order to
perform the cut/coagulation functions, two separate generators were
required and which applied extremely high voltages to the active
cutting electrode. Consequently, such devices and particularly the
spark-gap generator unduly destroyed the tissue and further
constituted significant hazards in their use both for the patient
and the operating physician.
Accordingly, it is an object of this invention to provide a novel
method and apparatus for cutting tissue and coagulating the blood
at the area of the cut using the same RF generator and
characterized by applying envelopes or packets of RF electric
energy in an oscillatory waveform of substantially constant
amplitude recurring at preselected spaced time intervals.
Another object of the present invention is to provide a novel
apparatus for high frequency electric surgery which obviates the
aforementioned disadvantage of prior art instruments by employing
electric circuitry which enables the use of substantially lower RF
voltages than heretofore possible and provides an essentially
unmodulated oscillatory waveform.
It is another object of the present invention to provide novel
apparatus for high frequency electric surgery as set forth which is
capable of conducting both a cut mode of operation and a
coagulation mode of operation, either simultaneously or
independently of one another.
It is further an object of the present invention to provide a novel
apparatus for high frequency electric surgery characterized by
having an RF generator and control circuitry using solid state
elements which is highly sensitive, reliable and efficient, and has
close power regulation, and is closely adjustable and controllable
in carrying out different selected surgical procedures and
techniques in a safe dependable manner.
In accomplishing these and other objects, there has been provided
in accordance with the present invention electric apparatus for
performing high frequency electric surgery which includes an RF
generator, and a control multivibrator, asymmetrical in operation,
to control the RF generator to provide a combined cut and
coagulation mode, and a coagulation mode of operation. Switching
means are provided whereby the RF generator may be continuously
operated or alternately controlled by the control multivibrator.
The RF generator is connected to amplifying means for amplifying
the RF power or energy generated by the RF generator and applying
it to an active electrode for use in cutting or coagulating living
body tissue. A return means in the form of a patient ground plate
is positioned against the patient below the area of the body to be
operated on for providing a return electric path to the amplifying
means. A power supply means supplies relatively low DC voltages to
the apparatus circuitry. In this way there is provided by a single
electronic oscillator circuit a series of envelopes of RF electric
energy in an oscillatory waveform of substantially constant
amplitude with the envelopes recurring at selected spaced time
intervals for coagulation of blood or combined cutting and
coagulation or the energy in a continuous waveform for the usual
cutting of body tissue.
A better understanding of the present invention may be had from the
following detailed description when taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is partially a block diagram and partially a circuit diagram
of an electric apparatus for high frequency electric surgery in
accordance with the present invention.
FIG. 2 is a circuit diagram of the control multivibrator of FIG.
1.
FIG. 3 is a circuit diagram of the RF generator of FIG. 1.
FIG. 4 is a circuit diagram of the power amplifier of FIG. 1.
FIG. 5 is a circuit diagram of the power supply of FIG. 1.
FIG. 6 is in part a plan view of the patient ground plate of FIG. 1
and in part a circuit diagram of the connection of the patient
ground plate into the circuitry of the electric apparatus of FIG.
1.
FIG. 7 is an illustration of the output waveforms generated by the
apparatus of FIG. 1 in its different modes of operation together
with a comparison of waveforms with a typical spark-gap type
generator.
Referring now to FIG. 1 the electrosurgical apparatus in general is
shown to include a control multivibrator circuit 10 for controlling
an RF generator circuit 20, the output of which is applied to a
power amplifier circuit 30 for increasing the power output together
with a power supply 40 which generates the DC voltage required by
the aforementioned circuits. In FIG. 1, the RF generator 20 is
shown to have a DC voltage supplied to generator terminals 22 and
23, and generator terminal 24 is connected to ground. The DC
voltage applied to the terminals 22 and 23 is derived from the
power supply 40 which generates DC voltages on its output terminals
46 and 48, and output terminal 47 is grounded. A V- voltage,
between terminal 47 and ground may be anywhere in the range of
0-180 volts, and is applied to the generator terminal 23 and to
terminal 22 through a resistor 28. An RF bypass capacitor 29 is
connected between terminal 22 and ground.
The RF generator 20 has a control terminal 21 which is connected to
the fixed contact of one set of relay contacts 100 of the relay
101, hereinafter referred to as the cut relay. A lamp L3 located on
the control panel is connected across relay 101 to indicate when
the apparatus is in the cut mode. The other of the contacts 100 is
a dummy contact while the movable contact arm is connected through
an on-off switch 102 to ground. Switch 102 is hereinafter referred
to as the cut switch and is a toggle type switch located on the
control panel. In the open position shown, the cut mode switch 102
is set for cut 2 and in the closed position it is set for cut
1.
Connected also to the generator terminal 21 is the output terminal
11 of the control multivibrator 10. The control multivibrator 10
has DC voltage supplied to its terminals 14 and 15, the terminal 14
being at ground, and B- voltage from the power supply 40 being
supplied via the circuitry of a patient ground plate or indifferent
electrode 103, to the terminal 15. The B- voltage generated by the
power supply 40 may, for example, be -14 volts. The control
multivibrator 10 has the movable contact arm of relay contacts 104
of the relay 105 connected to its terminal 12. Relay 105 serves as
the coagulate relay and a lamp L2 located on the control panel is
connected across coil 101 to indicate when the apparatus is in the
"coagulate" mode. The multivibrator terminal 13 is connected to the
other fixed contact of the relay contacts 104.
The RF generator 20 is transformer coupled by means of a step-up
power transformer 110 to the power amplifier 30. The generator 20
has its output terminals 25-27 connected to the primary winding of
the transformer 110. The power amplifier 30 has its input terminals
32, 33a, 33b and 34 connected to the transformer 110. V- and ground
are connected to the terminals 31 and 35, respectively, of the
amplifier 30 to supply DC power thereto.
The output of the power amplifier 30 is coupled by a transformer
111 to output lines 112 and 113. The primary of the transformer 111
is connected to amplifier output terminals 36, 37a, 37b and 38. The
output lines 112 and 113 are connected across the secondary winding
of the transformer 111. A resistor 118 is connected between the
output lines 112 and 113 across which is developed the output
voltage of the transformer 111.
The output line 112 is a shielded line having its shield connected
to ground and is connected through DC isolation capacitors 109 and
114 and through a terminal connect 50 to an active electrode 115.
Terminal connect 50 permits the electrode to be plugged into the
control panel of the apparatus. The output line 113 is connected
through a DC isolation capacitor 116 to the two terminal connects
51 and 52 of the patient ground plate 103. A capacitor 117 is
connected between the terminals 51 and 52 for the purpose of
preventing a B- voltage from being supplied to the control
multivibrator terminal 15 whenever the patient ground plate 103 is
not electrically connected to the electrosurgical apparatus at
terminals 51 and 52. Connected to the side of the capacitor 117
adjacent the terminal 51 are a grounded capacitor 120 for DC
isolation and an RF inductive choke 121 for isolating the power
supply 40 from RF energy. A DC isolation capacitor 122 is also
connected to the side of the choke 121 to which B- voltage is
supplied.
The terminals 51 and 52 are mutually connected to a common point
and from that common point are connected through a DC isolation
capacitor 123 to the patient ground plate 103. Connected to the
side of the capacitor 117 common with the terminal 52 is one
terminal of an RF inductive choke 124. The other terminal of the
choke 124 is connected through an RF inductive choke 125 to the
ground plate 103. Connected to the side of the capacitor 117 common
with the terminal 52 is one terminal of an RF inductive choke 124.
The other terminal of the choke 124 is connected through an RF
inductive choke 125 to the line 112 and also the movable contact of
a switch 127. The switch 127 is preferably a treadle switch and
foot-operated by the physician and has fixed contacts 128 and 129,
and is used for switching the mode of operation of the electric
apparatus between "cut" and "coagulate."
The fixed contact 129 of the switch 127 is connected through a
diode 135 to the control multivibrator terminal 15. Similarly, the
fixed contact 128 of the switch is connected through a diode 136 to
the control multivibrator 15. Thus, B- voltage may be supplied to
the terminal 15 through the electrical path defined by the choke
121, terminals 51 and 52, the choke 124, the switch 127, and the
appropriate diode 135 or 136. In this way, the treadle switch 127
cannot actuate the cut or coagulate relays unless the patient plate
103 is plugged into the instrument. A capacitor 137 is also
connected from the switch contact 129 to ground.
The electrical means for connecting the patient ground plate 103 to
the exemplary electrosurgical apparatus additionally includes
terminals 53 and 54, as better illustrated in FIG. 6. The terminals
53 and 54 are shorted together and serve to short out a lamp L4
whenever the plate 103 is connected into the above-described
exemplary apparatus. Terminals 51-54 are shown in FIG. 6 as mounted
on a common plug represented at 55. B- voltage is supplied to the
lamp L4 through a resistor 141. Lamp L4 is preferably located on
the control panel and lit until the patient plate 103 is
electrically plugged into the panel.
Referring now to FIG. 2, the control multivibrator 10 shown
includes a conventional flip-flop circuit with transistors TR5 and
TR6 arranged to alternately conduct and cut-off in a repetitive
sequence. The bases of transistors TR5 and TR6 are connected to
timing capacitors C6 and C5, respectively. A third timing capacitor
C30 is connected between one side of capacitor C5 and terminal 12
so that when terminals 12 and 13 are connected by the actuation of
relay 105 the total capacitance in one side of the flip-flop
circuit is the sum of the capacitance of capacitors C5 and C30
instead of only C5. This shortens the period of conduction of
transistor TR5 and thereby changes the duty cycle for the flip-flop
circuit. Variable resistors R6 and R7 connected to capacitors C5
and C6, respectively, may also be adjusted to vary the duration of
the duty cycle on each side of the flip-flop circuit. Also included
in circuit 10 as shown in FIG. 2 is a transistor TR7 having its
base electrode connected through resistor R10 to the collector of
TR5. The emitter-collector junction of transistor TR7 is connected
between terminal 11 and grounded terminal 14. In this way when
transistor TR5 is conducting, a suitable voltage is applied to the
base of transistor TR7 to cause it to conduct between its emitter
and base electrodes and in effect connect terminal 11 to ground or
zero potential via transistor TR7 which will enable the RF
generator to run for a selected time interval when TR5 is
conducting and be off when TR5 is cut off during the "cut 2" and
"coagulate" modes when terminal 21 is not grounded via contacts 100
and switch 102 as described more fully hereinafter.
Referring now to FIG. 3 the RF generator circuit 20 is shown to
include an RF oscillator circuit 20a transformer coupled by
transformer T2 to a conventional driver amplifier circuit 20b. The
driver amplifier circuit includes a transistor TR9 and functions to
increase the power from the oscillator circuit 20a to the power
amplifier circuit 30 and isolates the oscillator circuit
therefrom.
The oscillator circuit 20a includes a transistor TR8 having its
collector connected to a series resonant circuit of capacitor C28
and winding W1 of transformer T2, with winding W1 having one end
connected to grounded terminal 24. An RF choke CH5 is connected
between the collector and grounded terminal 24 to provide an RF
load for TR8. The emitter of transistor TR8 is connected to the V-
voltage through bias resistors R12 and R28. An RF bypass capacitor
C10 connects between the emitter and ground terminal 24. The base
of the transistor is connected to a regenerative feedback network
including a feedback winding W2 of transformer T2, diode D2, which
rectifies the RF energy induced in the winding W2 together with a
charging capacitor C7 connected between the diode D1 and terminal
22. Resistors R11 and R20 are connected from a mutual connecting
point with diode D1 and capacitor C7 to control terminal 21 and a
control diode D2 is connected between a mutual connecting point
with resistors R11 and R20 and to the V- voltage via resistor
28.
Oscillator circuit 20a will oscillate when terminal 21 is at ground
or zero potential either via contacts 101 and switch 102 or via the
conduction of transistor TR7. When terminal 21, connected to
resistor R20, is at ground or zero potential the feedback network
has sufficient RF energy to enable the resonant circuit to sustain
oscillations. More specifically, when terminal 21 is at ground
diode D2 is back-biased and cannot conduct. This establishes a
timing circuit of C1 and R11 plus R20, the capacitor being charged
by RF energy rectified by diode D1 which will produce sufficient
energy in the feedback network to sustain oscillations. However,
when terminal 21 is not grounded diode D2 will conduct and, with
only R11 and C7 forming the timing circuit for the feedback
network, then there is insufficient RF energy available to sustain
oscillations and the resonant circuit will continue to oscillate
and induce RF power into winding W3 of the driver circuit. Under
these conditions the potential at terminal 21 via diode D2 and
resistor R20 is at the V- voltage and transistor TR7 will now
conduct each time transistor TR5 conducts and cut off each time
transistor TR5 cuts off. In this way the flip-flop circuit operates
continuously when either relay 101 or 105 is actuated but during
the "cut 1" mode the control multivibrator is disabled since its
collector is grounded via contacts 100 and switch 102.
Referring to FIG. 4, there is shown a conventional push-pull
amplifier 30. The amplifier 30 has three serially connected
transistor amplifier stages on each side consisting of transistors
TR1, TR2 and TR3 on one side and transistors TR4, TR10 and TR11 on
the other side. The amplifier 30 operates as a power amplifier to
amplify the RF energy or power generated by the RF generator 20.
The power amplifier is driven relatively hard by the driver
amplifier to achieve the desired performance.
Referring to FIG. 5, the power supply 40 includes input terminals
41 and 42 with an AC electric power source signal generator 200
connected thereacross. The AC electric power source may, for
example, be a conventional 115-volt 60-cycle power source into
which the power supply 40 is connected. The power supply 40 also
includes a conventional power control circuit 199 for varying the
AC input by changing the phase and amplitude thereof and is
commercially sold by General Electric Co. as G.E. TRIAC No. S100B3.
This circuit includes a triac element 201 and a diac or
double-based diode element 202 connected to the control electrode
of the triac element 201. A pair of terminals 43a, 44 are provided
for selectively connecting a variable resistor 203 into the power
control circuit 199 to change its output for the "coagulation"
mode, and similarly a pair of terminals 43b and 45 selectively
connect a variable resistor 204 into the power control circuit 119
to change its output during the "cut" mode. Resistors 203 and 204
are located on the control panel and are preset according to the
desired power for either mode. The terminals 43a and 44 are shown
as stationary contacts which are closed by a movable contact arm of
the relay 105 which is selectively energized for the "coagulate"
mode. Similarly, the terminals 43b and 45 shown as stationary
contacts of relay 101 are selectively closed by a contact arm 59
movable in response to the energization of the relay 101 for the
"cut" mode as shown in FIG. 1. The power control circuit 199 is
also adjustable by means of the variable resistor 205 to vary the
output of the power supply.
Included in the power supply is a transformer 206 which couples the
output of the power source 200 to a diode bridge 207 to provide B-
DC voltage across terminals 47 and 48, and a transformer 208
couples the output of the power control 199 to a diode bridge 209
to provide the V- DC voltage across terminals 46 and 47. A power
switch 211 located on the control panel connects the input power
from the supply 200 to the power control 199 and a lamp L1 serves
to indicate when the power is on to the power supply. A capacitor
212 is connected across terminals 47 and 48 for filtering of the
60-cycle power and a resistor 213 and capacitor 214 are connected
across terminals 46 and 47, the latter also being used to filter
the 60-cycle power to assist in prevention of its being applied to
the electrodes. In this way the waveform of the energy produced by
the RF generator is not appreciably amplitude modulated by the
60-cycle power source 200. Vacuum tube type generators previously
used for the cutting of tissue provide an amplitude modulated
waveform which is modulated by the 60-cycle input power line to the
extent of being completely modulated at 120 cycles. The effect of
such amplitude modulation is to provide a series or envelopes of RF
energy oscillations which decrease to substantially zero amplitude
at one point in each repetition thereof.
In operation, the electrosurgical apparatus of the present
invention as shown in FIG. 1 is in situ with the active electrode
115 positioned to operate on a patient represented at 220. The
indifferent electrode or patient ground plate 103 is placed in situ
against the body of the patient usually with the patient lying on
the plate 103. The power supply switch 211 is turned on and
resistors 203 and 204 are set to the desired power levels. To
perform a cut, the cut switch 102 would then be closed for the "cut
1" mode. The treadle switch 127 would be switched to the "cut"
mode, by the surgeon, thereby connecting the movable contact arm of
the switch 127 to its fixed contact 128 as shown. Thus, the relay
101 is energized closing the terminals 43b and 45 of the power
supply 40 and closing switch 100 to ground terminal 21 of the RF
generator 20 to turn the RF generator 20 "on" to produce a high
frequency electric energy in an oscillatory waveform of
substantially constant amplitude as represented at C in FIG. 7.
This RF electric energy is then amplified by the power amplifier 30
and transformer-coupled to the electrodes 115 and 103. The RF
energy then flows from the active electrode 115 for selectively
cutting the body tissue of the patient 220 and the energy returns
to the plate 103. The RF energy, after passing into the plate 103,
is then dissipated in RF chokes 121, 124 and 125.
After each cutting operation, or periodically in the process of
cutting or surgery, it is necessary to coagulate the blood flowing
from the cut tissues. This is accomplished by operating the treadle
switch 127 thereby to switch the movable contact arm thereof to
fixed contact 129. Relay 101 is de-energized while relay 105 is
energized. Thus, contacts 100 open and terminal 21 is no longer
grounded and contacts 104 close terminals 12 and 13 of control
multivibrator 10 to connect capacitor C30 in parallel with C5. Also
the terminals 43a and 44 of the power supply 40 are closed so that
a higher level of power is generated by the power supply 40 across
output terminals 46 and 47. In the "coagulate" mode the potential
at terminals 11 and 21 alternately changes between two different
electric potential levels with each level being of a selected
duration which is established by the duty or timing cycle of the
flip-flop circuit, and these potential or voltage levels in turn
regulate the time on and time off for the oscillator circuit 20b.
Thus the voltage waveform at the output of the control
multivibrator 10 may be represented by a pulse-shaped waveform B as
shown in FIG. 7. The voltage or potential level to turn the
oscillator circuit on is zero or ground and this occurs as above
described each time transistors TR5 and TR7 conduct. However, when
transistor TR5 cuts off then transistor TR7 in turn cuts off and
the potential at terminals 11 and 21 are a V- voltage supplied via
resistors 28, diode D2 and R20 and this results in shutting the
oscillator circuit off until TR7 again conducts as above described.
Thus the RF energy in the form of a series or envelope of
oscillations are generated by generator 20 as represented at E in
FIG. 7 for each on-time for transistors TR5 and TR7, this RF energy
or electric power being amplified by the power amplifier 30 and
applied to electrodes 115 and 103. This RF electric energy may be
characterized as envelopes or packets of a relatively short
duration and recurring at regular intervals and operates through
the active electrode 115 to coagulate the blood flowing from the
severed blood vessels along previously cut body tissue.
A third mode in which this apparatus may be used is called "cut 2"
and in actuality is a mode whereby the active electrode 115 both
cuts and coagulates. In the "cut 2" mode the treadle switch 127 may
remain in the cut position to retain the energization of relay 101
and the cut power at terminals 46 and 47; however, switch 102 is
placed in the "cut 2" position which opens the ground circuit to
terminal 21. In this way the control multivibrator 10 controls the
enabling or on-time for the RF generator 20 and the disabling or
off-time for the RF generator in the same manner as above described
with reference to the "coagulate" mode. However terminals 12 and 13
of the control multivibrator 10 are open and capacitor C30 is
removed so that the on-time is longer and the off-time is shorter
as represented by waveform A in FIG. 7. The RF generator will then
produce a series of envelopes of RF energy oscillations of a longer
duration with shorter time intervals between each series, said
energy being amplified and applied to the electrodes 115 and 103.
This RF energy on the active electrode 115 effects partially a
cutting and partially a coagulating action on the body tissue of
the patient 220.
Reference is now made to the waveforms of FIG. 7 to explain the
advantages of the present invention: The electrical resistance of
the body tissue through which the RF current flow is essentially a
resistance impedance and therefore the waveforms of the RF current,
RF voltage and instantaneous RF power or energy are essentially the
same as represented by waveform C, and may be characterized by
being oscillatory and of a substantially constant amplitude. A
preferred frequency of this RF energy is 0.5MHz so that the period
of each cycle is the reciprocal of the frequency or equal to 2
microseconds. The duration of the "on-time" and the "coagulate
mode" is about 10 microseconds an a time interval of the off-time
of about 40 microseconds or a 1-to-4 ratio has been found to
provide excellent blood coagulation results. Accordingly, this
produces a series of oscillations of RF electric energy of the same
duration and recurring at regular intervals as represented by
waveform E. The terms "envelope" or "Packet" as used herein are
therefore intended to refer to a series of RF energy oscillations
which occur during a particular duration or preselected time
interval. Since the oscillations produced by generator 20 are of a
substantially constant amplitude, the positive and negative peaks
define a rectangular area which may be considered an essentially
rectangular shaped envelope of RF energy. This is to be
distinguished from an RF energy produced by a spark-gap type
generator which has damped oscillations and the instantaneous power
of which decreases rapidly as represented in FIG. 7 by waveform
G.
The significance of the difference between the two is best
understood by considering the average power waveforms for the two
types of generators as represented by waveforms F and H. The
generator 20 producing a series or envelopes of RF power E has an
essentially flat average power characteristic over the duration of
the envelope as represented at F, whereas that of the spark
gap-type generator rapidly decreases to zero along a parabolic
shaped curve of progressively decreasing slope as represented at H.
Therefore in order to provide equivalent average power over a
similar duty cycle, the spark-gap generator requires considerably
higher RF voltages and currents.
Comparative tests have shown that the instrument above described
will operate at about 2,400 volts peak-to-peak at the active
electrode whereas a comparable spark-gap type generator requires
about 6,500 volts peak-to-peak. This difference in operating
voltages is an important factor from the standpoint of the safety
of the patient, personnel and surgeon. Further, the AC power input
to the vacuum tube type oscillator generator is usually on the
order of 1,000 volts at 60 cycles as compared to the 117 volts for
the "cut 1" mode in the present apparatus and the DC power of about
1,000 volts for the vacuum tube type generator as compared to the
maximum of 180 volts in the exemplary apparatus.
The average power of the exemplary apparatus to meet cutting power
and peak coagulating power requirements is about 500 watts and 700
to 800 volts maximum or peak. The output of the RF generator 20 of
the exemplary apparatus is in the range of about 0-300 volts for
the "cut 1" mode and about 0-400 volts for the "cut 2" and
"coagulate" modes. In turn, the output voltage at the active
electrode is in the range of about 0-1.1 KV for the "cut 1" mode
and about 0-1.5 KV for the "cut 2" and "coagulate" modes. These
ratings compare to a peak voltage for coagulate in the spark-gap
generator of about 4.5 KV and peak power of about 6.5 KW.
In addition, the solid state elements employed herein provide a
circuit of much improved reliability and efficiency and closer
power regulation over high frequency electrosurgical instruments
heretofore provided. The relatively low DC voltage of -14 volts
used as the bias voltage for the transistors and for the treadle
switch 127 which is preferably "explosion proof" adds to the
safety. In the above described circuitry the DC voltage and
60-cycle power line voltage are effectively isolated from the
electrodes to minimize modulation of the main power 60-cycle
frequency which would otherwise affect the RF generator output and
for patient safety.
Although the present invention has been described with a certain
degree of particularity, it is understood that the present
invention has been made by way of example and that changes in
details of structure may be made without departing from the spirit
thereof.
* * * * *