Electrosurgical unit

Abstract

An electrosurgical unit for generating electrical signals intended for application to the body of a patient via an electrosurgical electrode, is disclosed. Cutting signals and coagulation signals, as well as a blend of both signals, are generated by the unit under the control of a mode control circuit that is responsive to the operation of selector switches and/or manually operated actuators. Selected patient and unit conditions are monitored to have the electrosurgical unit disabled under certain dangerous conditions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to electrosurgical units. More specifically, the present invention concerns an improved electrosurgical unit that operates to generate high power electrical signals for use in performing electrosurgery.

2. Description of the Prior Art

A variety of electrosurgical units are available in the prior art. These units function to permit surgical cutting and/or coagulation electrically. Three different signals are characteristically generated and used. These signals may be referred to as cutting signals, coagulation signals, or blended signals formed by combining both the cutting and coagulation signals. Such signals are applied to a patient, conducted through the patient's body, and returned to the unit via a ground path provided by an "indifferent" pad that is maintained in contact with the patient.

Generally described, the cutting signal is a high frequency signal that serves to cut when applied to a patient. An electrosurgical electrode is used to apply the electrical energy to definitely defined and concentrated points of a patient's body. As is well known, cutting is accomplished by the concentrated application of high frequency electrical energy which effectively destroys the body cells directly beneath the electrosurgical electrode.

Coagulation signals are intended to produce coagulation by shrinking vessel walls. Typically such coagulation signals are pulses of energy having a damped sinusoidal waveform. Generally, coagulation signals may be viewed as causing cell dehydration to produce coagulation rather than destroying cells in the fashion of cutting signals.

Blended signals formed by combining cutting and coagulation signals are useful for accomplishing cutting and coagulation at the same time. Alternating periods of each signal may be used to form the blended signals.

As may be readily appreciated, the application of large amounts of electrical power to a human body presents the potential for serious burning. Consequently, the power level of electrosurgical signals must be accurately controlled.

Prior art units are generally not as stable and readily controllable as is desirable to promote maximum safety. The reason is that "tube" type circuits have been necessarily used to produce the cutting and coagulation signals due to the high power levels involved, i.e., 450 watts output, and the inability to generate the earlier mentioned damped sinusoidal pulses with solid-state circuits.

As is well known, such tube-type circuits vary in output power as a function of the condition and age of the tubes, i.e., as the tubes age and deteriorate the output power changes.

Such aging of electronic tubes is continuous and consequently the power generated by such circuits also is continually changing to effectively frustrate stability and accurate control. As a result, a not uncommon result is over or under coagulation with the attendant medical complications.

It is thus the intention of the subject invention to provide an improved electrosurgical unit that overcomes the disadvantages of prior art units by providing a greater amount of electrical power for electrosurgical use than heretofore possible, being stable and accurately controllable, being compatible with solid state technology, and being of reduced size and weight to more readily permit repositioning of the unit by medical personnel.

SUMMARY OF THE INVENTION

Briefly described, the present invention involves an electrosurgical unit for providing cutting, coagulation and blended signals suitable for use in performing surgical cutting or coagulation or a combination of both.

More particularly, the subject electrosurgical unit includes circuitry for providing high frequency, high power electrical signals for cutting, pulses of said high frequency signals for coagulation, and a blend of the two signals when desired. Generation of each of the signals is controlled by mode control and selection circuitry that is in turn responsive to hand or foot operated actuators. Output level control circuits are used to permit control of the amplitude level of the cutting and coagulation signals individually. Circuits for continually monitoring certain patient and unit conditions may be connected to disable the electrosurgical unit in response to the detection of undesired conditions.

The objects and many attendant advantages of the present invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description which is to be considered in conjunction with the accompanying drawings wherein like reference symbols designate like parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram generally illustrating an electrosurgical unit in accordance with the present invention.

FIG. 2 is a schematic block diagram illustrating exemplary drive and mode control circuitry that may be used in conjunction with the present invention.

FIG. 3 is a schematic block diagram illustrating exemplary circuitry that may be used to provide mode control signals in accordance with the present invention.

FIG. 4 is a schematic diagram illustrating an exemplary electrode monitoring arrangement that may be used in conjunction with the present invention.

FIG. 5 illustrates exemplary level control and output amplifier circuits that may be used in conjunction with the present invention.

FIG. 6 is a graphic diagram illustrating a number of waveforms that are useful in describing the operation of the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, an electrosurgical unit in accordance with the present invention essentially includes a push-pull amplifier 10 that is connected to be driven by pulses provided by a drive circuit 12. Output signals provided by the amplifier circuit 10 are applied through a coupling transformer 14 to a pair of output terminals 16. Any conventional electrosurgical electrode (not shown) may be connected to the terminals 16 for applying electrical energy to a patient. The level of the output signals provided by the amplifier 10 are controlled by an output level control circuit 18 that is selectively operated in response to mode selection signals provided from a mode selection circuit 20. Such mode selection signals are also applied to a mode control circuit 22 to have appropriate drive pulses developed by the drive circuit 12. manually operated actuators 24 may be connected to the mode selection circuit 20 for controlling the output of such mode selection signals. Selected monitoring circuits 26 may be connected to provide alarm signals which disable the electrosurgical unit.

Referring briefly to the waveforms of FIG. 6, cutting signals provided by an electrosurgical unit in accordance with the invention involve high frequency, high power signals. As an example, the cutting signals illustrated by waveforms A may have a frequency of 250kHz. The output power may be controlled to be as high as is necessary to perform the desired cutting. For example, an electrosurgical unit has been designed to provide up to 600 watts of cutting power.

Coagulation signals, as illustrated by waveform B, involve short pulses, or bursts, of the high frequency signals used for cutting. The power level of coagulation signals is usually decreased considerably from the level that is used for cutting. As an example, it has been empirically found that 25 microsecond pulses of high frequency energy occurring at 75 microsecond intervals will efficiently produce coagulation.

Blended signals, as illustrated by waveform C, are formed by including alternate periods of cutting signals and coagulation signals. As shown, a 10 millisecond duty cycle may be used wherein coagulation signals are provided for 2.5 milliseconds and cutting signals are provided for 7.5 milliseconds. The blended signals would be used to produce coagulation as cutting progresses.

Referring again to FIG. 1, the 250kHz high frequency signals are provided by the amplifier circuit 10 in response to drive pulses that are provided by the drive circuit 12. The coagulation signals are provided by allowing the drive circuit 12 to operate for 25 microsecond periods and be disabled for 75 microsecond intervals following each operation period of 25 microseconds. The blended signals would be produced by alternately operating the drive circuit 12 between the cut mode and the coagulation mode. The different amplitude levels to be used for the cutting and coagulation signals are independently controlled by the output level control circuit 18 in a manner described in greater detail hereinafter.

An exemplary drive circuit 12 and mode control circuit 22 is illustrated by FIG. 2. As shown, a 500kHz multivibrator circuit is connected to provide pulses to clock a flip-flop circuit 30. The pulses provided by the multivibrator 28 are illustrated by waveform H of FIG. 6 wherein 0.5 microsecond pulses occur every 2 microseconds. The output signals at the Q and Q output terminals 32 and 34, respectively, of the flip-flop 30 alternately change between high and low levels with each succeeding pulse from the multivibrator as shown by waveforms J and K of FIG. 6.

For the purposes of this application, a NAND gate as hereinafter referred to is understood to provide a high output signal whenever any of its inputs is a low signal and provide a low output signal only when all input signals are high.

The output terminals 32 and 34 of the flip-flop 30 are connected as one of two inputs to a pair of NAND gates 36 and 38, respectively. The pulses from the multivibrator 28 are applied as a second input signal to the NAND gates 36 and 38 via a NAND gate 40 which effectively serves as an inverter as may be observed from the waveforms H and I of FIG. 6.

Assuming that the enabling input signal applied to the J input terminal of the flip-flop 30, and to the NAND gate 40 is continually high, the output of the NAND gate 40 will be high for the time interval between successive pulses from the multivibrator 28 and low for the duration of each of the multivibrator pulses as shown by waveform I. Consequently, the NAND gates 36 and 38 will alternately provide low signals for the periods between successive pulses from the multivibrator 28 as shown by waveforms L and M, respectively. Otherwise considered, each of the NAND gates 36 and 38 will produce negative pulses at a 250kHz rate which, when applied to drie the push-pull amplifier circuit 10 as described in greater detail in conjunction with FIG. 5, will produce the desired 250 kHz high frequency signals.

As earlier discussed, the coagulation signals may be simply viewed as pulses, or bursts, of the 250kHz high frequency signal that is used as a cutting signal wherein the bursts last for 30 microseconds and occur every 100 microseconds. Referring to FIG. 2, this is accomplished by effectively cyclically disabling the flip-flop 30 for periods of 75 microseconds every 100 microseconds. This would require that the J input terminal of the flip-flop 30 alternately rerceive a low signal for a period of 75 microseconds followed by a high signal for a period of 25 microseconds. To this end, a multivibrator 42 is connected to provide 25 microsecond pulses at 100 microsecond intervals as shown by waveform N of FIG. 6. Such pulses from the multivibrator 42 are applied through a pair of serially connected NAND gates 44 and 46, and a flip-flop 48, to the J input terminal of the flip-flop 30. The NAND gates 44 and 46 serve to permit controlled application of the pulses from the multivibrator 42 to the flip-flop 30 as is hereinafter explained. Synchronism of cutting and coagulation signals is provided by having the flip-flops 30 and 48 both clocked by the multivibrator 28.

Assuming that a high signal is provided to the respective NAND gates 44 and 46 at the respective input leads 52 and 54 thereof, the pulses from the multivibrator 42 will pass through both the gates 44 and 46. However, if a low input signal is applied to the NAND gate 44 via the lead 52, the pulses from the multivibrator 42 will be effectively blocked since the output of the NAND gate 44 will be maintained high regardless of the level of the signal applied thereto from the multivibrator 42. Accordingly, high signals are applied to the gates 44 and 46 via the leads 52 and 54, respectively, whenever coagulation signals are to be provided while a low signal is applied to the gate 44 whenever a coagulation signal is not desired. Similarly, a low signal is applied to the gate 46 when cutting signals are desired to have the flip-flop 30 and 48 set and reset by the pulses from the multivibrator 28.

The above-described signals applied to the gates 44 and 46 via the leads 52 and 54, respectively, are provided in response to coagulation and cutting mode selection signals appearing at the leads 56 and 58, respectively. The coagulation mode selection signal applied to the lead 56 will be low as will be the cut mode selection signal when applied to the lead 58. The leads 56 and 58 will receive high signals at all other times when no mode selection signals are present.

The coagulation mode selection signal appearing at the lead 56 is applied as an input to a NAND gate 60 to have the desired high input signal applied to the NAND gate 44 via the lead 52 during the coagulation mode. Similarly, a cut mode selection signal is applied to a NAND gate 62, and an inverter 64 connected in series therewith, to have the desired low signal applied to the NAND gate 46 via the lead 54 during a cutting mode.

Desired blended signals are generated by alternately applying low signals to the NAND gates 60 and 62 from a pair of NAND gates 66 and 68, respectively. This is accomplished in accordance with the earlier described timing sequence (see waveform C) by having the NAND gate 66 provide a low signal to the gate 60 for a period of 2.5 milliseconds for the coagulation period followed by having the NAND gate 68 provide a low signal to the gate 62 for a period of 7.5 milliseconds for the cutting period. The gates 66 and 68 are connected to receive a high input signal via an inverter 70 when a blend mode selection signal is applied to the inverter via the lead 72. The desired timing sequence is controlled by input signals applied to the NAND gates 66 and 68 from a timing circuit including a multivibrator 74. Pulses occurring at a rate of 400Hz are provided by the multivibrator 74. A pair of dividers 76 and 78 may be used to provide pulsed signals having reduced rates of 200Hz and 100Hz at the respective output terminals 77 and 79, thereof. Such 200Hz and 100Hz signals are illustrated by waveforms O and P.

As shown by waveform O, the 200Hz pulsed signals provided by the divider 76 include 2.5 millisecond pulses occurring at 5 microsecond intervals while the 100Hz signal includes 5 millisecond pulses occurring at 10 millisecond intervals. When such 200Hz and 100Hz signals are applied as inputs to a NAND gate 80 via the leads 77 and 79, the output of the gate 80 will be cyclically maintained high for 7.5 milliseconds and low for 2.5 microseconds as shown by waveform Q of FIG. 6. An inverted waveform is provided by an inverter circuit 82 as shown by FIG. 6, waveform R. The respective outputs of the NAND gate 80 and the inverter 82 are applied as inputs to the NAND gates 68 and 66 via leads 81 and 83. The gate 68 thus applies a low signal to the gate 62 to have cutting signals generated for a period of 7.5 milliseconds followed by the NAND gate 66 applying a low signal to the gate 60 to have coagulation signals generated for a period of 2.5 milliseconds.

The three mode selection signals necessarily applied to the leads 56, 58 and 72, to operate the mode control circuit 22 to have desired cutting, coagulation or blended signals generated, are provided from the mode selection circuit 20 in response to operation of the actuators 24.

An exemplary foot operated actuator may involve an arrangment of three individual pedals, or the like, which ultimately cause a desired mode selection signal to be provided at the appropriate one of the leads 56, 58 and 72 when a pedal is depressed or otherwise operated. Such foot operated actuators are well known and a detailed discussion of such actuators is not deemed necessary for the purpose of this description. A hand operated actuator may be used to perform the same functions.

As shown by FIG. 3, the mode selection circuit 20 includes a bank of mechanical switches 84 that are manually operable and which serve to pass or stop signals provided by operation of the foot actuators 24. For example, four switch positions may be provided for CUT ONLY, COAGULATION ONLY, BLEND ONLY, and CUT-COAGULATE-BLEND. In the first three positions, only operation of the mode pedal corresponding to the position of the switch 84 will be effective. In the last position any pedal may be effectively operated.

The selection switch 84 may simply involve opening the conductive path for non-selected modes and closing the conductive path for the selected mode. For example, where only the cut mode is desired, the switches 84 would be placed in the CUT ONLY position. The circuit for the cut mode would be closed while all other switches would be open.

The signals provided by the actuators 24 via the mode selection switches 84 are applied to an array of NAND gates that are essentially connected to form a decoder. As shown in FIG. 3, a cut mode selection signal would appear at the lead 58 at the output of a NAND gate 86 whenever certain input signals summarized by the equations appearing in FIG. 3 are applied. For Example, the equation CUT = CT.sup.. CG.sup.. ALARM indicates that the desired low level cut mode selection signal will be provided by gate 86 in response to the simultaneous application of input signals representing a cut signal, a lack of a coagulation signal, and a lack of an alarm signal. The cut signal would be high and would be provided via an inverter 88. The signal indicating the lack of a coagulation signal and the lack of an alarm signal is provided at the output of an inverter 90 which is connected to receive the output of a NAND gate 92 connected to receive as inputs a high signal via a lead 94 representing CG and a high signal via a lead 96 representing the lack of an alarm condition (ALARM).

Similarly, a blend mode selection signal is provided at the lead 72 at the output of a NAND gate 98 and a coagulation mode selection signal is provided at the lead 56 at the output of a NAND gate 100 in accordance with the equations shown in FIG. 3.

As may be noted, the ALARM signal may be directly applied to each of the NAND gates 86, 98 and 100 as a high level signal under normal non-alarm conditions. This high level signal permits the respective NAND gates 86, 98 and 100 to respond in a routine fashion to any low level signals applied thereto. However, should an alarm condition occur, the ALARM signal is replaced by a low ALARM signal which would be applied to each of the NAND gates 86, 98 and 100. The result is that each of these gates 86, 98 and 100 will provide a high output signal regadless of the presence or absence of any mode selection signals. The result is that the electrosurgical unit is effectively disabled until the ALARM signal is removed by the detected dangerous condition being remedied.

Any number of inherently dangerous conditions may be monitored and used to generate an ALARM signal which disables the electrosurgical unit. Exemplary of such monitoring schemes would be a heat transducer situated within the unit itself to monitor the temperature of certain component elements of the unit to detect when the temperature is at a level dangerous to to components and to the unit. For example, the temperature of a power transformer may be monitored to prevent overheating and consequent damage to circuit components.

A heat transducer circuit 102 is illustrated in FIG. 3 and is intended to provide a high signal at an output lead 104 under normal ambient conditions and a low signal whenever the temperature is detected to be at a predetermined dangerous level. Any conventional heat transducer circuit may be used. When the low signal is applied via the lead 104 as an input to a NAND gate 106, a corresponding low output signal is provided at the output of an inverter 108 as an ALARM signal.

Another dangerous condition that may cause serious injury to a patient is an imbalance in the amount of current flowing from the electrosurgical unit through an active conductor to the electrosurgical electrode and the current flowing from the indifferent pad through ground conductor to a ground terminal of the unit. Under normal conditions the amount of current flowing through these two conductors is equal. An imbalance may indicate that current applied to the patient is exiting through a path other than the desired path provided by the indifferent pad. An example would be where the indifferent pad is not in proper contact with the patient and/or the patient is improperly grounded by having some part of the body in contact with an item such as the operating table at ground potential.

To detect such a dangerous condition, a current monitor 110 may be provided to generate an ALARM signal which is also applied to the NAND gate 106 as a low level signal to disable the electrosurgical unit in the manner previously described.

An exemplary current monitoring circuit is illustrated by FIG. 4. As shown, an active conductor 112 connected to an electrosurgical electrode and a ground conductor 114 connected to an indifferent pad may be wound about a toroidal core 16. A sensing winding 118 is also wound about the toroidal core. Unequal amounts of current flow through the conductors 112 and 114 will result in current flow through the sensing windings 118. A current detector 120 of conventional design is connected to the windings 118 to detect the current flow therein and respond by providing a low output signal to a latching circuit 124 via an output lead 122. In the exemplary circuit of FIG. 4, the current detector 120 may be of the type that will provide an output signal whenever the current flow through the windings 118 exceeds a selected threshold current level.

The latching circuit 124 is of a conventional type including a pair of NAND gates 126 and 128. The application of a low signal to the NAND gate 126 via the lead 122 causes the output of the gate 126 to be high. This high output of the gate 126 when applied as an input to the gate 128, along with a high reset signal at the lead 129, will cause the output of the latching circuit 124 at the terminal 130 to be low. As is typical of the illustrated latching circuit 124, the output appearing at the terminal 130 will remain low until a low reset signal is applied to the gate 128 to reset the latching circuit. If the reset signal used is a momentarily low signal (a negative pulse), the output signal at the terminal 130 will remain high (return to normal) only if the alarm condition has been removed and the signal at the lead 122 is high. If a low signal continues to bbe applied as an input to the NAND gate 126 via the lead 122, the output of the latching circuit will revert to a low signal after removal of the reset signal. As such, the electrosurgical unit may not be artificially reset to be made operative, without correction of the dangerous condition.

From the foregoing discussion, it is now apparent that operation of the foot actuators 24 will cause mode selection signals to be provided by the mode selection circuit 20 for controlling the mode control circuit 22, and the level control circuit 18, such that the driving pulses illustrated by waveforms L and M of FIG. 6 will be applied from the NAND gates 36 and 38 at the output leads 136 and 138, respectively, to drive the push-pull amplifier circuit 10.

Referring now to FIG. 5, the push-pull amplifier circuit 10 may be observed to basically include a conventional transistorized push-pull amplifier circuit including complementary circuit halves formed by serially connected transistors Q1, Q2, Q3, and Q1', Q2', Q3'. The series connected amplifying transistors Q1 and Q2 are driven by the transistor Q3 which is in turn driven by an output transistor Q4. Similarly, the transistors Q1' and Q2' are driven by the transistor Q3' which receives drive signals at the base thereof from an output transistor Q4'. The drive transistors Q3 and Q3' are alternately driven in unison with the output transistors Q4 and Q4', respectively, in response to the application of the pulses from the respective NAND gates 36 and 38 to the output gates 132 and 134 via leads 136 and 138, respectively.

The gates 132 and 134 as well as the gates 140 and 142 to be later discussed, are of a conventional type wherein the application of prescribed low signals thereto enable the gates.

Referring again to the waveforms of FIG. 6, the negative output pulse applied from the gate 36 (waveform L) will enable the gate 132 and thereby permit current flow through the primary coil of a coupling transformer 133. The transistor Q4 will be rendered conductive by the resulting voltage across the secondary coil of the transformer 133 to have a positive drive voltage (shown by waveform F) applied to the base of the transistor Q3 from an accurately controlled voltage source including a transistor Q5. The transistors Q3, Q2 and Q1 will thus be rendered conductive as is illustrated by waveform D of FIG. 6. Similarly, the negative pulses from the NAND gate 38 (see waveform M) will enable the gate 134 to permit current flow through the primary coil of a coupling transformer 135. The transistor Q4' will thus be rendered conductive and positive drive signals will be applied to the base of the transistor Q3'. The transistors Q3', Q2' and Q1' will thus be rendered conductive and non-conductive (as shown by waveform E) at alternte time intervals with the transistors Q3, Q2 and Q1. An essentially sinusoidal waveform is provided at the output terminals 16 via the output transformer 14 in that harmonics are for the most part eliminated in the operation of the amplifier 10.

The push-pull amplifier 10 may be provided with an appropriate number of capacitors 144 to provide filtering of any high frequency ripple from the power supply connected thereto. It is to be understood that although only series of two amplifying transistors Q1 and Q2 and Q1' and Q2' have been illustrated, that each half of the push-pull amplifier 10 may include a series of as many transistors as is required to satisfy desired output power requirements of a unit. For example, it has been found that as many as eight transistors may be readily connected in parallel in the manner exemplified by the transistors Q1 and Q2 or Q1' and Q2' to provide an output power level of 600 watts.

The amplitude level of the signals provided at the output terminals 16 are controlled by a cut level control circuit including a transistor Q6 for cut signals and a coagulation level control circuit including a transistor Q7 for coagulation signals. The level control circuits also include variable resistors 146 and 148 which are respectively connected to control the base voltage of the transistors Q6 and Q7. Each of these resistors 146 and 148 is of the type that may be manually adjusted by a user of an electrosurgical unit. As shown, the gates 140 and 142 are connected to be enabled by the application of mode selection signals from the NAND gate 64 and the interver 60, respectively. Accordingly, the cut and coagulation level control circuits will be operative only during the periods of time during which cutting or coagulating signals to be controlled are being provided at the output terminal 16.

As earlier mentioned, the transistor Q5 is connected to function as an accurate voltage source that provides bias voltage to the collectors of the output transistors Q4 and Q4'. The bias voltage provided by the transistor Q5 is controlled by the operative one of the two level control circuits including the transistors Q6 and Q7.

The amplifier 10 is operated in a non-saturated mode by a pair of feedback leads 150 and 152 that are respectively connected between the nodes 154 and 156, at the ends of the primary coil 158 of the output transformer 14, and the cathode of a zener diode 160. As the voltage at the nodes 154 and 156 approaches a voltage level set by the zener diode 160, i.e., 3 volts, a transistor Q8 having its base connected to the zener diode 160 is rendered conductive. The transistor Q5 is hence rendered non-conductive and the transistors Q4 and Q4' cease providing additional drive voltage to the base of the transistors Q3 and Q3', respectively. The transistor Q9 is briefly rendered conductive and acts to drain any residual voltage stored on the energized one of the secondary coils of the coupling transformers 133 and 135.

Any suitable power supply circuit may be used with the subject invention to provide the required biasing and other indicated voltges. Needless to state, the multivibrator circuits 28, 42 and 74 may be of any conventional type wherein the duration and frequency of pulses provided may be adjusted as desired.

A capacitor 162 is illustrated as being connected in one of the leads to the output terminals 16. Such a capacitor 162 provides D.C. isoltion to prevent the application of direct current to a patient and thereby preclude unexpected muscular reactions by a patient undergoing electrosurgery.

From the foregoing description, it is now clear that the present invention provides an improved electrosurgical unit that provides output signals for which the voltage levels are consistent, accurately controllable, and not subject to degradation and fluctuaton resulting from deterioration of included electronic tubes.

While a preferred embodiment of the present invention has been described hereinabove, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense and that all modifications, constructions and arrangements which fall within the scope and spirit of the invention may be made.

Claims

What is claimed is:

1. An electrosurgical unit for generating electrical signals to be applied to the body of a patient by an electrosurgical electrode for producing surgical cutting and coagulation as selected, said electrosurgical unit comprising:

a pair of output terminals adapted to be coupled to the electrosurgical electrode;

first means for providing a continuous alternating current cutting signal having a selected freuency that produces surgical cutting when applied to the body of a patient;

second means for cyclically disabling said first means to provide a coagulating signal that is a succession of bursts of said alternating current signal, said coagulating signal providing coagulation when applied to the body of a patient;

third means for altering the disabling cycle of said second means to extend the length of time said first means operates and to provide a blended signal that alternately produces cutting and coagulation when applied to the body of a patient; and

output means for applying the blended signal to the output terminals.

2. The electrosurgical unit defined by claim 1, said first means including:

drive means for providing drive pulses at a pulse rate corresponding to the frequency of said alternating current signal; and

wherein the output means is responsive to said drive pulses for providing said alternating current signal at the output terminals.

3. The electrosurgical unit defined by claim 2, said drive means including:

a first multivibrator for providing pulses at a rate that is twice said selected frequency;

a bistable means having two states and producing output signals corresponding to each of two states thereof, said bistable device being switched between said two states in response to said pulses from said first multivibrator; and

gating means connected to be responsive to said first multivibrator pulses and to the output signals of said bistable device for providing said drive pulses.

4. The electrosurgical unit defined by claim 3, said gating means including:

first and second NAND gates each receiving from said bistable device an output signal corresponding to a different one of said two states; and

a third NAND gate connected to be responsive to said first multivibrator for simultaneously providing to said first and second NAND gates an input signal corresponding to an inversion of said pulses from said first multivibrator.

5. The electrosurgical unit defined by claim 3, said second means including a second multivibrator connected to distable said bistable device for predetermined time periods at predetermined time intervals, said bistable device being prevented from providing said drive pulses to said gating means when disabled.

6. The electrosurgical unit defined by claim 5, said third means including means for alternately permitting and preventing, in accordance with a predetermined timing sequence, said second multivibrator from disabling said bistable device for said predetermined time periods at said predetermined time intervals.

7. The electrosurgical unit defined by claim 2, further including inductive coupling means for providing said drive pulses to said output means.

8. The electrosurgical unit defined by claim 2, said output means including:

a transistorized push-pull amplifier responsive to said drive pulses; and

a coupling transformer for inductively coupling the output of said push-pull amplifier to said output terminals.

9. The electrosurgical unit defined by claim 8 further including mode selection means for providing mode selection signals to control the operation of said first, second, and third means to provide cutting signals, coagulation signals, or blended signals.

10. The electrosurgical unit defined by claim 9, further including manually operable actuator means for controlling the selection and generation of desired signals by said unit.

11. The electrosurgical unit defined by claim 8, wherein the push-pull amplifier includes a pair of inputs and an output and wherein the output means includes feedback means coupled between the output and inputs of the amplifier for altering the voltage level at the inputs of said amplifier in accordance with the voltage level at the output thereof to prevent said amplifier from attaining a saturated mode.

12. The electrosurgical unit defined by claim 8, wherein the output means includes a cut level control means and a coagulation level control means for individually controlling the gain of the push-pull amplifier to thereby control the amplitude of the output signal, said cut level control means and said coagulation control means being respectively operated in response to the application thereto of mode selection signals corresponding to cutting and coagulating signals, respectively.

13. The electrosurgical unit defined by claim 12, further including monitoring means for disabling said electrosurgical unit in response to the detection of unequal amounts of current flowing to and from a patient with respect to said unit.

14. The electrosurgical unit defined by claim 12, further including means for monitoring the temperature of said electrosurgical unit to disable said unit in response to said temperature thereof exceeding a selected temperature.

15. The electrosurgical unit defined by claim 14, said drive means including:

a first multivibrator for providing pulses at a rate that is twice said selected frequency;

a bistable means having two states and producing output signals corresponding to each of two states thereof said bistable device being switched between said two states in response to said pulses from said first multivibrator; and

gating means connected to be responsive to said first multivibrator pulses and to the output signals of said bistable device for providing said drive pulses.

16. The electrosurgical unit defined by claim 15, said second means including a second multivibrator connected to disable said bistable device for predetermined time periods at predetermined time intervals, said bistable device being prevented from providing said drive pulses to said gating means when disabled.

17. The electrosurgical unit defined by claim 16, said third means including means for alternately permitting and preventing, in accordance with a predetermined timing sequence, said second multivibrator from disabling said bistable device for said predetermined time periods at said predetermined time intervals.

18. The electrosurgical unit defined by claim 17, further including inductive coupling means for providing said drive pulses to said output means.

19. The electrosurgical unit defined by claim 1 further including actuator means for controlling the selection and generation of said cutting signals, coagulating signals, and blended signals in response to manual manipulation of said actuator means.

20. The electrosurgical unit defined by claim 19, further including mode selection means for generating mode selection signals in response to operation of said actuator means, said mode selection signals being applied to control the operation of said first, second and third means to have selectively provided said cutting signals, coagulating signals, and said blended signals.

21. The electrosurgical unit defined by claim 1, further including monitoring means for disabling said electrosurgical unit in response to the detection of unequal amounts of current flowing to and from a patient with respect to said unit.

22. The electrosurgical unit defined by claim 1, further including means for controlling the output amplitude of said cutting signals and said coagulating signals.

23. The electrosurgical unit defined by claim 1 wherein the output means includes level control means for providing the independent adjustment of the amplitude level of the cutting and coagulating components of the blended signal.

24. The electrosurgical unit defined by claim 23 wherein the level control means includes means for manually adjusting said level control means.

25. The electrosurgical unit defined by claim 24 wherein said third means includes means to provide a blended signal in which the cutting component has a time duration of approximately three times the time duration of the coagulating component.

26. An electrosurgical unit for generating electrical signals to be applied to the body of a patient by an electrosurgical electrode for producing surgical cutting and coagulation, the electrosurgical unit comprising:

first means for generating a high frequency cutting signal for producing surgical cutting when applied to the body of a patient;

second means for generating a succession of bursts of a high frequency signal for providing a coagulating signal which produces coagulation when applied to the body of a patient;

a pair of output terminals adapted to be coupled to the electrosurgical electrode;

output means coupled between the first and second means and the output terminals for applying a blended signal to the output terminals, the blended signal consisting of successive intervals of the cutting signal and coagulating signal to alternately produce cutting and coagulation when applied to the body of a patient; and

level control means coupled to the output means for providing an independent adjustment of the amplitude level of the cutting and coagulating components of the blended signal.