JPH0451176B2 - - Google Patents

Description

TECHNICAL FIELD This invention relates to electrosurgical generators, and more particularly to a generator including means for controlling its output level. The invention further relates to the use of such generators with dipole forceps or handpieces.

Bipolar electrosurgery refers to the use of a handpiece with two small electrodes that produce an electrosurgical current, instead of a single small active electrode and large return electrode as used in monopole electrosurgery. Regarding use.

Background Art The advantages of dipole electrosurgery over monopole electrosurgery are as follows. (1) the use of relatively low power levels, which directly leads to the destruction of less tissue; and (2) the only tissue that is destroyed is that located between the electrodes of the dipole, resulting in the risk of burns at alternating sites. (3) The applied voltage can be made very low. Therefore, to prevent tissue burns and scarring due to sparks at the electrodes.

Bipolar electrosurgery is widely used in surgical procedures on the eye and brain where delicate tissues can be easily destroyed by excessive heat or sparks.

To try to improve the effectiveness of dipole electrosurgery,
Studies have been conducted on changes in tissue impedance during dehydration. As a result, it was found that there were two dehydration phases. The first phase occurs immediately upon application of electrosurgical current. Tissue temperature increases, cell walls are destroyed, and tissue impedance exhibits a decrease. The temperature continues to rise and the moisture is lost as steam. As the tissue dries,
resistance increases. The output voltage rises slightly with increasing resistance, at which point sparks, excessive temperature rise of the forceps, or sticking of the forceps to tissue occurs.

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide an improved electrosurgical generator whose power decreases rapidly with increasing impedance so that the power decays towards the end of the dehydration phase. .

Another object of the present invention is to provide an improved generator of the above type in which the power decreases as the inverse of the square of the tissue impedance.

Another object of the invention is to provide an improved generator of the above type for use in dipole electrosurgery.

It is also a primary object of the present invention to provide an improved electrosurgical generator whose power decreases rapidly with increasing impedance so that the power decays towards the end of the dehydration phase.

Another object is to provide an improved generator of the above type in which one of two different operating modes can be selected for impedances higher than a predetermined value.

Another object of the invention is to provide a generator of the above type in which one of the selected modes provides a constant voltage characteristic and in the other of said characteristics the power is reduced by the square of the impedance of the load. .

Another object of the invention is to provide a generator of the above type which includes a circuit for calculating the required power for different load impedance ranges and matching the actual output to this calculated required power.

Other objects and advantages of the invention will become apparent from the following description and appended claims when considered in conjunction with the drawings.

U.S. Patent No. 3946487, U.S. Patent No. 3980085, U.S. Patent No.
No. 4,188,927 and No. 4,092,986 disclose devices that reduce the output current as the impedance of the load increases. In particular, these U.S. patents
This teaches the use of a constant voltage output where the current decreases as the impedance of the load increases. However, these US patents do not disclose that the output changes with the reciprocal of the square of the impedance of the load. Generally, there is no disclosure in which the output power is reduced at a substantially greater rate than that resulting in constant voltage output in the above-mentioned US patent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Similar parts will be described with reference to the drawings bearing the same reference numbers.

In FIG. 1, an exemplary electrosurgical generator according to the present invention includes a regulated switching power supply 10, an unregulated DC voltage source 11, a radio frequency (RF) generator 12, a voltage and current sensor 14, and a microelectrosurgical generator. It includes a processor controller 16, a nominal power indicator 18, and a foot switch 20. Electrosurgical current is
From said generator is provided a forceps 22 , which is schematically shown in contact with a patient 24 .

The power applied to the load is DC power supply 10
is a function of the voltage from and the impedance of the load. As will be described in more detail below, the sensor 14 produces a detection signal that is proportional to the load voltage and current applied to the controller 16 on lines 15 and 17, respectively. This control device is
The sensed signal is quantified to calculate the impedance of the load and the actual power delivered to the load.

The required load power, which is a function of the calculated load impedance and the nominal power selected by the operator at 18, is also calculated. A graph of the required load power for a nominal power of 50 watts is shown in FIG.

At low load impedances, typically less than 70Ω, the calculated power requirements are reduced to prevent tissue destruction or overheating of the radio frequency output. In particular, the control voltage provided on line 19 to power supply 10 controls the output power to maintain constant load current within this low value impedance range. Within an intermediate range ranging from approximately 70 to 100 ohms, the calculated power requirement is held constant at the selected nominal power.

For impedances greater than 100Ω, the operator can select one of two operating modes. As shown in FIG. 2, the calculated power requirement is reduced at the beginning of these modes while keeping the voltage constant, but this effect is similar to that of known generators.
In the second mode, the calculated power requirement is reduced at a substantially greater rate than would occur when the voltage was held constant. Preferably, the calculated power requirement is reduced by the square of the load impedance in the second mode.
Thus, for example, the calculated power requirement for a certain load with an impedance of 200Ω is
This is one quarter of what is needed for a 100Ω load impedance. For example, if the impedance is increased to about 800 Ω in the second mode of operation, a constant voltage characteristic can be configured, since at this level the level of power may be impractically small.

After the requested power is calculated for a range of nominal power and load impedance, the control voltage applied to line 19 is adjusted by the appropriate amount to match the actual power to the requested power. , a comparison is effectively made between the requested power and the actual power.

Due to differences in the amount of tissue contact, tissue heating, etc., the impedance of the load changes continuously during the electrosurgical procedure. Therefore, the microprocessor controller 16 will operate as long as the foot switch 20 or dipole hand switch (not shown) is closed.
The measurement, calculation and correction process is repeated approximately every 20 milliseconds.

Next, the microprocessor is one of the 8048 series of single-chip microprocessors.
Please refer to FIG. 3, which is a general flow chart of a program executed by the microprocessor controller 16, which may be an INTEL 8039 and the program may be stored in an INTEL 2716 type programmable memory. After an initialization routine (not shown), program control is passed to routine COLDST26 (cold start), which calculates certain parameters and starts certain functions. The program first calculates I _nax , the current value that would occur at 70Ω for some nominal power selected by the operator. For example, if the operator selects a nominal power of 70 watts, the current delivered into a 70 ohm load will be 1 amp, so the value of _Inax will be 1 amp in this case. The range of nominal power available to the operator generally ranges from 0 to 70 watts. The nominal power selected by the operator is P _nax
, and occurs in the intermediate range of impedances ranging from 70 to 100 ohms. Maximum power is 70~
Since it occurs over a range of 100Ω, and the largest current that occurs within this range occurs at 70Ω, I _nax is calculated at 70Ω as described above. in general,
I _nax = (P _nax /70) ^1/2 , where P _nax is equal to the nominal power selected by the operator and 70 is
corresponding to a 70Ω load).

COLDST also calculates the initial parameter V _nax as follows. The operator shall select a nominal power of 25 watts. The resulting voltage of a 100Ω load for this power value corresponds to the value V _nax ,
Therefore, in this case, V _nax is 60 volts.
As mentioned above, P _nax occurs over a range of 70 to 100 ohms. Additionally, maximum power occurs at a 100Ω load. Therefore, V _nax is calculated as follows. In general, V _nax = (100P _nax ) ^1/2 = 10(P _nax ) ^1/2 After calculation of V _nax and I _nax , COLDST is a small control voltage on line 19 to power supply 10.
Add AFB and turn on RF generator 12.
COLDST then waits approximately 0.01 seconds to allow the RF output to stabilize before passing control to control routines GETP 28 and CNTLP 30.
GETPWR is the load voltage signal present on line 15
Detecting V _SEN and the load current signal I _seo occurring on line 17. Load power P _LOAD is calculated as V _SEN I _SEN . Furthermore, the load impedance Z _LOAD is V _SEN /
Calculated as I _SEN . A determination is also made about the impedance range over which the impedance of the load occurs. Thus, a first impedance range flag (not shown) is set if the load impedance range is less than 70Ω, and a second flag is set if the load impedance range is between 70 and 100Ω. , 100Ω or more, the third flag is set. It will be appreciated that a considerable amount of tolerance is provided in the selection of the impedance range, which can span, for example, from 60 to 115 ohms.

As mentioned above, in the high impedance range the operator can select one of two different modes. Depending on the selected mode, further flags are set by COLDST to indicate the selected mode. routine
CNTLP examines the above flags to determine which algorithm below should be executed.
These algorithms are as shown in Figure 3.
LOZ32, MIDZ36, ZOL38 and HIZR2
It is 40. All of these algorithms ultimately transfer control to routine AFBADJ34.
These routines will be discussed individually next.

Assuming the load impedance is measured as 40Ω, CNTLP sends control to LOZ32. A correction factor is calculated which will constitute the constant current characteristic described above for the low impedance range. In particular, if I _SEN = 1.2 amps and I _nax = 1 amp, then the correction factor is
Calculated as I _nax /I _SEN . Therefore, the calculated factor is equal to 1.0/1.2. After calculating the correction factor, control is passed to AFBADJ 34, which increases or decreases the control voltage AFB based on the calculated correction factor.
Therefore, if the value of AFB is 10 volts,
This will be reduced by a correction factor of 1.0/1.2. In this way, the current remains constant at the value I _nax (1.0 amps) over the low impedance range. In this example, the value I _SEN is the value I _nax
I would like to draw your attention to the fact that it exceeds the above. Regardless of whether I _SEN exceeds I _nax , the correction factor is set to I _nax / over the entire lower impedance range by the LOZ routine.
Calculated as I _SEN .

After the corrected control voltage is applied to power supply 10 via line 19, a test is performed to determine whether the operator can still operate the generator to provide electrosurgical power to the forceps. This test is performed at 42. If the generator is energized for this purpose, control is returned to GETPWR. Execution of the GETPWR to AFBADJ routine takes approximately 20 milliseconds in most cases, so the power delivered to the load is constantly being adjusted according to the detected load conditions. If there are no more energization conditions, the routine returns to the initialization mode where the output is shut off and some self-test routine is performed while waiting for the next energization condition. This characteristic is not shown in the flow chart of FIG.

As mentioned above, tissue impedance tends to increase as the dry state progresses. Therefore, assume that the next load measured by the GETPWR routine is 80Ω. The MIDZ flag is set, the load power is calculated, and routine CNTLP again determines the energized flag and passes control to the MIDZ routine 36. Here, the correction factor is calculated according to the formula (P _nax /P _LOAD ) ^1/2 . where P _nax is equal to the nominal power selected by the operator, and P _LOAD =V _SEN I _SEN as calculated in GETPWR. Therefore, if the actual load power P _LOAD is 60 watts and the nominal power
If P _nax is 70 watts, the calculated correction factor is (7/6) ^1/2 . Once this correction factor is determined, control is passed to the AFBADJ routine 34 where the correction factor is multiplied by the previous value of the control voltage AFB applied to line 19. Adjustment of the control voltage and addition to line 19 is
It is performed in the same manner as previously described for the LOZ routine.

As more time passes, the impedance continues to increase. Therefore, assuming the drying mode is still acceptable to the operator, the control
Returned for GETPWR and CNTLP. Furthermore, assuming that the operator selects mode 1 for a high range of impedances, CNTLP
30 turns the control to ZOL after detecting a suitable flag.
It will be moved to 38. If the impedance calculated by GETPWR is now 200Ω, the power applied to it will have a constant voltage characteristic as described above with respect to FIG. In particular, the constant voltage will be V _nax as calculated by the COLDST routine. To configure this constant voltage characteristic, ZOL calculates a correction factor determined by the formula V _nax /V _SEN . However, V _SEN
is equal to the load voltage sensed by GETPWR. If the detected voltage is 70 volts and V _nax
If is 50 volts, the correction factor is 5/7.
AFBADJ uses this correction factor in the same way as described previously for LOZ and MIDZ to
Adjust the control voltage given to 9.

If the operator selects mode 2,
This condition, along with the fact that the impedance is now in the high impedance range,
It will be detected by CNTLP. P _nax
Assume that the impedance at this time is 200 Ω while the current is 50 watts and P _LOAD = 60 watts.
The correction factor is the impedance when P _nax is Z _nax
(As shown in FIG. 2, when Z _nax =100Ω), it is calculated as (Z ² _nax ·P _nax /Z ² _LOAD ·P _LOAD ) ^1/2 ). Therefore, in the above case, this factor is (10000×50/40000×60) ^1/2 = (5/24) ^1/2
be equivalent to. Again, after computation of corrections, the control is
Sent to AFBADJ to adjust the control voltage on line 19. Attached by reference to the specification is a program list for the flow chart of FIG. 3, which also includes various initialization, test and error programs.

Next, FIGS. 4a and 4b, which are schematic diagrams of the switching power supply 10, high frequency generator 12, and current sensor 14 shown in FIG. 1, will be described.
The switching power supply includes a standard switching power supply circuit 44 manufactured by Silicon General. The remaining integrated circuits of the invention are also manufactured by Silicon General
and other such companies' products. The switching power supply is of conventionally well known form and includes a switching transistor 46 and an inductor 47;
and an output line 48 that provides a regulated high voltage to the output transistor 52 of the generator 12.
Contains. The supply voltage applied to line 48 is obtained from terminal 50 and is typically about 100 volts. terminal 50
The voltage at switching transistor 4
6, an inductor 47 and a capacitor 49, in particular the longer the cut-off time of transistor 46, the smaller the magnitude of the DC voltage applied to line 48. line 4
The voltage DC SENSE proportional to the voltage at resistor 5
4,56 to terminal 2 of circuit 44. This voltage is compared to and follows AFB on line 19.

ON/OFF from circuit 44 to switching transistor 46 via transistors 58 and 60
An OFF pulse is given. The repetition rate of these pulses is determined by resistor 62 and capacitor 64 connected to R _T and C _T of circuit 44. The width of these pulses, and thus the ON/OFF time of transistor 46, is a function of the difference between AFB and DCSENSE. Therefore, as the impedance changes in the dehydration procedure,
Power supply voltage follows AFB.

Output power is delivered to the load via lines 66 and 68, which are further connected to an output transformer 70. Generator 12 is energized by a 750 KHz signal applied to terminal 72, where the signal is amplified and applied to output transistor 52, which in turn connects primary winding 74 of transformer 70. energize.

Load current is sensed at transformer 76 and 78
is converted into a voltage representing a current by a conversion circuit shown in . This voltage is applied to the microprocessor 16
is applied on line 17 as a signal I _SEN . Additionally, a voltage representative of the load voltage is applied to winding 8 of transformer 70.
Obtained from 0. This signal is transmitted to the signal conversion circuit 82
The load voltage V _SEN on line 19 is converted by
occurs.

The values given for resistance are in ohms and the values for capacitance are in microfarads, unless otherwise specified, and these values are exemplary of embodiments of the invention.

The overall operation of the invention is such that a very small heat sink is required for heat dissipation, so a 3-4 watt sink connected to transistor 52 is suitable; Such a sink would involve very small values. This is due to the fact that the amplifier is substantially matched to a load of 100 ohms, and a very limited impedance range around this value is the maximum value provided for the load.

Substantially reducing the load impedance from 100 ohms will cause the power to drop as described above and shown in FIG. 2. There is no need for the amplifier to generate substantial power at a reduced impedance from the matched impedance. Therefore,
Even at impedances removed from 100 ohms, only a small amount of power is involved, which makes the small heat sink described above adequate for such relatively small powers.

It is to be understood that the above detailed description of embodiments of the invention is merely exemplary. Thus, for example, the principles described above are also applicable to monopole electrosurgery. Various changes may be made in construction and construction details without departing from the spirit and scope of the invention as set forth in the following claims.

[Brief explanation of the drawing]

1 is a block diagram illustrating an exemplary electrosurgical generator according to the present invention; FIG. 2 is a graph illustrating different modes of operation of the generator of the present invention; FIG. Flow chart showing the program executed and stored therein, and Figures 4a and 4b
1 is a schematic diagram of the switching power supply, generator, and voltage and current detection circuit of FIG. 1; 10...DC power supply, 11...DC voltage source, 12...
High frequency generator, 14... Voltage and current sensor, 15, 17, 19... Line, 16... Microprocessor controller, 18... Nominal power indicator, 20... Foot switch, 22... Forceps, 24...
Patient, 44... Switching power supply circuit, 46... Switching transistor, 47... Inductor, 48...
Output line, 49... Capacitor, 50... Terminal, 52... Output transistor, 54, 56, 62
...Resistor, 58,60...Transistor, 64...Capacitor, 66,68...Line, 70...Output transformer, 72...Terminal, 74...Primary winding, 76
...Transformer, 78...Conversion circuit, 80...Winding, 82...
Signal conversion circuit.

Claims (1)

Claims: 1. An electrosurgical energy source, an apparatus for connecting the source to a load including a patient, and a control apparatus for regulating the actual power provided from the source to the load; an electrosurgical generator comprising: a device for determining the impedance of the load;
A correction factor calculation device for calculating a correction factor corresponding to required load power, wherein the correction factor is such that the power supplied to the load is proportional to the reciprocal of the square of the impedance of the load. and a device for adjusting the source so that the actual power follows the required load power in response to the correction factor. Electrosurgical generator. 2. The generator of claim 1, wherein said controller includes a microprocessor for regulating the actual power delivered from said source to said load. 3. Generator according to claim 1, characterized in that a device is provided for selecting the nominal power supplied to the load, the correction factor being also dependent on the nominal power to calculate this correction factor. . 4. The generator of claim 3, wherein said nominal power varies between 0 and 70 watts. 5. The generator of claim 1, further comprising a heat sink for said electrosurgical energy source, said heat sink having a capacity of not more than about 4 watts. 6. For all load impedances below a second predetermined value that is less than the predetermined value, the correction factor calculation device sets a second value such that the current flowing through the load remains substantially constant.
A generator according to claim 1, characterized in that the generator calculates a correction factor for . 7. A device is provided for selecting a nominal power to be supplied to the load, and the second correction factor is
be equal to I _nax /I _SEN , where I _nax is the current flowing through said second predetermined value impedance with said nominal power applied and I _SEN is the actual current flowing through said load. 7. A generator according to claim 6, characterized in that: 8. The generator of claim 6, wherein the second predetermined value is approximately 70Ω. 9. For all load impedances between the predetermined value and a second predetermined value smaller than the predetermined value, the correction factor calculation device maintains a state in which the power supplied to the load is substantially constant. 2. A generator as claimed in claim 1, characterized in that the third correction factor is calculated in such a way that: 10 A device is provided for selecting the nominal power to be supplied to the load, and the third correction factor is (P _nax /P _LOAD ) ^1/2 (where P _nax is the nominal power and P _LOAD is the nominal power to be supplied to the load). 10. A generator as claimed in claim 9, characterized in that it is equal to the actual power supplied to the generator. 11. The generator of claim 9, wherein the predetermined value and the second predetermined value are approximately 100 and 70 ohms, respectively. 12. For all load impedances greater than the predetermined value, the correction factor calculation device calculates a fourth correction factor such that the voltage across the load remains substantially constant. A generator according to claim 1, characterized in that: 13. A device is provided for selecting a nominal power to be supplied to the load, and the fourth correction factor is
V _nax /V _SEN (where V _nax is the voltage across the impedance of the predetermined value with the nominal power applied and V _SEN is the actual voltage across the load) 13. The generator of claim 12. 14. The generator according to claim 12, wherein the predetermined value is about 100Ω. 15 A device is provided for selecting the nominal power to be supplied to the load, and the correction factor is [10000P _nax / (Z _LOAD ² ) P _LOAD ] ^1/2 (where P _nax is the nominal power and Z _LOAD is 2. A generator as claimed in claim 1, characterized in that the impedance of the load and _PLOAD are equal to the actual power delivered to the load. 16. The generator according to claim 15, wherein the predetermined value is about 100Ω.