JP3529837B2 - Medical device current sensor with continuous monitor - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the loading end of other electrical conductors including, but not limited to, electrical cables or electrosurgical trocars and radiofrequency ablation devices. More specifically, the present invention relates to medical systems and instruments that handle current delivered to parts, and more particularly to current sensing devices that determine the amount of current delivered.

[0002]

BACKGROUND OF THE INVENTION It is often necessary to determine the amount of current delivered to the end of an electrical conductor, such as a cable. For example,
U.S. Patent Application No. 08 / 009,598, "Current Sensors for Medical Devices Including Connector Cables", Application 1993 1
No. 07 / 901,024, "Electrosurgical Radial Needle Assembly with Bipolar Electrodes," 27th March,
Filed June 19, 1992, US Patent Application No. 07/85
No. 3,149, "Electrosurgical Spiral Needle Assembly", 1
The contents of the application filed on March 17, 992, all of which are related applications of this application in the United States, are incorporated herein to disclose an electrosurgical needle assembly. And, in this, the tongue needle comprises an electrosurgical cutting element connected to the electrosurgical generator by a cable. And in one preferred embodiment, it is desirable to inhibit the electrosurgical generator as the tip of the tongue needle penetrates through the wall of the body cavity, including, for example, the peritoneum.

As disclosed in these applications, this delivered current changes when penetration is achieved,
This can be done by sensing the current delivered by the electrosurgical generator. Also, another preferred example is for radio frequency (rf) ablation procedures that require tightly controlled delivery of electrosurgical currents. It should be understood that the invention is applicable to situations where it is necessary to know the amount of alternating current delivered to a load at the end of an electrical conductor, such as a cable, but the invention does not It is described below with particular reference to a surgical needle device.

Considering the problem to be solved in more detail, the total current produced by the generator is high when the delivered current is high frequency and high voltage, such as the current output produced by the electrosurgical generator. Does not really show the actual current delivered to the end of the electrical connecting cable. This
The mismatch or error in is due to the distributed capacitance on the current return of the generator. Current flows along the length of the cable, the amount of current being determined by voltage, frequency, distributed capacitance to ground (or return) and cable length.

Thus, as shown in FIG. 10, the electrosurgical generator is designated G and the load impedance (eg, the impedance of the tissue operated on by the electrosurgical electrode or ablation element) is designated Z _L. The shunt impedance, or "leakage" capacitance, which represents the distributed capacitance to ground, is designated _Zca . If the voltage of the generator is V, the total current I _t is given by the formula I _t = V / Z _ca + V / Z _L
Represented by The current delivered to the load is V and I
_Although often obtained by measuring _t and reducing the effect of capacitance, capacitance is often unknown, especially in electrosurgery, and actually changes with cable position in an unpredictable manner, and This makes inaccurate simple current measurements at the cable end generator.

[0006]

SUMMARY OF THE INVENTION In the present invention, the direct measurement of current on the power supply side is inaccurate due to the effects of the distributed capacitance of the connecting cable or other connections between the power supply and the load. In the environment as described above, a current sensing device is provided which allows an accurate measurement of the current actually delivered from the medical instrument's power supply to the load.

In a preferred embodiment of the present invention, the alternating current delivered from the power supply to the load formed in the medical device connected to the end of the main electrical conductor for supplying current to the medical device from the power supply. A current sensing device is provided for sensing. In the device, the distributed capacitance between the main electrical conductor and the return path to the power supply prevents accurate measurement of the current delivered to the medical device load from measuring the current at the power end of the main electrical conductor. Then, the current sensing device is an array in the vicinity of the main electrical conductor in the longitudinal direction, such that the current flowing through the reference electrical conductor associated with the inherently distributed capacitance, the reference electrical conduction from the load A current delivered to the medical device load that offsets the effect of the distributed capacitance with the reference electrical conductor connected to the medical device load via the amount of load impedance that effectively insulates the body. performing current measurements corresponding to the current flowing through the reference electrical conductor comprises a subtracting means for subtracting from the total load current flowing through the medical device.

The current sensing device further includes the reference voltage.
The air conductor preferably comprises detection means for sensing whether it is intact. In a preferred embodiment, the impedance value is a known value and the detection means comprises an impedance measuring device for sensing the current flowing through the reference electrical conductor. Advantageously, said impedance measuring device comprises a circuit connected between a main electrical conductor and a reference electrical conductor, comprises a fixed voltage source and comprises a current measuring device connected in series with the fixed voltage source. Is.

[0009] To insulate the induction direct current from the power source to deliver an alternating current, a plurality of capacitors are the main and reference potential
It is preferably connected in series with the air conductor. The subtraction means preferably comprises a magnetic subtraction device. A magnetic subtractor is a main electrical conduction member extending through a current transformer in a first direction such that the output of the current transformer is related to the difference in current flowing through the main and reference electrical conductors. It is expedient to have a current transformer having a reference electrical conductor extending through the current transformer in a direction opposite to the body.

Other features and advantages of the invention are set forth or made apparent in the following detailed description of the preferred embodiments of the invention.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a block diagram of one preferred embodiment of a current sensing device or system of the present invention integrated into an electrosurgical trocar assembly is provided. The suture needle assembly is an electrosurgical device or
It includes a generator (ESU) 10 connected to an electrosurgical needle 12 as disclosed in the above-mentioned application using the main electrical conductor 14 of the connecting wiring or cable 16.
ESU 10 includes a pause or cutoff circuit 18, which corresponds to, for example, the one described in the above-mentioned application and also provides a pause for ESU 10. That is, the power supply to the conical needle 12 from the ESU 10 is discontinued or cut off upon penetration of the distal end of the conical tube through the wall of the cavity (eg, abdominal wall) in question. In this embodiment, the current sensing unit 20 is co-located with the ESU 10, although a separate controller or control box is provided.

As mentioned above, an important issue for systems where current sensing is done in the ESU (or in the remote control box) is that at the frequencies involved, the connecting cable 16
Provides a fairly large varying "leaky" impedance that makes it difficult to detect cut-off points. According to the embodiment of FIG. 1 and FIG. 2 and according to FIGS. 3 to 5, the reference wiring or reference electrical conductor 22 is also connected in the cable 16, ie in the vicinity and in close proximity. Wire that carries high-frequency current to the needle 12 (main electrical conductor) 1
4 and provided in parallel, but, the cutting element 12a of the shaking Kanhari 12 is not connected. After all current sensor 20
Is the "hot" (main) wiring or main electrical conductor 14
, And the difference between the load conditions seen by the reference wiring or reference electrical conductor 22 can be detected.

As mentioned above, this array of reference wires 22 is also shown schematically in FIG. FIG. 2 is a schematic circuit diagram similar to FIG. 10, and similar symbols are used. As illustrated, the second electrical conductor or reference electrical conductor 22 is primarily or "hot" closest to the electrical conductor 14, the reference current concatenated current standards return of the generator 10 from the wiring 22 It is arranged to be equivalent to the current coupled from the main electrical conductor 14 to the current return of the generator 10 except at the end of the wiring 22. The preferred technique for accomplishing this is to connect both electrical conductors 14 and 22 to a generator current source and fit the electrical conductors 14 and 22 together.

As explained above, only the main electrical conductor 14 is actually connected at the end to the load (Z _L ) and the second
The electrical conductor is terminated just before the load. Second electricity
The conductor or reference electrical conductor 22 has an impedance Z _cb to ground for leakage capacitance, ie for distributed coupling capacitance. The closer the second electrical conductor 22 is to the end of the main electrical conductor 14, the greater the current loss through capacitive coupling. Because, when both current losses are equal, the total current delivered to the tip is, as described above, from the total current in the main wiring 14 to the second electrical current.
It is determined by subtracting the leakage current in conductor 22. That is, I _ZL = I _i −I _cb . Because I _i and I _cb can be accurately measured at the generator side of cable 16, so if I _cb = I _zca , then
I _ZL can be ascertained by subtracting I _cb from I _i .

Several methods are used to perform the above referenced subtraction. In the embodiment of FIG. 1, this can be done by magnetic subtraction using a current transformer 24 as illustrated in the schematic circuit diagram of FIG. In particular, the main electrical conductor 14 is the current transformer 24.
Arranged in a given direction through the second electric
The conductors or reference electrical conductors 22 penetrate the same current transformer 24 and are arranged in opposite directions as illustrated in FIG. The output of the current transformer 24 is thus the current difference between the main electrical conductor 14 and the second electrical conductor 22, ie the current delivered to the load Z _L (ablation element 12a). This current is the current sensed by the current sensor 20 and is used to control the cutoff circuit 18.

It is noteworthy that if the second electrical conductor 22 is destroyed, the current reading will be inaccurate. For this reason, the present invention also provides a second
The present invention relates to providing a technique for determining whether or not the electric conductor 22 is perfect. In particular, when the operation of ESU10 starts, if the minimum level of current is not sensed in the second electrical conductor or reference electrical conductor 22, to sense the current, device in an electrosurgical generator 10 (Fig. 1 18
And 20), which generates a warning signal and is set to turn off the electrosurgical generator 10. In the magnetic subtraction embodiment of FIGS. 1 and 3, this is done by simply adding a current transformer 26 through which the second electrical conductor 22 passes, as shown in FIG.

Another method of performing the desired current subtraction is illustrated in FIG. FIG. 5 is similar to FIGS. 3 and 4, but in FIGS. 3 and 4 the current transformer 24 is replaced by impedances 28 and 30 connected to the respective main and reference electrical conductors 14 , 22. The differential voltage amplifiers 32 and 34 have respective impedances 28
And 30 are connected from both ends, and the outputs of these two amplifiers are connected to another differential amplifier 36. In this way, the output of the latter becomes the voltage V proportional to the load current. Monitoring the integrity of the reference electrical conductor 22 is
Impedance 30 arranged on the second electrical conductor 22
It can also be achieved in the embodiment of FIG. 5 by adding, for example, an output connection 34a to the output of the differential voltage amplifier 34 so as to measure the voltage itself across

A further approach to the basic problem described above is illustrated with reference to FIG. In this embodiment, FIG.
A current sensor 40 is positioned at the end of the main or "hot" electrical conductor 14 (not referenced electrical conductor), as schematically illustrated in FIG. If no affected by the capacitance output of the sensor 40 to ground, i.e. output (passed through the optical fiber cable) digital signals, light, transmitted radio-frequency signals (r.f.) or current If the DC voltage corresponds to, the load current is accurately sensed. Any of a number of different types of current sensors, including thermal sensors and thermistors (or thermocouples) for converting signals into usable voltages, rectifiers for converting current to DC voltage and current transformers for smoothing, etc. One is used.

Referring to FIG. 7, the next embodiment of the invention is shown. FIG. 7 is similar to FIG. 10 and similar displays are used. FIG. 7 differs from FIG. 10 in the following points. That is, in order to overcome the previously discussed problems, a switch device or switch 42 is provided at the load end of the cable, ie at the end where the load impedance Z _L is included. In operation, the switch 42 is kept open, the load current is brought to a known zero and the generator G (Fig.
(Corresponding to the ESU 10 of the). Assuming minimal movement of the connecting cable (eg the cable corresponding to cable 16) such that the distributed capacitance is constant, the resulting current can be measured and used as a reference level. This reference current level is subtracted from the total generated current when switch 42 is activated (closed).
The current is then delivered to the load (and distributed capacity).
The result of the open circuit switch measurement can also be used to calculate the distributed capacitance, and the result of the calculated value is used to determine the current delivered to the load.

Referring to FIG. 8, a more important embodiment of the invention is shown. Two main and reference electrical conductors 1
When 4 and 22 have been shown with the not connected at the end of the load, i.e., when the reference electrical conductor 22 is shown without being connected to a load to high between the load and the criteria electrical conductor 22 that can essentially occur Hence the same effect by connecting a resistor or other impedance values it will be appreciated from the foregoing description. this is,
This is done in the embodiment of FIG. 8, in which the reference electrical conductor 22 is connected to the load Z _L via a known resistor R1. This known value is then of sufficiently high resistance for the cancellation circuit, yet allows cancellation or monitoring of the reference electrical conductor 22 to ensure that the reference electrical conductor 22 is complete. It is low enough. In this embodiment, capacitors C1 and C2 are also added to the basic circuit illustrated in FIGS. 3 and 4 to isolate the induced direct current from generator 10.

The continuity of the supervisory circuit of FIG. 8 is also different than that of FIG. In the embodiment of FIG. 8, the impedance measuring device or circuit 46 provides a fixed DC voltage .
Form of battery B and current measuring device or ammeter A
It is prepared in the state . It is then connected to the two electrical conductors 14 and 22. The resistor R1 is added to the tip of the device. If the impedance measuring device 46
If one is connected in the circuit and determines that it is the correct value (determined by the ammeter A reading), then both electrical conductors 14 and 22 are considered to be perfect.

With suitable filtering and insulation, the impedance measuring device will also give good results with alternating current. According to a further variation of the illustrated embodiment of FIG. 8, an impedance measuring device 46 is provided so that the second, separated current impedes DC saturation of the current transformer 24.
Can be provided to the current generated by a current transformer 24 of opposite polarity.

Referring to FIG. 9, a particular illustration of the embodiment of FIG. 8 is shown. The circuit of FIG. 9 includes an isolated power supply 48 which includes a transformer T1, a diode D1 in series and a shunt capacitor C3 connected across three series connected resistors R2, R3 and R4. Is included.
The inputs of the pair of operational amplifiers A1 and A2 are resistors R2 and R.
3 and R4 and the reference voltage via the branch connection.
It is connected to the air conductor 22. As illustrated, power supply 4
One side of 8 is connected to the main electric conductor 14 via the resistor R5 and the capacitor C4, and is connected to the reference electric conductor 22 from the junction point of the resistor R5 and the capacitor C4. The output of the operational amplifiers A1 and A2 is one of the power supplies 48 (the resistor
6) and the base of transistor S1. The emitter of the transistor S1 is connected to the other side of the power supply 48. The collector of the transistor S1 is connected in series with the light source LED1. The light source LED1 is connected to one side of the power source 48 via the resistor R7. The light receiving portion of the phototransistor PT1 receives light from the light source LED1. The emitter of the phototransistor PT1 is grounded, and its collector is connected to the power supply terminal (+5
V). The output is supplied from the connection point of the resistor R8 and the collector of the phototransistor PT1.

The overall operation of the embodiment of FIG. 9 is similar to that of FIG. 8 and the operation of current transformer 24 is the same. The non-limiting values used in the exemplary paradigm are shown in FIG. Since the ESU (corresponding to the power supply 10) is already capacitively isolated from its output, the capacitor C in FIG.
Capacitors corresponding to 2 It should be noted that not used in omitted Figure 9.

While this invention has been described with respect to particular exemplary embodiments, without departing from the scope and spirit of this invention,
It will be appreciated by those skilled in the art that changes and modifications can be made in these exemplary embodiments.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a first embodiment of the present invention.

FIG. 2 is a schematic circuit diagram similar to FIG. 10 of the first embodiment of the present invention.

FIG. 3 is a schematic circuit diagram similar to FIG. 2, but including a magnetic subtraction device.

FIG. 4 is a schematic circuit diagram similar to FIG. 3, but including a reference electrical conductor perfect detector.

FIG. 5 is a schematic circuit diagram similar to FIG. 10, of another example of the first embodiment of the present invention.

FIG. 6 is a schematic block diagram of yet another embodiment of the present invention.

FIG. 7 is a schematic circuit diagram similar to FIG. 10 of still another embodiment of the present invention.

FIG. 8 is a schematic circuit diagram similar to FIGS. 3 and 4 of still another embodiment of the present invention.

FIG. 9 is a circuit diagram showing a specific example of the embodiment of FIG.

FIG. 10 is a schematic circuit diagram illustrating the effect of distributed capacity in measuring the current delivered from a generator to a load.

[Explanation of symbols]

10 ... Generator (ESU) 12 ... Tooth tube needle 12a ... Cutting element 14 ... Hot (main) electric conductor (main wiring) 16 ... Cable 18 ... Cut-off circuit 20 ... Current sensor 22 ... Reference electric conductor (reference wiring) ) 24 ... Current transformer 26 ... Current transformer 28 ... Impedance 30 ... Impedance 32 ... Differential voltage amplifier 34 ... Differential voltage amplifier 36 ... Differential amplifier 40 ... Current sensor 42 ... Switch 46 ... Impedance measuring device 48 ... Insulated power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-233780 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 18 / 00-18 / 28

Claims (7)

(57) [Claims] 1. A power supply (10) to a medical device load (12).
The load formed in the connected medical equipment at the distal end of the main electrical conductor (14) for supplying current to, there in a current sensing device for sensing an alternating current is delivered from the collector <br/> source Te, distributed capacitance between the return of the main electrical conductor (14) to said power source, a measurement of the current in the power supply end of the main electrical conductor (14), is delivered to the medical device load in preclude the accurate measurement of the current that the current sensing device, such that the current flowing through the reference electrical conductor (22) is related to essentially the distributed capacitance, before
In the vicinity of the main electrical conductor (14) along its length
Is sequence, and said reference electrical conductor from said load (2
2) it was connected to effectively the medical device load through the load impedance value, such as electrically insulate the <br/> reference electrical conductor (22), the effect of the distributed capacitance to offset the by comprising a subtracting means for subtracting a current flowing from the total load current flowing to the medical device through the reference electrical conductor (22), the delivered current to the medical device load A current sensing device that makes corresponding current measurements. 2. The current sensing device of claim 1, wherein said current sensing device further comprises detection means for sensing whether said reference electrical conductor (22) is intact. 3. The current of claim 2 wherein said impedance value is a known value and said detecting means comprises an impedance measuring device for sensing the flow of current through said reference electrical conductor (22). Sensing device. 4. The impedance measuring device is the main unit.
Electrical conductor (14) and said reference electrical conductor (22)
4. The current sensing device of claim 3, comprising a circuit connected between and including a fixed voltage source, and a current measuring device connected in series to the fixed voltage source. 5. The current sensing device further comprises a capacitor connected in series with the main electrical conductor (14) to isolate a direct current induced from a power supply delivering an alternating current.
5. The current sensing device of claim 4, comprising a capacitor (C1, C4) connected in series with a capacitor (C2) and the reference electrical conductor (22) . 6. The current sensing device of claim 1, wherein said subtracting means comprises a magnetic subtracting device. And wherein said magnetic subtraction device current transformer, the difference between currents the output of the current transformer flows through the main electrical conductor (14) and the reference electric conductivity <br/> conductors (22) As related, the main extending through the current transformer in a first direction.
7. The current sensing device of claim 6, comprising an electrical conductor (14) and the reference electrical conductor (22) extending in opposite directions through the current transformer.