US3717152A

US3717152A - Cardiac pacemaker

Info

Publication number: US3717152A
Application number: US00132577A
Authority: US
Inventors: Den Berg J Van
Original assignee: Vitatron NV
Current assignee: Vitatron NV
Priority date: 1967-11-16
Filing date: 1971-04-08
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20
Also published as: NL152761B; NL6715556A

Abstract

A heart stimulator comprises a built-in resonant circuit and an associated rectifier. By means of an oscillator outside the body of the patient, oscillations with a proper frequency may be induced in the resonant circuit, so that the rectifier produces a d.c. voltage. This d.c. voltage is used to reduce the available operating voltage for the final stage of the heart stimulator in order that the safety margin may be checked.

Description

United States Patent [1 1 Van Den Berg [451 Feb. 20, 1973 [54] CARDIAC PACEMAKER [56] References Cited [75] Inventor: Janwillem Van Den Berg, Gronin- UNITED STATES PATENTS gen, Netherlands 3,426,748 2/1969 Bowers ..l28/4l9 P [73] Assignee: Vitatron N.V., Dieren, Netherlands [22] Filed: April 1971 FOREIGN PATENTS OR APPLICATIONS pp NOJ 132,577 985,797 3/1965 Great Britain ..l28/4l9 P Relaed Appficafion Data Primary ExaminerWilliam E. Kamm AttorneyMartin Kirkpatrick [63] Continuation of Ser. No. 773,439, Nov. 5, 1968, abandoned. 7] [30] Foreign A li ti P i it D t A heart stimulator comprises a built-in resonant circuit and an associated rectifier. By means of an oscil- NOV. 16, I967 Netherlands ..67l5556 later outside the y of the patient, oscillations with a proper frequency may be induced in the resonant [52] U.S. CI. ..128/4l9 P, 128/422 circuit so that the rectifier produces a voltage [51] IIIL Cl. ..A61Il 1/36 This voltage is used to reduce tha available [58] new of Search "128/419 419 419 419 operating voltage for the final stage of the heart stimu- 128/421 422 later in order that the safety margin may be checked.

8 Claims, 1 Drawing Figure R1 R7 i g/ L c3 T04 c1 NA 1 n w D1 R6 Tl (:2 A; ll R4 RB KT3 R5 L a CARDIAC PACEMAKER RELATED APPLICATION This case is a continuation of application of Ser. No. 773,439, filed Nov. 5, i968 and now abandoned.

BACKGROUND OF THE INVENTION A heart stimulator is a source of electric impulses which is implanted by a surgical operation in the body of a patient in order to stimulate the heart function.

The conventional heart stimulators comprise an impulse generator such as a multivibrator and a final or power amplifier transmitting the generated impulses to a ventricular heart electrode. Additional circuits may be provided to synchronize the impulse generator with the heart beat and to suppress the impulses during certain critical intervals of the heart beat period. The heart stimulator is entirely transistorized and is energized by a built-in battery.

A certain minimum amplitude of the impulses delivered by the final stage of the heart stimulator is required in order that the heart function may be properly stimulated. This minimum amplitude will be indicated hereinafter as the stimulation threshold. Of course, a certain safety margin is desirable, so that the actual amplitude of the impulses must exceed the stimulation threshold.

The safety margin may be readily checked during the implanting operation. However, the stimulation threshold may change after the implantation of the heart stimulator, for instance if the heart electrode is displaced or surrounded by connective tissue. In such a case it is still possible to check whether the heart function of the patient is properly stimulated, but it is no longer possible to check whether the amplitude of the impulses supplied to the heart electrode exceeds the threshold value with such an amount that there is a sufficient safety margin. It is an object of the invention to remove this disadvantage and to provide means for checking the available safety margin at any time.

SUMMARY OF THE INVENTION According to the invention the heart stimulator comprises a resonant circuit tuned to a predetermined frequency, a rectifier connected with said resonant circuit and an output impedance for said rectifier inserted in the output circuit of the final amplifier of the pacemaker with such a polarity that the dc. voltage generated across the output impedance by the rectifier opposes the battery voltage. Thus, the operating voltage available for the final amplifier may be reduced by inducing oscillations having said predetermined frequency in said resonant circuit from the outside.

The available operating voltage for the final stage of the heart stimulator may now be reduced at any desired time to such an extent that the heart is no longer properly stimulated. By means of electrodes arranged on the skin of the patient it is possible to measure the impulse amplitude at which the heart stimulation ceases as well as the impulse amplitude occurring when no outside oscillations are induced. These two measurements provide a relative stimulation threshold which provides information about the available safety margin.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows the circuit diagram of a preferred embodiment of the heart stimulator according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The heart stimulator shown in the drawing comprises a multivibrator serving as an impulse generator. This multivibrator is equipped with an npn transistor T1 and a pnp transistor T2 cooperating with a plurality of resistors R1, R2, R3, R4 and R5 and with a condenser C1. The emitter of transistor T1 is directly connected with a conductor Al leading to the negative pole of a battery. The collector of transistor T1 is connected through resistor R1 with a conductor A2 leading to a source of reference potential, such as the positive pole of the battery; in addition the collector of transistor T1 is connected through condenser Cl with the base of transistor T2. The emitter of transistor T2 is directly connected with conductor A2, while the collector is connected with conductor Al through a series circuit including resistors R4 and RS. In addition the collector of transistor T2 is connected with the base of transistor T1 through resistor R2. The base of transistor T2 is connected with conductor A1 through resistor R3.

The operation of the multivibrator is as follows. When transistor T2 is rendered conductive its collector voltage increases to such a value that transistor T1 is likewise rendered conductive through resistor R2. The collector of transistor T1 is then substantially at the potential of conductor A1. Condenser C1 is now charged through the diode constituted by the emitter and the base of transistor T2 until the voltage across condenser Cl is substantially equal to the battery voltage. As soon as this condition has been reached transistor T2 is cut off, whereby transistor T1 is likewise cut off through resistor R2. The collector potential of transistor T1 is now increased to a value substantially equal to the potential of conductor A2, whereby the base potential of transistor T2 is increased to about twice this value. Condenser C1 is now discharged through resistor R3; as soon as the voltage across condenser Cl has sufficiently decreased transistor T2 is again rendered conductive and the above described operation is repeated. The time constant of the circuit formed by condenser C1 and resistor R3 is relatively large, for instance of the order of one second, whereas condenser C1 is relatively quickly charged through the emitter-base-path of transistor T2, so that the multivibrator generates short impulses with relatively long intervals between them.

The impulses or pulses generated by the multivibrator occur across resistor R5, so that they are supplied to the final amplifier stage which comprises an npn transistor T3 and two series connected resistors R6 and R7. The output impulses of transistor T3 are supplied through a condenser C2 to a conductor A3 leading to g the ventricular heart electrode. A conductor A4 connected with conductor A1 leads to an indifferent electrode which may consist, for instance, of a conductive surface on the outside of the casing of the heart stimulator.

The emitter of transistor T3 is directly connected with conductor All, while the collector is connected with conductor A2 through the series connected resistors R6 and R7 and with conductor A3 through condenser C2. The base of transistor T3 is connected with the junction of resistors R4 and R5. Transistor T3 is normally cut off and is rendered conductive by each impulse occurring across resistor R5. Thus, transistor T3 operates as a switch. The circuit as described has the advantage that the battery is only loaded during the occurrence of an impulse, so that it has a long life.

According to the invention the heart stimulator com prises a resonant circuit consisting of an inductance L and a condenser C3 connected in parallel with the inductance. This resonant circuit means is connected with a diode D1 of which the output impedance includes resistor R7 and a condenser C4 in parallel with resistor R7. The polarity of diode D1 has been selected in such manner that the dc. voltage generated across resistor R7 by the diode current is opposed to the bat tery voltage.

By means of an oscillator of which the frequency is equal to the tuning frequency of the circuit L, C3 and which is arranged outside the body of the patient oscillations may be induced in the resonant circuit. These oscillations are rectified by diode D1, so that a dc. voltage reducing the operating voltage of transistor T3 occurs across resistor R7. The amplitude of the impulses supplied to conductor A3 is thereby reduced.

By adjusting the power of the oscillator the dc. voltage across resistor R7 may be varied within wide limits. Thus, the dc voltage across resistor R7 may be increased to such an extent that the heart of the patient is no longer stimulated. The impulse amplitude at which the stimulation ceases is measured by means of electrodes arranged on the skin of the patient; the impulse amplitude during normal operation, i.e., without use of the oscillator is measured in the same manner. The ratio of the values obtained by these measurements is the relative stimulation threshold which may be considered as an indication of the available safety margin.

The frequency of the oscillations induced in the resonant circuit must be selected in such manner that they have no influence on the heart functions. The frequency may, for instance, be of the order of 2500 cycles per second.

Although the invention has been described hereinbefore with reference to a specific embodiment the invention is not restricted to this embodiment which may be modified in several ways within the scope of the appended claims; in particular the heart stimulator may contain additional circuits for synchronizing and suppressing the impulses as indicated hereinbefore.

I claim:

1. A heart stimulator adapted to be incorporated in a human body, comprising a battery, a plurality of transistors supplied by said battery, an impulse generator, including at least one of the said transistors, output means including another one of the said transistors, an input for said output means, means for supplying the output impulses of said impulse generator to the input of said output means, a resistor inserted between the collector of the transistor of said output means and one of the poles of said battery, a direct connection between the emitter of the transistor of said output means and the other pole of said battery, 21 pair of output terminals respectively connected with the collector and with the emitter of the transistor of said output means, a resonant circuit tuned to a predetermined frequency, rectifier means connected with said resonant circuit, and an output impedance for said rectifier means inserted in series with said resistor, said rectifier means being connected to said output impedance for generating a DC voltage thereacross, opposing the battery voltage, so that the operating voltage available for said output means is reduced by inducing oscillation in said resonant circuit at said collector from the outside.

2. A heart stimulator adapted to be incorporated in a human body, comprising a battery, an impulse generator, including a first transistor, having its emitter directly connected with a first pole of said battery, a first resistor inserted between the collector of said first transistor and the second pole of said battery, a second transistor having a conductivity type opposite to that of said first transistor, said second transistor having its emitter directly connected with said second pole, a second resistor inserted between the base of said first transistor and the collector of said second transistor, a third resistor inserted between the base of said second transistor and said first pole, a first condenser inserted between the base of said second transistor and the collector of said first transistor, fourth and fifth resistors connected in series between the collector of said second transistor and said first pole, an output means having input and output circuits, means for supplying impulses appearing at the junction between said fourth and fifth resistors to the input circuit of said output means, a pair of output terminals included in the output circuit of said output means, a resonant circuit, said resonant circuit being tuned to a predetermined frequency, rectifier means connected with said resonant circuit and an output impedance for said rectifier means, said output impedance being series connected with said battery in the collector circuit of said output means, said rectifier means being connected to said output impedance for generating a DC voltage thereacross opposing the battery voltage so that the operating voltage available for said output means may be reduced by inducing the oscillations in said resonant circuit from the outside.

3. A heart stimulator as claimed in claim 2 wherein said output means comprises a third transistor having the same conductivity type as said first transistor, having its emitter directly connected with said first pole and having its base connected with said junction, and sixth and seventh resistors connected in series between the collector of said third transistor and said second pole, said seventh resistor being included in said output impedance.

4. A heart stimulator as claimed in claim 3 further comprising a second condenser inserted between the collector of said third transistor and said conductor adapted to be connected with a ventricular heart electrode.

5. A heart stimulator as claimed in claim 3 wherein said resonant circuit comprises an inductance and a thirdcondenser in parallel with said inductance, and wherein said rectifier is inserted between one end of said resonant circuit and one end of said seventh resistor, the other ends of said resonant circuit and said seventh resistor being directly interconnected.

6. A heart stimulator as claimed in claim 3 wherein said output impedance further comprises a fourth condenser in parallel with said seventh resistor.

7. In a heart stimulator adapted to be implanted in a living body and deliver stimulating pulses to the heart thereof, said stimulator including an output stage with a transistor and a first impedance connected in the collector circuit of said transistor, that improvement which consists of DC voltage generating circuitry including inductive means for receiving energy from a source external to said body, a first capacitor connected across said inductive means to form a resonant circuit therewith, a rectifier and a second capacitor connected in series across said resonant circuit, and a second impedance connected across said second capacitor and series connected with said first impedance in the collector circuit of said transistor, said circuitry generating DC voltage across said second impedance in response to said external source, thereby modifying the DC'operating voltage for said output stage and the amplitude of said stimulating pulses.

8. Apparatus as claimed in claim 7, including a battery connected to provide power for the collector circuit of said output stage, said DC voltage generating circuitry being connected with polarity opposing said battery.

Claims

1. A heart stimulator adapted to be incorporated in a human body, comprising a battery, a plurality of transistors supplied by said battery, an impulse generator, including at least one of the said transistors, output means including another one of the said transistors, an input for said output means, means for supplying the output impulses of said impulse generator to the input of said output means, a resistor inserted between the collector of the transistor of said output means and one of the poles of said battery, a direct connection between the emitter of the transistor of said output means and the other pole of said battery, a pair of output terminals respectively connected with the collector and with the emitter of the transistor of said output means, a resonant circuit tuned to a predetermined frequency, rectifier means connected with said resonant circuit, and an output impedance for said rectifier means inserted in series with said resistor, said rectifier means being connected to said output impedance for generating a DC voltage thereacross, opposing the battery voltage, so that the operating voltage available for said output means is reduced by inducing oscillation in said resonant circuit at said collector from the outside.

5. A heart stimulator as claimed in claim 3 wherein said resonant circuit comprises an inductance and a third condenser in parallel with said inductance, and wherein said rectifier is inserted between one end of said resonant circuit and one end of said seventh resistor, the other ends of said resonant circuit and said seventh resistor being directly interconnected.

7. In a heart stimulator adapted to be implanted in a living body and deliver stimulating pulses to the heart thereof, said stimulator including an output stage with a transistor and a first impedance connected in the collector circuit of said transistor, that improvement which consists of DC voltage generating circuitry including inductive means for receiving energy from a source external to said body, a first capacitor connected across said inductive means to form a resonant circuit therewith, a rectifier and a second capacitor connected in series across said resonant circuit, and a second impedance connected across said second capacitor and series connected with said first impedance in the collector circuit of said transistor, said circuitry generating DC voltage across said second impedance in response to said external source, thereby modifying the DC operating voltage for said output stage and the amplitude of said stimulating pulses.