Pulse forming circuits

• US 5,370,664 A
• Filed: 08/10/1993
• Issued: 12/06/1994
• Est. Priority Date: 04/12/1991
• Status: Expired due to Term

• Current Assignee: Creditanstalt-Bankverein (Unicredit SPA)
• Original Assignee: Physio-Control Incorporated (Stryker Corporation)
• Inventors: Yerkovich, Daniel, Morgan, Carlton B., Maier, Donald C.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): GILBERT, SAMUEL G
• Application Number:
  US08/104,441
• Time in Patent Office: 483 Days
• Field of Search: 607/2, 607/4-7, 607/11, 607/68, 607/73, 607/74, 606/32-34, 606/36-40
• US Class Current: 607/6
• CPC Class Codes: A61N 1/3904 External heart defibrillators [EHD]
• CPC Class Codes: A61N 1/3906 characterised by the form of the shockwave
• CPC Class Codes: A61N 1/3912 Output circuitry therefor, e.g. switches
• CPC Class Codes: G01K 1/18 for reducing thermal inertia

Abstract

Circuits for controlling the current flow of an energy pulse as a function of the temperature of a resistive element in the circuit so that the current flow varies over time in accordance with a predetermined waveform. The circuits include at least one negative temperature coefficient thermistor connected between an energy storage device and connectors for delivering energy stored in the storage source to an external load. In one embodiment of the invention the circuit includes a second thermistor for shunting a residual portion of the current delivered by an energy pulse away from the external load. In another embodiment of the circuit, a small inductive device is used for adjusting the shape of the predetermined waveform. In yet another embodiment of the device, a plurality of thermistors arranged in a bridge-like configuration are used to control the current of the energy pulse so that its waveform is biphasic. Heat sinks may be attached to the thermistors for cooling the latter so as to increase the rate at which energy pulses may be delivered by the circuits.

Claims

1. In a medical instrument for delivering an electrical energy pulse to a patient, wherein the medical instrument includes a source of energy, an energy storage means, a pair of electrodes that are attachable to the patient, and connecting means for connecting energy stored in the energy storage means to the pair of electrodes, the improvement comprising a current control means connected in series with the connecting means for varying over time a current waveform that can flow from the energy storage means to the pair of electrodes to produce a current waveform having a magnitude that varies as a function of a temperature of said current control means.

2. A medical instrument according to claim 1, wherein said current control means comprises a self-heating resistive device, having a resistance which decreases in proportion to increases in temperature of the device.

3. A medical instrument according to claim 2, further comprising:

(a) first switching means, connected between the source of energy and the energy storage means, for selectively coupling the source of energy with, and decoupling the source of energy from, the energy storage means; and

(b) second switching means, connected between the energy storage means and the connecting means, for selectively coupling the energy storage means with, and decoupling the energy storage means from, the pair of electrodes.

4. A medical instrument according to claim 2, wherein said current control means further comprises cooling means coupled to said resistive device for dissipating heat from said resistive device.

5. A medical instrument according to claim 4, wherein said cooling means comprises a plurality of fins made from aluminum.

6. A medical instrument according to claim 1, wherein said current control means comprises a thermistor having a negative temperature coefficient.

7. A medical instrument according to claim 1, further comprising shunt means, connected to said connecting means, for shunting a residual portion of the energy delivered from said energy storage means away from the patient when the energy storage means is connected to the pair of electrodes, wherein said residual portion has a magnitude that is a function of a temperature of said shunt means.

8. A medical instrument according to claim 7, wherein said shunt means comprises a resistive device, having a resistance which varies as a function of the temperature of the resistive device.

9. A medical instrument according to claim 7, wherein said shunt means comprises a negative temperature coefficient thermistor.

10. A medical instrument for generating and providing a pulse of electrical energy to a pair of electrodes that are attachable to a patient, the medical instrument comprising:

an energy source;

energy storage means, coupled to the energy source, for storing and discharging a predetermined quantity of energy;

a pair of electrodes that are attachable to the patient;

connecting means, connected to said energy storage means and connectable to the pair of electrodes, such that energy stored in said energy storage means is delivered from said energy storage means to the pair of electrodes; and

current control means, connected between said energy storage means and said pair of electrodes, for varying over time as a function of a temperature of said current control means a current which flows from said energy storage means to the pair of electrodes upon connection of the energy storage means to the pair of electrodes.

11. A medical instrument according to claim 10, further comprising shunt means, connected to said connecting means, for shunting a residual portion of the energy delivered from said energy storage means away from the pair of electrodes when said connecting means is connected to the pair of electrodes, wherein said residual portion has a magnitude that is a function of a temperature of the shunt means.

12. A medical instrument according to claim 10, further comprising inductive means connected between said energy storage means and said pair of electrodes, for storing and releasing a predetermined quantity of energy delivered upon the connection of said energy storage means to the pair of electrodes so as to increase the amount of time required for the energy delivered to the pair of electrodes to reach a peak value.

13. A medical instrument according to claim 10, further comprising cooling means coupled with said current control means for dissipating heat from said current control means.

14. A wave-shaping device in combination with a medical instrument that produces an energy pulse and delivers the energy pulse to a patient, the medical instrument including an energy source, energy storage means coupleable to the energy source for storing and discharging a predetermined quantity of energy and a pair of electrodes attachable to the patient, the wave-shaping device comprising:

self-heating current control means, connected between the energy storage means and the pair of electrodes, for varying a current waveform delivered from the energy storage means as a function of a temperature of said self-heating current control means; and

connecting means for connecting said self-heating current control means to the energy storage means and to the pair of electrodes.

15. A defibrillator for producing and delivering a defibrillation pulse to a patient comprising:

energy storage means for storing electrical energy;

electrode means, coupled with said energy storage means, for delivering a defibrillation pulse to the patient; and

circuit means, coupled with said energy storage means and including a resistive device, for controlling a flow of current delivered from the energy storage means as a function of a temperature of said resistive device so that the flow of said current from the energy storage means will vary over time in accordance with a predetermined waveform.

16. A defibrillator according to claim 15, wherein a resistance of said resistive device decreases as the temperature of the resistive device increases.

17. A defibrillator according to claim 15, further comprising shunt means for shunting a residual portion of the current delivered from the energy storage means away from said electrode means wherein said residual portion has a magnitude that is a function of a temperature of the shunt means.

18. A medical instrument including a pulse generation circuit for producing and delivering an energy pulse to a patient, comprising:

an energy source;

energy storage means, coupled to the energy source, for storing and discharging a predetermined quantity of energy;

connecting means, coupled to said energy storage means for connecting the energy storage means to a pair of electrodes that are attachable to the patient; and

shunt means, connected to said connecting means, for shunting a residual portion of the energy discharged by said energy storage means away from the pair of electrodes when the pair of electrodes is connected to said energy storage means, wherein the residual portion has a magnitude that varies as a function of a temperature of the shunt means.

19. A medical instrument according to claim 18, wherein said shut means comprises a resistive device, having a resistance which varies as a function of temperature of the resistive device.

20. A medical instrument for providing a pulse of energy having a biphasic current waveform to a pair of patient electrodes that are attachable to a patient, the instrument comprising:

an energy source;

energy storage means, coupleable to the energy source, for storing and discharging a pulse of energy;

a pair of patient electrodes that are attachable to a patient;

connecting means, connected to said energy storage means and connectable to the pair of patient electrodes, for carrying a pulse of energy discharged by said energy storage means to the pair of patient electrodes; and

current control means, connected between said energy storage means and said pair of patient electrodes, for shaping a pulse of energy discharged by said energy storage means as a function of a temperature of said current control means so that a current delivered by the pulse of energy initially has a magnitude of one polarity and then after a predetermined period of time has a magnitude of an opposite polarity.

21. A medical instrument according to claim 20, wherein said current control means comprises first and second thermistors coupled to the pair of patient electrodes so as to define a first current path, and third and fourth thermistors coupled to the pair of patient electrodes so as to define a second current path, said first and second thermistors having a negative temperature coefficient and said third and fourth thermistors having a positive temperature coefficient.

22. A medical instrument according to claim 20, wherein said current control means comprises a first pair of thermistors having a first set of thermal/resistive characteristics and a second pair of thermistors having a second set of thermal/resistive characteristics.

23. A wave-shaping circuit in combination with a medical instrument that produces and delivers an energy pulse to a patient, the medical instrument including energy storage means, coupleable to an energy source, for storing and discharging a pulse of energy, a pair of electrodes attachable to a patient and means for connecting the energy storage means to the pair of electrodes, the wave-shaping circuit comprising:

wave-shaping means, coupled with the energy storage means, for shaping pulses of energy discharged by the energy storage means over time as a function of a temperature of said wave-shaping means so that a current waveform delivered by each pulse varies biphasically; and

connecting means coupled with said wave-shaping means for connecting said wave-shaping means to the pair of electrodes.