Method and apparatus for providing variable defibrillation waveforms using switch-mode amplification

• US 6,208,896 B1
• Filed: 11/13/1998
• Issued: 03/27/2001
• Est. Priority Date: 11/13/1998
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Mulhauser, Daniel F.
• Primary Examiner(s): Schaetzle, Kennedy
• Application Number:
  US09/191,662
• Time in Patent Office: 865 Days
• Field of Search: 607/5, 607/7, 607/4, 607/74
• US Class Current: 607/5
• 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: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

A method and apparatus for providing variable defibrillation waveforms using switch-mode amplification are provided. In one embodiment, a defibrillation waveform generator is described that includes a rapid-discharge capacitor, a controller, and a switch-mode amplifier. The rapid-discharge capacitor is charged to a charge voltage that may be discharged over a time frame consistent with the chronaxie time of a human heart. The controller generates at least one control signal, which may be pulse-width modulated. The switch-mode amplifier responsive to the control signals, optionally supplemented by a biphasic converter, selectively amplifies the charge voltage so that the magnitude, phase, and timing of the amplification may be varied, thus resulting in a variable waveform. In some embodiments, the present invention includes both step-up and step-down converters. The step-down converter enables the defibrillator to be used so that the rapid-discharge energy storage device is charged to a charge voltage that is greater than the output voltage applied to the defibrillation patient. The step-up converter is used to maintain or increase the output voltage as the charge voltage is depleted. The step-up and step-down converters of the switch-mode amplifier may be employed in either order, i.e., step-down followed by step-up, or step-up followed by step-down. A step-down followed by step-up topology may permit the use of fewer components, or fewer of certain types of components. A step-up followed by step-down topology provides a constant-current source that may produce a particularly efficacious electrotherapeutic effect.

Claims

1. A defibrillation waveform generator for generating a defibrillator waveform using a defibrillation voltage from a voltage generator, the defibrillation waveform generator comprising:

a rapid-discharge energy storage device charged by the voltage generator so as to store a charge voltage, the rapid-discharge energy storage device tuned consistently with a chronaxie time of a human heart;

a controller constructed and arranged to generate at least one control signal; and

an amplifier, responsive to one or more of the control signals, constructed and arranged to selectively amplify the charge voltage so as to enable generation of a variable defibrillation waveform.

2. The defibrillation waveform generator of claim 1, wherein:

the amplifier is a switch-mode amplifier.

3. The defibrillation waveform generator of claim 2, wherein:

the amplifier comprises

a step-up converter having at least one boost switch responsive to a first control signal, constructed and arranged to selectively amplify the charge voltage to generate an amplified voltage.

4. The defibrillation waveform generator of claim 3, further comprising:

a feedback sensor, constructed and arranged to provide at least one system-performance parameter to the controller; and

wherein the controller is further constructed and arranged to determine at least one waveform-reference parameter;

compare the system-performance parameter to the waveform-reference parameter to determine at least one error value; and

modify the first control signal to reduce the error value.

5. The defibrillation waveform generator of claim 3, wherein:

the amplifier further comprises

a step-down converter having at least one buck switch responsive to a second control signal, constructed and arranged to selectively decrease the charge voltage.

6. The defibrillation waveform generator of claim 5, wherein:

the at least one boost switch and the at least one buck switch are the same switch.

7. The defibrillation waveform generator of claim 5, further comprising:

a feedback sensor, constructed and arranged to provide at least one system-performance parameter to the controller; and

wherein the controller is further constructed and arranged to

determine at least one waveform-reference parameter;

compare the system-performance parameter to the waveform-reference parameter to determine at least one error value;

modify the first control signal to reduce the error value; and

modify the second control signal to reduce the error value.

8. The defibrillation waveform generator of claim 3, wherein:

the amplifier further comprises

a step-down converter having at least one buck switch responsive to a second control signal, constructed and arranged to selectively decrease the amplified voltage.

9. The defibrillation waveform generator of claim 3, further comprising:

a biphasic converter constructed and arranged to biphasically convert the amplified voltage to provide a biphasic output voltage.

10. The defibrillation waveform generator of claim 9, wherein:

the biphasic converter is an H-bridge.

11. The defibrillation waveform generator of claim 9, wherein:

the biphasic converter is a push-pull amplifier.

12. The defibrillation waveform generator of claim 10, wherein:

the step-up converter and the H-bridge share at least one switch.

13. The defibrillation waveform generator of claim 3, further comprising:

a waveform definer constructed and arranged to provide to the controller at least one reference parameter of at least one defibrillation waveform.

14. The defibrillation waveform generator of claim 13, further comprising:

an initial impedance sensor constructed and arranged to provide to the waveform definer an indicator of an initial patient impedance.

15. The defibrillation waveform generator of claim 3, further comprising:

an initial impedance sensor constructed and arranged to provide to the controller an indicator of an initial patient impedance.

16. The defibrillation waveform generator of claim 2, wherein:

the amplifier comprises

a step-down converter, constructed and arranged to selectively decrease the charge voltage to generate a step-down voltage, having at least one buck switch responsive to a second control signal, and

a step-up converter, constructed and arranged to selectively amplify the step-down voltage to generate an amplified voltage, having at least one boost switch responsive to a first control signal.

17. The defibrillation waveform generator of claim 16, wherein:

the step-down converter and the step-up converter share an inductor.

18. The defibrillation waveform generator of claim 16, wherein:

the step-down converter and the step-up converter share a capacitor.

19. The defibrillation waveform generator of claim 16, further comprising:

a feedback sensor, constructed and arranged to sense an indicator of patient impedance provided by the step-up converter, electrically coupled to the controller.

20. The defibrillation waveform generator of claim 16, further comprising:

a feedback sensor, constructed and arranged to sense an indicator of patient impedance provided by the step-down converter, electrically coupled to the controller.

21. A defibrillator, comprising:

a power supply,

a defibrillation voltage generator electrically coupled to the power supply, constructed and arranged to generate a defibrillation voltage; and

a defibrillation waveform generator for generating a defibrillator waveform, the defibrillation waveform generator including;

a rapid-discharge energy storage device having a charge voltage, electrically coupled to the defibrillation voltage generator;

a controller constructed and arranged to generate at least one control signal; and

an amplifier, responsive to one or more of the control signals, constructed and arranged to selectively amplify the charge voltage so as to enable generation of a variable defibrillation waveform.

22. The defibrillator of claim 21, wherein:

the amplifier is a switch-mode amplifier.

23. The defibrillator of claim 22, wherein:

the amplifier comprises

a step-up converter having at least one boost switch responsive to a first control signal, constructed and arranged to selectively amplify the charge voltage to generate an amplified voltage.

24. The defibrillator of claim 22, wherein:

the amplifier comprises

a step-down converter, constructed and arranged to selectively decrease the charge voltage to generate a step-down voltage, having at least one buck switch responsive to a second control signal, and

a step-up converter, constructed and arranged to selectively amplify the step-down voltage to generate an amplified voltage, having at least one boost switch responsive to a first control signal.

25. The defibrillator of claim 21, wherein:

the defibrillation waveform generator is externally coupleable to a human being.

26. The defibrillator of claim 21, wherein:

the defibrillation waveform generator is implantable within a human being.

27. A method for generating a defibrillator waveform, comprising:

charging a rapid-discharge energy storage device to a charge voltage, wherein the storage device is tuned consistently with a chronaxie time of a human heart;

generating at least one control signal; and

selectively amplifying the charge voltage responsive to one or more of the control signals so as to enable generation of a variable defibrillation waveform.

28. The method of claim 27, wherein:

the generating step comprises;

generating a pulse-width modulated control signal.

29. The method of claim 27, wherein:

the generating step comprises;

generating a pulse-frequency modulated control signal.

30. The method of claim 27, wherein:

the selectively amplifying step comprises;

switch-mode amplifying.

31. The method of claim 27, wherein:

the selectively amplifying step comprises

step-up converting for selectively maintaining the charge voltage.

32. The method of claim 31, further wherein:

the selectively amplifying step comprises

step-down converting for selectively decreasing the charge voltage, wherein the step up converting is responsive to a first control signal and the step-down converting is responsive to a second control signal.