Method and apparatus for delivering electrotherapy having an equivalent probability of success for different patients

• US 6,650,936 B2
• Filed: 04/23/2001
• Issued: 11/18/2003
• Est. Priority Date: 04/23/2001
• Status: Expired due to Term

• Current Assignee: Physio-Control Incorporated (Stryker Corporation)
• Original Assignee: Medtronic Physio-Control Manufacturing Corp. (Medtronic Plc)
• Inventors: DeBardi, Gary, Sullivan, Joseph L.
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US09/841,183
• Publication Number:
  US 20020183790A1
• Time in Patent Office: 939 Days
• Field of Search: 607/5-8, 607/27-28
• US Class Current: 607/6
• CPC Class Codes: A61N 1/3943 for threshold determination

Abstract

A medical device constructed according to the invention includes electrodes (12a, 12b), a measuring unit (24) for measuring a patient-dependent electrical parameter (e.g., impedance) of the patient, an electrotherapy generator (26) for delivering electrotherapy to the patient, and a processing unit (20) for controlling the delivery of electrotherapy to the patient. Electrotherapy is preferably delivered to the patient based on the measured patient-dependent electrical parameter and a predetermined response of a reference patient to a nominal electrotherapy. The actual electrotherapy delivered to the patient is controlled so that the electrotherapy has a probability of success for the patient that is equivalent to the probability of success of the nominal electrotherapy for the reference patient. A consistent shock efficacy across different patients is achieved.

Claims

1. A medical device for delivering electrotherapy comprising:

(a) electrodes adapted to be placed on a patient;

(b) a measuring unit in communication with the electrodes for measuring a patient-dependent electrical parameter of the patient;

(c) an electrotherapy generator in communication with the electrodes for delivering electrotherapy to the patient;

(d) a processing unit in communication with the measuring unit and the electrotherapy generator for controlling the electrotherapy that is delivered to the patient, wherein the processing unit is configured to cause the electrotherapy generator to deliver an electrotherapy that is adjusted for the patient based on the patient'"'"'s measured patient-dependent electrical parameter, the electrotherapy being adjusted in accordance with the measured patient-dependent electrical parameter to have an equivalent probability of success in substantially all patients.

2. The medical device of claim 1, wherein the patient-dependent electrical parameter is impedance.

3. The medical device of claim 2, wherein the impedance is transthoracic impedance.

4. The medical device of claim 1, wherein the patient is a present patient, and wherein the electrotherapy for the present patient is adjusted from a nominal electrotherapy, the adjustment using the present patient'"'"'s measured patient-dependent electrical parameter and a predetermined response of a reference patient to the nominal electrotherapy to produce electrotherapy for the present patient having a probability of success equivalent to the probability of success of the nominal electrotherapy for the reference patient.

5. The medical device of claim 4, wherein the predetermined response of the reference patient is based on a quantitative model, and wherein the electrotherapy for the present patient produces a model response in the present patient that is equivalent to the predetermined model response of the reference patient to the nominal electrotherapy.

6. The medical device of claim 4, wherein the adjustment is derived from a predetermined translation factor that, when applied to the nominal electrotherapy, translates the nominal electrotherapy to the electrotherapy for the present patient.

7. The medical device of claim 6, wherein the predetermined translation factor is derived from:

(a) comparing the predetermined model response of the reference patient to the nominal electrotherapy with the model response of a range of different patients to the nominal electrotherapy; and

(b) compensating for relative differences in model response between the reference patient and the different patients so that the translation factor, when applied to the nominal electrotherapy, results in electrotherapy that produces an equivalent model response in the different patients.

8. The medical device of claim 1, wherein the electrotherapy generator includes an energy storage device from which the electrotherapy is delivered to the patient, and wherein the electrotherapy for the patient is adjusted by adjusting the charge level to which the energy storage device is charged.

9. The medical device of claim 8, wherein the adjustment to the charge level of the energy storage device is made after charging the energy-storing device has commenced.

10. A method of delivering electrotherapy, comprising:

(a) selecting a nominal electrotherapy for a present patient;

(b) determining the response of a reference patient to the nominal electrotherapy, the reference patient having a patient-dependent electrical parameter of a reference amount;

(c) measuring a patient-dependent electrical parameter in the present patient that corresponds to the reference patient-dependent electrical parameter; and

(d) controlling the delivery of electrotherapy to the present patient based on the present patient'"'"'s measured patient-dependent electrical parameter and the determined response of the reference patient to produce an actual electrotherapy that, when delivered to the present patient, has a probability of success for the present patient that is equivalent to the probability of success of the nominal electrotherapy for the reference patient.

11. The method of claim 10, further comprising storing an electrical charge in a capacitor and connecting the capacitor to the present patient to deliver the actual electrotherapy, wherein the delivery of the actual electrotherapy to the present patient is controlled by controlling the charge level to which the capacitor is charged.

12. The method of claim 11, further comprising:

(a) commencing to charge the capacitor to a nominal charge level designed for delivering the nominal electrotherapy to the reference patient; and

(b) adjusting the charge level of the capacitor from the nominal charge level to an actual charge level based on the measured patient-dependent electrical parameter of the present patient.

13. The method of claim 10, wherein the patient-dependent electrical parameter of the reference patient and the corresponding patient-dependent electrical parameter of the present patient is impedance.

14. The method of claim 13, wherein the impedance is transthoracic impedance.

15. The method of claim 10, wherein the determined response of the reference patient is based on a quantitative model, and wherein the actual electrotherapy to be delivered to the present patient is controlled to produce a model response in the present patient that is equivalent to the determined model response of the reference patient to the nominal electrotherapy.

16. The method of claim 15, further comprising:

(a) using the quantitative model, determining a model response of a range of different patients to the nominal electrotherapy, the different patients having a corresponding patient-dependent electrical parameter of an amount different than the reference amount of the reference patient;

(b) comparing the determined model response of the reference patient to the determined model response of the range of different patients; and

(c) determining a translation factor that compensates for relative differences in model response between the reference patient and the different patients to the nominal electrotherapy, so that when applied to the nominal electrotherapy, the translation factor translates the nominal electrotherapy to actual electrotherapy that produces an equivalent model response in the different patients.

17. The method of claim 16, wherein the translation factor uses the measured patient-dependent electrical parameter of the present patient to define an adjustment that is applied to the nominal electrotherapy to produce the actual electrotherapy for the present patient.

18. A medical device for delivering electrotherapy, comprising:

(a) electrodes adapted to be placed on a present patient;

(b) an impedance measuring unit in communication with the electrodes for measuring an impedance of the present patient;

(c) an electrotherapy generator in communication with the electrodes for delivering electrotherapy to the present patient; and

(d) a processing unit in communication with the impedance measuring unit and the electrotherapy generator for controlling the electrotherapy that is delivered to the present patient, wherein the processing unit is configured to cause the electrotherapy generator to deliver an actual electrotherapy to the present patient based on the present patient'"'"'s measured impedance and a predetermined response of a reference patient to a nominal electrotherapy, the processing unit controlling the electrotherapy generator so that the actual electrotherapy delivered to the present patient has a probability of success for the present patient that is equivalent to the probability of success of the nominal electrotherapy for the reference patient.

19. The medical device of claim 18, wherein the medical device is a defibrillator and the electrotherapy delivered from the electrotherapy generator is a defibrillation pulse.

20. The medical device of claim 18, wherein the electrotherapy generator includes a capacitor for storing a charge from which the electrotherapy is produced, and wherein the processing unit controls the electrotherapy by controlling the charge level to which the capacitor is charged.

21. The medical device of claim 20, wherein the electrotherapy generator commences charging the capacitor to a nominal charge level designed for the nominal electrotherapy and after measuring the present patient'"'"'s impedance, adjusts the charge level of the capacitor to produce the actual electrotherapy.

22. The medical device of claim 18, wherein the predetermined response of the reference patient is based on a quantitative model, and wherein the actual electrotherapy is designed to produce a model response in the present patient that is equivalent to the predetermined response of the reference patient to the nominal electrotherapy.

23. The medical device of claim 22, wherein the processing unit uses a translation factor to control the actual electrotherapy that is delivered to the present patient, the translation factor translating the nominal electrotherapy designed for the reference patient to the actual electrotherapy designed for the present patient.

24. The medical device of claim 23, wherein the translation factor uses the present patient'"'"'s measured impedance to define an adjustment that is applied to the nominal electrotherapy to produce the actual electrotherapy.

25. The medical device of claim 23, wherein the translation factor is derived by:

(a) comparing the predetermined response of the reference patient to the nominal electrotherapy with the model response of a range of different impedance patients to the nominal electrotherapy; and

(b) determining an adjustment that compensates for relative differences in model response between the reference patient and the different impedance patients so that the adjustment, when applied to the nominal electrotherapy, results in an actual electrotherapy that produces an equivalent model response in the different impedance patients.

26. A method of determining a translation factor for use in an electrotherapy device that produces electrotherapy for different patients having an equivalent probability of success for the different patients, the method comprising:

(a) preparing a quantitative model of an electrotherapy device/patient system defined by the electrotherapy device attached to a patient, the quantitative model including a patient-dependent electrical parameter for the patient;

(b) selecting a nominal electrotherapy;

(c) using the quantitative model, determining the model response of a reference patient in the electrotherapy device/patient system to the nominal electrotherapy, the patient-dependent electrical parameter for the reference patient having a reference amount;

(d) using the quantitative model, determining the model response of different patients in the electrotherapy device/patient system to the nominal electrotherapy, the patient-dependent electrical parameter for the different patients having amounts different than the reference amount;

(e) comparing the model response of the reference patient with the model response of the different patients to the nominal electrotherapy; and

(f) determining the translation factor to provide an adjustment for the different patients that compensates for relative differences between the model response of the reference patient and the model response of the different patients to the nominal electrotherapy, the adjustment modifying the nominal electrotherapy to define an actual electrotherapy that, when delivered to a patient, produces a model response in the patient that is equivalent to the model response of the reference patient to the nominal electrotherapy.

27. The method of claim 26, wherein the translation factor is an equation that uses a measured patient-dependent electrical parameter of a present patient to define the adjustment that modifies the nominal electrotherapy to produce the actual electrotherapy for the present patient.

28. The method of claim 26, wherein the patient-dependent electrical parameter is impedance.

29. The method of claim 28, wherein the impedance is transthoracic impedance.

30. A defibrillator comprising:

(a) electrodes adapted for placement on a patient;

(b) a measuring unit in communication with the electrodes for measuring a patient-dependent electrical parameter of the patient;

(c) an electrotherapy generator in communication with the electrodes for delivering multiphasic defibrillation therapy to the patient; and

(d) a processing unit in communication with the measuring unit and the electrotherapy generator for controlling the defibrillation therapy that is delivered to the patient, wherein the processing unit is configured to cause the electrotherapy generator to deliver multiphasic defibrillation therapy having an amplitude and phase duration that are determined based on the measured patient-dependent electrical parameter to produce defibrillation therapy having an equivalent probability of success for the patient as for other patients, the defibrillation therapy delivering an amount of energy to the patient that is increased or decreased in relation to a corresponding increase or decrease of the measured patient-dependent electrical parameter of the patient.

31. The defibrillator of claim 30, wherein the patient-dependent electrical parameter is impedance, and wherein the amount of energy delivered to the patient is increased if the patient'"'"'s measured impedance is higher than a nominal reference impedance, and the amount of energy delivered is decreased if the patient'"'"'s measured impedance is lower than the nominal reference impedance.

32. The defibrillator of claim 30, wherein the electrotherapy generator includes a capacitor for storing a charge from which the defibrillation therapy is produced, and wherein the processing unit controls the amplitude of the multiphasic defibrillation therapy by controlling the charge level to which the capacitor is charged.

33. The defibrillator of claim 32, wherein the capacitor is charged to an actual charge level determined using the measured patient-dependent electrical parameter to calculate an adjustment that, when applied to a nominal charge level, translates the nominal charge level to the actual charge level.

34. The defibrillator of claim 33, wherein the actual charge level causes the capacitor, upon discharge, to deliver defibrillation therapy that produces in the patient a model response that is equivalent to the model response of a reference patient to defibrillation therapy produced from charging the capacitor to the nominal charge level.

35. The defibrillator of claim 30, wherein the phase duration is determined prior to delivery of the defibrillation therapy to minimize the leading edge voltage of the defibrillation therapy for successful defibrillation.

36. The defibrillator of claim 30, wherein the phase duration is determined during delivery of the defibrillation therapy based on a patient-dependent parameter observed during the defibrillation therapy.

37. The defibrillator of claim 30, wherein the defibrillation therapy delivers to the patient an initial defibrillation current that, relative to the initial defibrillation current that would be delivered to a reference patient of 80 ohms, is approximately 45% higher for a 40 ohm patient, 15% higher for a 60 ohm patient, 7% lower for a 100 ohm patient, and 16% lower for a 120 ohm patient.

38. The defibrillator of claim 30, wherein the processing unit controls the amplitude and phase duration of the first phase of the multiphasic defibrillation therapy to deliver to the patient an amount of charge in the first phase that is equivalent for all patients.