Variable frequency impedance measurement

• US 20030236468A1
• Filed: 06/20/2002
• Published: 12/25/2003
• Est. Priority Date: 06/20/2002
• Status: Active Grant

• Current Assignee: Physio-Control Incorporated (Stryker Corporation)
• Original Assignee: Physio-Control Incorporated (Stryker Corporation)
• Inventors: Sullivan, Joseph L., Chapman, Fred W., Schweizer, Scott O.
• Granted Patent: US 8,417,327 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: A61N 1/3943 for threshold determination

Abstract

When a defibrillator selects a dosage of energy or current to be delivered to a patient, the defibrillator selects an excitation current frequency and applies the excitation current at the selected frequency to the patient. The frequency of the excitation current is selected as a function of the dosage to be delivered. The patient'"'"'s response to the excitation current at the selected frequency will accurately reflect the impedance that the defibrillator will “see” when delivering the selected dosage of energy or current.

Claims

1. A method comprising:

selecting a frequency of an excitation current as a function of a dosage of at least one of energy and defibrillation current to be delivered to a patient with a defibrillator;

applying the excitation current to the patient at the selected frequency; and

measuring an impedance of the patient by measuring a response of the patient to application of the excitation current.

2. The method of claim 1, wherein measuring an impedance of the patient comprises measuring an impedance of the patient by measuring a magnitude and a phase of the response of the patient to application of the excitation current.

3. The method of claim 1, further comprising:

delivering a defibrillation pulse to the patient; and

modulating the defibrillation pulse to deliver the dosage to the patient.

4. The method of claim 3, further comprising measuring an impedance of the patient by measuring a response of the patient to delivery of the defibrillation pulse.

5. The method of claim 1, further comprising selecting the dosage as a function of at least one of sex, age and body mass.

6. The method of claim 1, further comprising selecting the dosage as a function of a dosage of at least one of energy and defibrillation current delivered to the patient in a previous defibrillation pulse.

7. The method of claim 1, wherein selecting the frequency of the excitation current as a function of the dosage to be delivered to the patient with the defibrillator comprises selecting the frequency of the excitation current according to a formula that relates the frequency of the excitation current to the dosage.

8. The method of claim 1, wherein selecting the frequency of the excitation current as a function of the dosage to be delivered to the patient with the defibrillator comprises selecting the frequency from a lookup table.

9. The method of claim 1, further comprising storing energy in an energy storage device prior to delivery of the dosage to the patient.

10. The method of claim 1, wherein the frequency is a first frequency and the dosage is a first dosage, the method further comprising:

selecting a second dosage to be delivered to the patient with the defibrillator;

selecting a second frequency of the excitation current as a function of the second dosage;

applying the excitation current to the patient at the second selected frequency; and

measuring an impedance of the patient by measuring a response of the patient to application of the excitation current.

11. A defibrillator comprising:

a processor that selects a dosage of at least one of energy and defibrillation current to be delivered to a patient; and

a current source that generates an excitation current at a selectable frequency, the frequency of the excitation current being a function of the selected dosage.

12. The defibrillator of claim 11, further comprising an impedance measuring circuit that measures impedance of the patient as a function of the response of the patient to application of the excitation current to the patient.

13. The defibrillator of claim 12, the impedance measuring circuit comprising a voltage measurement device.

14. The defibrillator of claim 11, further comprising at least two electrodes that deliver the excitation current to the patient.

15. The defibrillator of claim 14, further comprising an impedance measuring circuit that measures the voltage across the electrodes and measures the impedance as a function of the voltage and the excitation current.

16. The defibrillator of claim 11, further comprising an energy storage device that stores energy for the dosage to be delivered to the patient.

17. The defibrillator of claim 11, wherein the processor selects the frequency of the excitation current as a function of the selected dosage.

18. The defibrillator of claim 11, wherein the current source generates the excitation current at a frequency selectable from at least three frequencies.

19. A method comprising:

applying a first excitation current at a first frequency to a patient;

measuring a first impedance of the patient by measuring a response of the patient to application of the first excitation current;

selecting a second frequency of a second excitation current as a function of the first measured impedance and a dosage of at least one of energy and defibrillation current to be delivered to the patient with a defibrillator.

20. The method of claim 19, further comprising:

applying the second excitation current to the patient at the selected frequency; and

measuring a second impedance of the patient by measuring a response of the patient to application of the excitation current.

21. The method of claim 20, further comprising selecting an excitation current function as a function of the first measured impedance.

22. The method of claim 21, wherein the excitation current function comprises an equation that relates excitation current frequency to an energy or current dosage. or lookup table

23. The method of claim 21, wherein the excitation current function comprises a lookup table that relates excitation current frequency to an energy or current dosage.

24. The method of claim 20, further comprising finding the difference between the first impedance and the second impedance.

25. A defibrillator comprising:

a current source that generates an excitation current at a selectable frequency;

at least two electrodes that deliver the excitation current to a patient at a selected frequency;

an impedance measuring circuit that measures the voltage across the electrodes and measures an impedance as a function of the voltage and the excitation current; and

a processor that selects the selected frequency of the excitation current as a function of a dosage of at least one of energy and defibrillation current to be delivered to the patient.

26. The defibrillator of claim 25, wherein the current source generates a first excitation current at a first frequency and a second excitation current at a second frequency, and wherein the impedance measuring circuit measures a first impedance associated with the excitation current at the first frequency and a second impedance associated with the excitation current at the second frequency.

27. The defibrillator of claim 26, wherein the processor selects the second selected frequency of an excitation current as a function of the first impedance.

28. The defibrillator of claim 25, wherein the processor selects a dosage of at least one of energy and defibrillation current to be delivered to the patient.