Voltage independent measurement apparatus, system, and method

• US 20040111125A1
• Filed: 12/09/2002
• Published: 06/10/2004
• Est. Priority Date: 12/09/2002
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Stessman, Nicholas J.
• Granted Patent: US 7,039,464 B2
• Time in Patent Office: Days
• US Class Current: 607/27
• CPC Class Codes: A61N 1/3708 for power depletion

Abstract

A cardiac rhythm management apparatus may include a monitored energy source, a reference energy source, and a measurement module. The monitored source provides an initial pacing amplitude voltage and a pacing droop voltage, while the reference source provides a substantially fixed reference voltage. The measurement module, coupled to the monitored source and the reference source, provides a measurement related to the lead impedance associated with the rhythm management apparatus that is substantially independent of the reference voltage. Thus, a system may include the apparatus coupled to a lead wire. An article may cause a machine to implement a method which operates to determine a ratio of the actual initial pacing amplitude voltage to the actual pacing droop voltage.

Claims

1. An apparatus, comprising:

a monitored energy source providing a first indication associated with an actual initial pacing voltage and a second indication associated with a actual pacing droop voltage;

a reference energy source to provide a reference indication; and

a measurement module coupled to the monitored energy source and the reference energy source, the measurement module to provide a third indication associated with a ratio of the first indication and the second indication, the ratio being substantially independent of the reference indication.

2. The apparatus of claim 1, wherein the measurement module comprises:

a sampler to sample a sum of the first indication and the reference indication; and

a converter coupled to the sampler, the converter to generate the third indication derived from the sum.

3. The apparatus of claim 2, wherein the sum is substantially equal to the sum of the actual initial pacing voltage and a reference voltage associated with the reference indication.

4. The apparatus of claim 2, wherein the sampler and the converter are included in a successive approximation analog to digital converter.

5. The apparatus of claim 4, wherein the third indication is stored in a successive approximation register included in the analog to digital converter.

6. The apparatus of claim 1, wherein the first indication is substantially equal to the actual initial pacing voltage, wherein the second indication is substantially equal to the actual pacing droop voltage, and wherein the reference indication is substantially equal to a reference voltage.

7. The apparatus of claim 1, wherein the monitored energy source comprises:

a pacing supply capacitor.

8. A system, comprising:

an apparatus, including a monitored energy source providing a first indication associated with an actual initial pacing voltage and a second indication associated with an actual pacing droop voltage, a reference energy source to provide a reference indication value, and a measurement module coupled to the monitored energy source and the reference energy source, the measurement module to provide a third indication associated with a ratio of the first indication and the second indication, the ratio being substantially independent of the reference indication; and

a lead wire electrically coupled to the measurement module.

9. The system of claim 8, wherein the monitored energy source comprises:

a pacing voltage generator coupled to a pacing supply capacitor.

10. The system of claim 8, wherein the third indication is approximately proportional to an impedance associated with at least one of a plurality of electrodes coupled to the lead wire.

11. The system of claim 8, further comprising:

an attenuator electrically coupled between the monitored energy source and the measurement module, wherein the attenuator is capable of attenuating a magnitude associated with the actual initial pacing voltage by a factor of K≦

1.0.

12. The system of claim 8, wherein the measurement module includes a plurality of capacitors arranged in a successive approximation sampling configuration.

13. The system of claim 12, further comprising:

control logic coupled to the plurality of capacitors.

14. The system of claim 8, wherein the reference energy source provides a substantially fixed voltage value.

15. A method, comprising:

determining a first sum of an actual initial pacing voltage and a reference indication;

determining a second sum of an actual pacing droop voltage and the reference indication; and

determining a ratio of the first sum and the second sum which is substantially independent of the reference indication.

16. The method of claim 15, wherein determining a first sum of an actual initial pacing voltage and a reference indication comprises:

sampling a first amplitude value proportional to the actual initial pacing voltage; and

sampling a second amplitude value proportional to the reference indication.

17. The method of claim 16, wherein the first amplitude value is approximately equal to a magnitude of the actual initial pacing voltage.

18. The method of claim 16, wherein sampling a first amplitude value proportional to the actual initial pacing voltage comprises:

sampling the actual initial pacing voltage using a plurality of capacitors arranged in a successive approximation sampling configuration.

19. The method of claim 16, wherein sampling a second amplitude value proportional to the reference indication comprises:

sampling a substantially fixed voltage value provided by a reference energy source.

20. The method of claim 15, wherein determining a ratio of the first sum and the second sum which is substantially independent of the reference indication comprises:

balancing a charge sampled onto a reference capacitor against a charge sampled onto a plurality of other capacitors.

21. The method of claim 15, further comprising:

attenuating a value associated with the actual initial pacing voltage.

22. An article comprising a machine-accessible medium having associated data, wherein the data, when accessed, results in a machine performing:

determining a first sum of an actual initial pacing voltage and a reference indication;

determining a second sum of an actual pacing droop voltage and the reference indication; and

determining a ratio of the first sum and the second sum which is substantially independent of the reference indication.

23. The article of claim 22, wherein the machine-accessible medium further includes data, which when accessed by the machine, results in the machine performing:

providing the actual initial pacing voltage across a pacing supply capacitor.

24. The article of claim 23, wherein the machine-accessible medium further includes data, which when accessed by the machine, results in the machine performing:

providing the actual pacing droop voltage across the pacing supply capacitor.

25. The article of claim 22, wherein determining a first sum of an actual initial pacing voltage and a reference indication comprises:

accumulating a charge on a reference capacitor proportional to a sum of the actual initial pacing voltage and the reference indication.

26. The article of claim 25, wherein determining a ratio of the first sum and the second sum which is substantially independent of the reference indication comprises:

transferring the charge on the reference capacitor proportional to the sum of the actual initial pacing voltage and the reference indication to at least one other capacitor.

27. A method, comprising:

determining an actual initial pacing voltage;

determining an actual pacing droop voltage; and

determining a ratio of the actual initial pacing voltage to the actual pacing droop voltage by balancing accumulated charges, wherein the ratio is substantially independent of a reference indication.