Cardiac cycle synchronized sampling of impedance signal

• US 8,442,633 B2
• Filed: 10/30/2012
• Issued: 05/14/2013
• Est. Priority Date: 07/02/2003
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Kim, Jaeho, Ni, Quan
• Primary Examiner(s): Layno, Carl H
• Assistant Examiner(s): Porter, Jr., Allen
• Application Number:
  US13/663,647
• Publication Number:
  US 20130053705A1
• Time in Patent Office: 196 Days
• Field of Search: 607/17, 607/18, 607 2- 9, 607/42
• US Class Current: 607/18
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61N 1/3601 of respiratory organs
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators

Abstract

A system comprising implantable device, the implantable medical device including an intrinsic cardiac signal sensor, an impedance measurement circuit configured to apply a specified current to a transthoracic region of a subject and to sample a transthoracic voltage resulting from the specified current, and a processor coupled to the intrinsic cardiac signal sensor and the impedance measurement circuit. The processor is configured to initiate sampling of a transthoracic voltage signal in a specified time relation to a fiducial marker in a sensed intrinsic cardiac signal, wherein the sampling attenuates or removes variation with cardiac stroke volume from the transthoracic voltage signal, and determine lung respiration using the sampled transthoracic voltage signal.

Claims

1. A system comprising implantable device, the implantable medical device including:

an intrinsic cardiac signal sensor;

an impedance measurement circuit configured to apply a specified current to a transthoracic region of a subject and to sample a transthoracic voltage resulting from the specified current; and

a processor, coupled to the intrinsic cardiac signal sensor and the impedance measurement circuit, the processor configured to;

initiate sampling of a transthoracic voltage signal synchronous to an occurrence of a fiducial marker in a sensed intrinsic cardiac signal, wherein the sampling attenuates or removes variation with cardiac stroke volume from the transthoracic voltage signal; and

determine lung respiration using the sampled transthoracic voltage signal.

2. The system of claim 1, wherein the processor is configured to initiate sampling to produce a sampled transthoracic voltage signal having a cardiac stroke volume signal component that has a substantially constant value.

3. The system of claim 1, wherein the processor is configured to:

initiate sampling to preserve a respiratory component of the transthoracic voltage signal; and

determine lung ventilation using the respiratory component of the transthoracic voltage signal.

4. The system of claim 1, wherein the processor is configured to initiate sampling of the transthoracic voltage signal synchronously with an occurrence of an R-wave in the sensed intrinsic cardiac signal.

5. The system of claim 1, wherein the processor is configured to:

convert sampled transthoracic voltage signal values to transthoracic impedance values; and

calculate lung ventilation using the transthoracic impedance values.

6. The system of claim 1,

wherein the transthoracic voltage signal includes a cardiac stroke volume component having a first frequency and includes a low frequency component having a second frequency lower than the first frequency;

wherein the processor is configured to;

initiate sampling to preserve a low frequency component of the transthoracic voltage signal; and

convert the low frequency component of the transthoracic voltage signal to a low frequency component of a transthoracic impedance signal.

7. The system of claim 1, wherein the impedance measurement circuit is configured to measure the transthoracic voltage using a transthoracic measurement vector that includes an atrium of the subject.

8. The system of claim 1, wherein the impedance measurement circuit is configured to measure the transthoracic voltage using a transthoracic measurement vector that includes a ventricle of the subject.

9. The system of claim 1, wherein the impedance measurement circuit is configured to sample an unfiltered transthoracic voltage signal.

10. The system of claim 1, including:

a memory integral to or electrically coupled to the processor, wherein the processor is configured to;

store a sampled value of transthoracic voltage in a synchronous relation to the occurrence of the fiducial marker in the sensed intrinsic cardiac signal, and

increase a rate of storing sampled values of transthoracic voltage as the rate of occurrence of the fiducial marker increases.

11. A method comprising:

applying a specified current to a transthoracic region of a subject;

sampling a transthoracic voltage signal resulting from the specified current, wherein the sampling occurs synchronously to an occurrence of a fiducial marker in a sensed intrinsic cardiac signal and attenuates or removes variation with cardiac stroke volume from the transthoracic voltage signal; and

determining lung respiration using the sampled transthoracic voltage signal.

12. The method of claim 11, wherein sampling a transthoracic voltage signal includes sampling to produce a sampled transthoracic voltage signal having a cardiac stroke volume signal component that is a substantially constant value.

13. The method of claim 11,

wherein sampling a transthoracic voltage signal includes sampling to preserve a respiratory component of the transthoracic voltage signal, and

wherein determining lung respiration includes determining lung ventilation using the respiratory component of the transthoracic voltage signal.

14. The method of claim 11, wherein sampling a transthoracic voltage signal includes sampling the transthoracic voltage signal synchronously with an occurrence of an R-wave in the sensed intrinsic cardiac signal.

15. The method of claim 11, including:

converting sampled transthoracic voltage signal values to transthoracic impedance values; and

calculating lung ventilation using the transthoracic impedance values.

16. The method of claim 11,

wherein the transthoracic voltage signal includes a cardiac stroke volume component having a first signal frequency and includes a low frequency component having a second signal frequency lower than the first signal frequency,

wherein sampling a transthoracic voltage signal includes sampling to preserve a low frequency component of the transthoracic voltage signal, and

wherein the method includes converting the low frequency component of the transthoracic voltage signal to a low frequency component of a transthoracic impedance signal.

17. The method of claim 11, wherein sampling a transthoracic voltage signal includes storing a sampled value of transthoracic voltage in a synchronous relation to the fiducial marker in the sensed intrinsic cardiac signal.

18. The method of claim 11,

wherein applying a specified current and sampling a transthoracic voltage signal includes applying the specified current and sampling the transthoracic voltage signal using a first combination of electrodes, and

wherein the method includes changing, in response to determining signal noise in the transthoracic voltage signal, to a second combination of electrodes for applying the specified current and sampling the transthoracic impedance.

19. The method of claim 11, wherein a frequency of occurrence of the fiducial marker in the cardiac signal increases with heart rate of the subject, and wherein sampling a transthoracic voltage signal includes increasing a sampling frequency of the transthoracic voltage signal with the increase in heart rate.

20. The method of claim 11, including:

determining that lung respiration is below a specified lung respiration level; and

initiating delivery of sleep apnea therapy in response to the determination.