IMPLANTABLE TISSUE PERFUSION SENSING SYSTEM AND METHOD

• US 20080208067A1
• Filed: 02/28/2008
• Published: 08/28/2008
• Est. Priority Date: 02/28/2007
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Cinbis, Can, Carney, James K.
• Granted Patent: US 8,165,662 B2
• Time in Patent Office: Days
• US Class Current: 600/504
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting

Abstract

A medical device for sensing cardiac events that includes a plurality of electrodes sensing cardiac signals utilized to identify a cardiac event, a plurality of light sources capable of emitting light at a plurality of wavelengths, and a detector to detect the emitted light. A processor determines a plurality of light measurements in response to the emitted light detected by the detector, and generates a blood volume index in response to a light source of the plurality of light sources emitting light at an isobestic wavelength. The blood volume index is then utilized to verify the identifying of the cardiac event.

Claims

1. A medical device for sensing cardiac events, comprising:

a plurality of electrodes sensing cardiac signals utilized to identify a cardiac event;

a plurality of light sources capable of emitting light at a plurality of wavelengths;

a detector to detect the emitted light; and

a processor to determine a plurality of light measurements in response to the emitted light detected by the detector, to determine a blood volume index in response to determined light measurements of the plurality of light measurements from a light source of the plurality of light sources emitting light at an isobestic wavelength, and to verify the identifying of the cardiac event in response to the determined blood volume index.

2. The device of claim 1, wherein the processor corrects light measurements determined in response to the emitted light detected by the detector for effects of one or more of ambient light, tissue encapsulation, and mechanical motion.

3. The device of claim 2, wherein, during correcting of the light measurements, the processor generates an ambient light measurement in response to ambient light detected by the detector, and adjusts the determined light measurements in response to the ambient light measurement.

4. The device of claim 2, wherein, during correcting of the light measurements, the processor updates, for each of the plurality of wavelengths, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light, and adjusts the determined light measurements in response to the first normalization coefficient and the second normalization coefficient.

5. The device of claim 1, wherein the processor determines an isobestic baseline in response to light detected from the light source of the plurality of light sources emitting light at an isobestic wavelength at a predetermined time period.

6. The device of claim 5, wherein the processor determines the blood volume index by comparing a current light measurement to the isobestic baseline.

7. The device of claim 6, wherein the identifying of the cardiac event is verified in response to the blood volume index decreasing, relative to the isobestic baseline, by a predetermined threshold.

8. The device of claim 7, wherein the predetermined threshold corresponds to more than 2 percent over a ten second period.

9. The device of claim 6, wherein the processor determines a scaling factor corresponding to a light source other than the light source emitting light at the isobestic wavelength, and determines a second blood volume index for the light source other than the light source emitting light at the isobestic wavelength in response to a product of the scaling factor and the blood volume index determined for the light source emitting light at the isobestic wavelength.

10. The device of claim 5, wherein the isobestic baseline corresponds to a first light measurement from the light source of the plurality of light sources emitting light at an isobestic wavelength initiated during a current verifying of a cardiac event.

11. A method for verifying sensing of a cardiac event, comprising:

identifying the cardiac event in response to sensed cardiac signals;

determining light emitted by a plurality of light sources at a plurality of wavelengths;

determining a plurality of light measurements in response to the detected emitted light;

determining a blood volume index in response to a light source of the plurality of light sources emitting light at an isobestic wavelength; and

verifying the identifying of the cardiac event in response to the determined blood volume index.

12. The method of claim 11, further comprising correcting light measurements of the plurality of light measurements determined in response to the detected emitted light for effects of one or more of ambient light, tissue encapsulation, and mechanical motion.

13. The method of claim 12, further comprising:

generating, during the correcting of the light measurements, an ambient light measurement in response to ambient light detected by the detector; and

adjusting the determined light measurements in response to the ambient light measurement.

14. The method of claim 12, further comprising:

updating, during correcting of the light measurements, a first normalization coefficient and a second normalization coefficient in response to the detected emitted light; and

adjusting the determined light measurements in response to the first normalization coefficient and the second normalization coefficient for each of the plurality of wavelengths.

15. The method of claim 11, further comprising determining an isobestic baseline in response to light detected from the light source of the plurality of light sources emitting light at an isobestic wavelength at a predetermined time period.

16. The method of claim 15, further comprising:

comparing a current light measurement to the isobestic baseline; and

determining the blood volume index in response to the comparing.

17. The method of claim 15, further comprising verifying the cardiac event in response to the blood volume index decreasing, relative to the isobestic baseline, by a predetermined threshold.

18. The method of claim 17, wherein the predetermined threshold corresponds to more than 2 percent over a ten second period.

19. The method of claim 15, wherein the isobestic baseline corresponds to a first light measurement from the light source of the plurality of light sources emitting light at an isobestic wavelength initiated during a current verifying of a cardiac event.

20. The method of claim 16, further comprising:

determining a scaling factor corresponding to a light source other than the light source emitting light at the isobestic wavelength; and

determining a second blood volume index for the light source other than the light source emitting light at the isobestic wavelength in response to a product of the scaling factor and the blood volume index determined for the light source emitting light at the isobestic wavelength

21. A method for verifying sensing of a cardiac event, comprising:

identifying the cardiac event in response to sensed cardiac signals;

determining light emitted by a plurality of light sources at a plurality of wavelengths;

determining a plurality of light measurements in response to the detected emitted light;

determining an isobestic baseline (I_biso) in response to light detected from a light source of the plurality of light sources emitting light at an isobestic wavelength at a predetermined time period;

determining light measurements of the plurality of light measurements from the light source of the plurality of light sources emitting light at an isobestic wavelength at time t (I_iso(t));

determining a blood volume index as [I_iso(t)/I_biso]−

1; and

verifying the identifying of the cardiac event in response to the determined blood volume index.

22. The method of claim 21, wherein the cardiac event is verified in response to the blood volume index decreasing, relative to the isobestic baseline, by a predetermined threshold.