Implantable self-calibrating optical sensors

• US 7,840,246 B1
• Filed: 11/17/2005
• Issued: 11/23/2010
• Est. Priority Date: 09/20/2005
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Poore, John W.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US11/282,198
• Time in Patent Office: 1,832 Days
• Field of Search: 600309-344
• US Class Current: 600/339
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• 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 5/1495 Calibrating or testing of in-vivo probes

Abstract

A measurement light detector detects light transmitted by a light source of an implantable system that is scattered back into an implantable housing, and produces a measurement signal indicative of the intensity of the light detected by the measurement light detector. A calibration light detector detects a portion of the transmitted light that has not exited the housing, and produces a calibration signal that is indicative of the intensity of the light detected by the calibration light detector, which is indicative of the intensity of the light transmitted by the light source. Changes in the intensity of the transmitted light are compensated for based on the calibration signal produced by the calibration light detector. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims.

Claims

1. An implantable system, comprising:

an implantable housing comprising a window through which light can pass;

at least one light source, within said housing, each of which transmits light of a corresponding wavelength, wherein an intensity of the light transmitted by each said light source is controlled by a corresponding drive signal that drives said light source, and wherein a portion of the light of each said wavelength exits said housing through said window;

a measurement light detector, within said housing, to detect light of each said wavelength scattered back into said housing through said window, and to produce a measurement signal that is indicative of the intensity of the light of each said wavelength detected by said measurement light detector;

an opaque wall that separates said at least one light source from said measurement light detector;

a calibration light detector, within said housing on a same side of said opaque wall as said at least one light source, to detect a portion of the light of each said wavelength that has not exited said housing and has been reflected toward said calibration light detector without using a beam splitter, and to produce a calibration signal that is indicative of the intensity of the light of each said wavelength detected by said calibration light detector, which is indicative of the intensity of the light transmitted by each said light source; and

circuitry operative to detect changes in the intensity of the light transmitted by each said light source based on the calibration signal;

wherein said housing has an inner surface, a first portion of said inner surface coated with a reflective material to cause a portion of the light of each said wavelength that has not exited said housing to be reflected toward said calibration light detector, and a second portion of said inner surface not coated with the reflective material and corresponding to said window through which a portion of the light of each said wavelength exits said housing.

2. The system of claim 1, wherein said at least one light source comprises a single light source.

3. The system of claim 1, wherein said at least one light source comprises a first light source that transmits light of a first wavelength and a second light source that transmits light of a second wavelength.

4. The system of claim 3, wherein said at least one light source comprises a first, a second and a third light source, that transmit, respectively, light of a first wavelength, light of a second wavelength, and light of a third wavelength.

5. The system of claim 1, wherein said at least one light source comprises first and second spatially separated light sources that transmit light of about 805 nm, wherein said first light source is located closer to said measurement light detector than said second light source.

6. The system of claim 1, wherein the circuitry comprises a processor, state machine or random logic.

7. The system of claim 1, further comprising a processor configured to use the measurement signal to determine levels of blood oxygen saturation.

8. The system of claim 1, further comprising a processor configured to use the measurement signal to determine levels of hematocrit.

9. The system of claim 1, further comprising a processor configured to use the measurement signal to determine levels of blood oxygen saturation and levels of hematocrit.

10. The system of claim 1, wherein:

said opaque wall that separates said at least one light source from said measurement light detector prevents said measurement light detector from detecting internally reflected light or light transmitted directly from said at least one light source; and

said opaque wall does not prevent said calibration light detector from detecting internally reflected light or light transmitted directly from said at least one light source.

11. The system of claim 1, further comprising:

a substrate within said housing;

wherein said at least one light source and said calibration light detector are all attached to said substrate.

12. An implantable system, comprising:

an implantable housing including a window through which light can pass;

at least one light source, within said housing, each of which transmits light of a corresponding wavelength, and wherein a portion of the light of each said wavelength exits said housing through said window without being beam split;

a measurement light detector, within said housing, to detect light of each said wavelength scattered back into said housing through said window, and to produce a measurement signal that is indicative of the intensity of the light of each said wavelength detected by said measurement light detector;

an opaque wall that separates said at least one light source from said measurement light detector;

a calibration light detector positioned generally adjacent to said at least one light source, within said housing, on a same side of said opaque wall as said at least one light source; and

wherein a further portion of light of each said wavelength transmitted by said at least one light source is reflected so that it does not exit said housing and is detected by said calibration light detector, in response to which said calibration light detector produces a calibration signal that is indicative of the intensity of the light of each said wavelength detected by said calibration light detector, which is indicative of the intensity of the light transmitted by each said light source; and

wherein said housing has an inner surface, a first portion of said inner surface coated with a reflective material to cause a portion of the light of each said wavelength that has not exited said housing to be reflected toward said calibration light detector, and a second portion of said inner surface not coated with the reflective material and corresponding to said window through which a portion of the light of each said wavelength exits said housing.

13. The system of claim 12, further comprising:

a controller to adjust the measurement signal, based on the calibration signal, to compensate for changes in the intensity of the light transmitted by each said light source;

wherein said controller adjusts amplification of the measurement signal to compensate for changes in the intensity of each said light source due to aging of said light source.

14. The system of claim 12, further comprising:

a controller to adjust the measurement signal, based on the calibration signal, to compensate for changes in the intensity of the light transmitted by each said light source;

wherein said controller adjusts amplification by adjusting gain of an amplifier that amplifies the measurement signal.

15. The system of claim 12, further comprising:

a substrate within said housing;

wherein said at least one light source and said calibration light detector are all attached to said substrate.

16. The implantable system of claim 12, further comprising:

a controller to compensate for changes in the intensity of the transmitted light, based on the calibration signal.

17. For use in an implantable system, a method for compensating for changes in intensity of light transmitted by a light source of the implantable system, where the light source is contained within a housing having a window, the method comprising:

driving the light source with a drive signal to transmit light having an intensity that is controlled by the drive signal;

allowing a portion of the light transmitted by the light source to pass unsplit toward the window and out of the housing through the window, the window corresponding to a portion of an inner surface of the housing that is not coated by a reflective material;

detecting light scattered by blood;

producing, based on the detected light scattered by blood, a measurement signal indicative of the intensity of the detected light scattered by blood;

reflecting a further portion of the light toward a calibration detector generally adjacent to the light source, using a further portion of the inner surface of the housing that is coated with a reflective material, and detecting, without the use of a beam splitter, the further portion of the light transmitted by the light source that has not exited the housing within which the light source is contained;

producing a calibration signal that is indicative of the intensity of the detected light that has not exited the housing, which is indicative of the intensity of the light transmitted by the light source; and

compensating for changes in the intensity of the transmitted light, based on the calibration signal;

wherein the detecting of the further portion of the light is done using the calibration light detector that is on a same side of an opaque wall as the light source; and

wherein the detecting of the light scattered by blood is done using a measurement light detector that is on an opposite side of the opaque wall from the light source.

18. The method of claim 17, wherein the compensating step includes adjusting the drive signal, based on the calibration signal, to keep the intensity of the light transmitted by the light source substantially constant.

19. The method of claim 17, wherein the compensating step includes:

detecting changes in the intensity of the light transmitted by the light source based on the calibration signal; and

taking into account the detected changes in the intensity of the transmitted light when using the measurement signal for a diagnostic and/or therapeutic purpose.

20. The method of claim 19, further comprising using the measurement signal to determine levels of blood oxygen saturation and/or levels of hematocrit, wherein the detected changes in the intensity of the transmitted light are taken into account when using the measurement signal to determine levels of blood oxygen saturation and/or levels of hematocrit.

21. The method of claim 17, wherein the compensating step includes adjusting the measurement signal, based on the calibration signal, to compensate for changes in the intensity of the light transmitted by the light source.