Method and Apparatus for Sensing Blood Oxygen

• US 20090069652A1
• Filed: 09/07/2007
• Published: 03/12/2009
• Est. Priority Date: 09/07/2007
• Status: Active Grant

• Current Assignee: Nielsen Consumer LLC (Nielsen Holdings plc)
• Original Assignee: Nielsen Company (US) LLC (RR Donnelley & Sons Company)
• Inventors: Lee, Michael J., Lee, Hans C.
• Granted Patent: US 8,376,952 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6814 Head

Abstract

An exemplary embodiment providing one or more improvements includes a blood oxygen sensing apparatus and method in which an infra-red light is absorbed blood in portions that are related to levels of oxygen in the blood along a path.

Claims

1. A method for determining at least one circulatory related characteristic of a person, comprising:

generating an oscillating light having an intensity that oscillates at an oscillating light frequency, the oscillating light including an electromagnetic wavelength which causes the oscillating light to be absorbed by some tissue of the person in amounts that are proportional to a volume of oxygenated blood in the tissue of the person;

directing the oscillating light towards the tissue of the person to cause the oscillating light to enter the tissue and pass through the tissue along a light path from which a first portion of the oscillating light exits the tissue and along which a second portion of the oscillating light is absorbed by the oxygenated blood in the light path such that the first portion is modulated by a volume of oxygenated blood that is present in said light path;

detecting levels of light near the tissue and creating a detector signal which is related to the detected light levels, the detected light including at least some of the first portion of the oscillating light exiting from the tissue and a secondary light from other sources, the detector signal including a first component caused by detection of the first portion of the oscillating light exiting the tissue, and a second component caused by the detection of the secondary light;

filtering the detector signal to attenuate at least a part of the second component of the detector signal and to pass the first component of the detector signal substantially un-attenuated; and

determining at least said circulatory characteristic based on a volume of oxygenated blood in the light path through the tissue as characterized by the modulation of the first component of the detector signal.

2. A method as defined in claim 1, further comprising guiding the oscillating light to cause the oscillating light to enter and exit the tissue a plurality of times along the light path before the levels of light are detected near the tissue.

3. A method as defined in claim 2 wherein guiding the oscillating light includes reflecting the oscillating light with a reflective surface.

4. A method as defined in claim 1 wherein the oscillating light is directed to reflect off bone of the person before exiting the tissue.

5. A method as defined in claim 4 wherein the oscillating light is directed to reflect off skull bone of the person before exiting the tissue.

6. A method as defined in claim 1 wherein the characteristic is determined based on an inverse relationship between the first portion of oscillating light exiting the tissue and the second portion of the oscillating light absorbed by the oxygenated blood.

7. A method as defined in claim 1, further comprising blocking exterior light from entering the light path through the tissue.

8. A method as defined in claim 7, further comprising blocking the exterior light by conforming a flexible at least partially opaque material to the tissue.

9. A method as defined in claim 1 wherein the oscillating light is generated at a substantially constant wavelength.

10. A method as defined in claim 9 wherein the oscillating light is generated at a wavelength of about 850 nm.

11. A method as defined in claim 1 wherein the light is oscillated at a frequency above 120 Hz.

12. A method as defined in claim 11 wherein the light is oscillated at about 3.2 kH.

13. A method as defined in claim 1 wherein generating the oscillating light includes turning a light source on and off.

14. A method as defined in claim 1 wherein the detector signal is created with a linear relationship to the detected light levels.

15. A method as defined in claim 14, further comprising generating a bias light and detecting the level of bias light as at least a portion of the secondary light to cause the detector signal to have a linear relationship to the detected light levels.

16. A method as defined in claim 15 wherein the bias light is generated to cause the level of the secondary light to be at a predetermined level.

17. A method as defined in claim 1 wherein the characteristic determined is a breathing rate of the person.

18. A method as defined in claim 1 wherein the characteristic determined is a heart rate of the person.

19. A method as defined in claim 1, further comprising:

asymmetrically amplifying the first component of the detector signal to extend a range of detector signals which are usable for determining the characteristics of the person.

20. A method as defined in claim 19 wherein positive portions of the first component of the detector signal are amplified about four times as much as negative portions of the first component of the detector signal.

21. A blood oxygen sensor for determining at least one circulatory related characteristic of a person, comprising:

an oscillating light generator for generating an oscillating light having an intensity that oscillates at an oscillating light frequency, the oscillating light including an electromagnetic wavelength which causes the oscillating light to be absorbed by some tissue of the person in amounts that are proportional to a volume of oxygenated blood in the tissue toward which the oscillating light is directed;

a light directing apparatus for directing the oscillating light toward the tissue of the person to cause the oscillating light to enter the tissue and pass through the tissue along a light path from which a first portion of the oscillating light exits the tissue and along which a second portion of the light is absorbed by the oxygenated blood in the light path such that the first portion is modulated by a volume of oxygenated blood that is present in said light path;

a light detector for detecting levels of light near the tissue in a spaced apart relationship to the light directing apparatus, and for creating a detector signal which is related to the detected light levels, the detected light including at least some of the first portion of the oscillating light exiting from the tissue and a secondary light from sources other than the oscillating light generator, the detector signal including a first component caused by detection of the first portion of the oscillating light exiting the tissue, and a second component caused by the detection of the secondary light;

a filter for filtering the detector signal to attenuate at least part of the second component of the detector signal and to pass the first component of the detector signal substantially un-attenuated; and

a computing device for receiving the filtered detector signal and for determining at least said circulatory characteristics relating to the person based on a volume of oxygenated blood in the light path through the tissue as characterized by the modulation of the first component of the detector signal.

22. A blood oxygen sensor as defined in claim 21, further comprising:

a light guide for returning oscillating light exiting from the tissue back into the tissue at a position between the light directing apparatus and the light detector, the oscillating light thereafter exiting the tissue at a position where the light detector detects the levels of the first portion oscillating light and the secondary light.

23. A blood oxygen sensor as defined in claim 22 wherein the light guide includes a reflective surface for returning oscillating light back into the tissue.

24. A blood oxygen sensor as defined in claim 22 wherein the light guide includes an opaque portion to reduce secondary light at the light detector.

25. A blood oxygen sensor as defined in claim 21 wherein the computing device determines the characteristic based on an inverse relationship between the first portion of oscillating light exiting the tissue and the second portion of the oscillating light absorbed by the oxygenated blood.

26. A blood oxygen sensor as defined in claim 21 wherein the oscillating light generator generates the oscillating light at a substantially constant wavelength.

27. A blood oxygen sensor as defined in claim 26 wherein the oscillating light generator generates the oscillating light at a wavelength of about 850 nm.

28. A blood oxygen sensor as defined in claim 21 wherein the oscillating light generator oscillates the light at a frequency above 120 Hz.

29. A blood oxygen sensor as defined in claim 28 wherein the oscillating light generator oscillates the light at a frequency of about 3.2 kH.

30. A blood oxygen sensor as defined in claim 21 wherein the oscillating light generator oscillates the light by turning a light source on and off.

31. A blood oxygen sensor as defined in claim 21 wherein the light detector operates in a linear range when detecting levels of light.

32. A blood oxygen sensor as defined in claim 31 further comprising:

a bias light source positioned to supply a bias light to the light detector, and wherein the secondary light includes external light from at least one source that is not associated with the blood oxygen sensor and the bias light from the bias light source and the bias light is supplied by the bias light source at a level which causes the secondary light to be at a predetermined level to bias the light detector in the linear range.

33. A blood oxygen sensor as defined in claim 21 wherein the computing device determines a breathing rate from the filtered detector signal.

34. A blood oxygen sensor as defined in claim 21 wherein the computing device determines a heart rate from the filtered detector signal.

35. A blood oxygen sensor as defined in claim 34, further comprising:

an asymmetric amplifier for asymmetrically amplifying the first component of the detector signal to extend a range of detector signals which are usable for determining the heart rate.

36. A blood oxygen sensor as defined in claim 35 wherein the amplifier is configured to amplify positive portions of the first component of the detector signal about four times as much as negative portions of the first component of the detector signal.

37. A blood oxygen sensor as defined in claim 21 wherein at least part of the filter is accomplished by the computing device.

38. A method for determining at least one circulatory related characteristic of a person, comprising:

generating light at a wavelength which causes the light to be absorbed by some tissue of the person in amounts that are proportional to a volume of oxygenated blood in the tissue towards which the light is directed;

directing the light towards the tissue of the person to cause the light to enter the tissue;

guiding the light to cause to light to pass through the tissue along a light path which includes the light entering and exiting the tissue a plurality of times, a first portion of the light exiting the tissue and a second portion of the light is absorbed by the oxygenated blood in the light path such that the first portion is modulated by a volume of oxygenated blood that is present in said light path;

detecting levels of light near the tissue after the light has passed through the light path and creating a detector signal which is related to the detected light levels, the detected light including at least some of the first portion of light exiting from the tissue and a secondary light from other sources, the detector signal including a first component caused by detection of a first portion of light exiting the tissue, and a second component caused by the detection of the secondary light; and

determining at least said circulatory characteristic based on a volume of oxygenated blood in the light path through the tissue as characterized by the modulation of the first component of the detector signal.

39. A method as defined in claim 38 wherein the light is guided to reflect off of bone of the person in at least one portion of the light path through the tissue.

40. A method as defined in claim 39 wherein the light is guided to reflect off of the skull bone of the person.

41. A method as defined in claim 38 wherein the light is guided to reflect off of the skull bone of the person a plurality of times before the levels of light are detected.

42. A method as defined in claim 38, further comprising:

generating a bias light, and wherein detecting levels of light includes detecting the bias light as at least a portion of the second component to cause the levels of light detected to be at an approximately constant average level.

43. A method as defined in claim 38 wherein the light is generated to have an oscillatory characteristic.

44. A method as defined in claim 38 wherein the detector signal is amplified asymmetrically.

45. A blood oxygen sensor for determining at least one circulatory related characteristic of a person, comprising:

a light generator for generating a light at a wavelength which causes the light to be absorbed by some tissue of the person in amounts that are proportional to a volume of oxygenated blood in the tissue toward which the light is directed;

a light directing apparatus for directing the light toward the tissue of the person to cause the light to enter the tissue;

a light guide for guiding the light to pass through the tissue along a light path which includes the light entering and exiting the tissue a plurality of times, a first portion of the light exiting the tissue and a second portion of the light is absorbed by the oxygenated blood in the light path such that the first portion is modulated by a volume of oxygenated blood that is present in said light path;

a light detector for detecting levels of light near the light guide which includes at least some of the first portion of light exiting from the tissue and for creating a detector signal which is related to the detected light levels; and

a computing device for receiving the detector signal and for determining at least said circulatory characteristic based on a volume of oxygenated blood in the light path through the tissue as characterized by the modulation of the first portion of the light exiting the tissue.

46. A blood oxygen sensor as defined in claim 45 wherein the light guide is arranged to reflect light exiting the tissue back into the tissue at least once.

47. A blood oxygen sensor as defined in claim 45 wherein the light directing apparatus directs the light toward tissue of the person in a location which causes the light to reflect off of bone of the person.

48. A blood oxygen sensor as defined in claim 47 wherein the light is directed at a location which causes the light to reflect off of the skull bone of the person.

49. A blood oxygen sensor as defined in claim 45, further comprising:

a bias light source positioned to supply a bias light to the light detector to bias the detector into a linear range.

50. A blood oxygen sensor as defined in claim 49 wherein the light guide is arranged to reflect light exiting the tissue back into the tissue at least once.

51. A blood oxygen sensor as defined in claim 45 further comprising:

a flexible light blocking apparatus for conforming to the tissue of the person and at least partially blocking light that is not generated by the blood oxygen sensor from reaching the light detector.

52. A blood oxygen sensor as defined in claim 45 wherein the detector signal is amplified asymmetrically.