Method for spectrophotometric blood oxygenation monitoring

• US 20060189861A1
• Filed: 03/16/2006
• Published: 08/24/2006
• Est. Priority Date: 07/26/2002
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Chen, Bo, Benni, Paul B.
• Granted Patent: US 8,078,250 B2
• Time in Patent Office: Days
• US Class Current: 600/331
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue

Abstract

A method and apparatus for non-invasively determining the blood oxygenation within a subject'"'"'s tissue is provided that utilizes a near infrared spectrophotometric (NIRS) sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal once it has passed through the tissue via transmittance or reflectance.

Claims

1. A method for determining blood oxygenation within a subject'"'"'s tissue, said:

method comprising the steps;

transmitting a light signal with a near infrared spectrophotometric sensor along a plurality of wavelengths into the subject'"'"'s tissue;

receiving light energy with the sensor corresponding to the light signal after the light signal has passed through the subject'"'"'s tissue;

processing the light energy received along the plurality of wavelengths, including using wavelength dependent sensor calibration constants representative of energy losses incurred by the light signal passing through the subject'"'"'s tissue, to determine the blood oxygenation within the subject'"'"'s tissue.

2. The method of claim 1, wherein the processing includes the determination of the blood oxygen saturation level within the subject'"'"'s tissue.

3. The method of claim 1, wherein the processing step includes determining the wavelength dependent sensor calibration constants.

4. The method of claim 3, wherein the step of determining the wavelength dependent sensor calibration constants includes the use of empirical data or a reference sample.

5. The method of claim 1, wherein the energy losses are attributable to one or more of light scattering, absorption from background biological compounds, and apparatus variability.

6. The method of claim 1, wherein the calibration constants are operable to calibrate the sensor for use on a plurality of different subjects without recalibration.

7. The method of claim 1, wherein the processing step includes determining one or both of oxyhemoglobin concentration and deoxyhemoglobin concentration within the subject'"'"'s tissue.

8. The method of claim 7, wherein the concentrations of one or both of oxyhemoglobin and deoxyhemoglobin are determined by determining values of oxyhemoglobin and deoxyhemoglobin at a first point in time, and the changes in oxyhemoglobin and deoxyhemoglobin at a second point in time later than the first point in time.

9. The method of claim 1, further comprising the step of determining the arterial oxygen saturation within the subject using a pulse oximeter, and processing the arterial oxygen saturation with the light energy received along the plurality of wavelengths, to determine the venous blood oxygen saturation level within the subject'"'"'s tissue.

10. A method for determining blood oxygenation within a subject'"'"'s tissue, said method comprising the steps:

transmitting a light signal with a near infrared spectrophotometric sensor along at least three wavelengths into the subject'"'"'s tissue;

receiving light energy with the sensor corresponding to the light signal after the light signal has passed through the subject'"'"'s tissue;

processing the light energy received along each of the at least three wavelengths, including compensating for energy losses attributable to absorption from biological compounds other than hemoglobin, to determine the blood oxygenation within the subject'"'"'s tissue.

11. The method of claim 10, wherein the processing step includes determining wavelength dependent sensor calibration constants.

12. The method of claim 11, wherein the step of determining wavelength dependent sensor calibration constants includes the use of empirical data or a reference sample.

13. The method of claim 10, wherein the energy losses are also attributable to apparatus variability.

14. The method of claim 10, further comprising the step of determining one or both of oxyhemoglobin concentration and deoxyhemoglobin concentration within the subject'"'"'s tissue.

15. The method of claim 10, wherein the processing includes the determination of the blood oxygen saturation level within the subject'"'"'s tissue.

16. A method for determining blood oxygenation within a subject'"'"'s tissue, said method comprising the steps:

transmitting a light signal with a near infrared spectrophotometric sensor along at least a first wavelength, a second wavelength, and a third wavelength, into the subject'"'"'s tissue;

receiving light energy with the sensor corresponding to the light signal after the light signal has passed through the subject'"'"'s tissue;

processing the light energy received along the first, second, and third wavelengths, including determining the difference in attenuation of the light signal between the first wavelength and second wavelength, and between the first wavelength and the third wavelength, and determining wavelength dependent sensor calibration constants to compensate for energy losses, to determine the blood oxygenation within the subject'"'"'s tissue.

17. The method of claim 16, wherein the processing includes the determination of the blood oxygen saturation level within the subject'"'"'s tissue.

18. The method of claim 16, wherein the wavelength dependent calibration constants are subject independent.

19. The method of claim 16, wherein the energy losses are attributable to one or more of light scattering, absorption from biological compounds, and apparatus variability.

20. The method of claim 18, wherein the step of receiving light energy includes receiving light energy with at least one first light signal detector spaced apart from a light signal transmitter by a first distance, and with at least one second light signal detector spaced apart from the light signal transmitter by a second distance, wherein the second distance is greater than the first distance.

21. The device of claim 20, wherein the step of processing the light energy received includes contrasting a signal detected at the first signal detector from a signal detected at the second light signal detectors for each discrete wavelength.

22. The method of claim 16, further comprising the step of determining one or both of an oxyhemoglobin concentration and a deoxyhemoglobin concentration within the subject'"'"'s tissue.

23. The method of claim 16, further comprising the step of determining an arterial oxygen saturation within the subject'"'"'s tissue using a pulse oximeter.

24. The method of claim 23, further comprising the step of determining a venous oxygen saturation within the subject'"'"'s tissue using the arterial oxygen saturation determined using the pulse oximeter.

25. A spectrophotometric examination device, comprising:

a light signal transmitter operable to transmit at least one light signal along a plurality of discrete wavelengths;

at least one light signal detector operable to detect the light signal, and produce at least one detected signal corresponding to the light signal; and

a processor having an algorithm for determining the blood oxygenation in a subject'"'"'s tissue, the algorithm being operable to process the detected signal along a plurality of discrete wavelengths, and the algorithm including a plurality of wavelength dependent calibration constants to compensate for energy losses incurred by the light signal passing through the subject'"'"'s tissue.

26. The device of claim 25, wherein the algorithm is operable to determine the blood oxygen saturation level within the subject'"'"'s tissue.

27. The device of claim 25, wherein the light signal transmitter is operable to transmit the light signal along at least three discrete wavelengths.

28. The device of claim 25, wherein the wavelength dependent calibration constants are subject independent.

29. The device of claim 25, wherein the energy losses are attributable at least in part to one or more of light scattering, absorption from biological compounds, and apparatus variability.

30. The device of claim 25, wherein the at least one light signal detector operable to detect the light signal, includes a first light signal detector spaced apart from the light signal transmitter by a first distance, and a second light signal detector spaced apart from the light signal transmitter by a second distance, wherein the second distance is greater than the first distance.

31. The device of claim 25, wherein the algorithm is operable to process the detected signal along each discrete wavelength, by contrasting a signal detected at the first signal detector from a signal detected at the second light signal detectors for each discrete wavelength.

32. The device of claim 25, wherein the algorithm is operable to determine the total concentration of one or both of oxyhemoglobin and deoxyhemoglobin.

33. The device of claim 25, further comprising a pulse oximeter operable to determine arterial oxygen saturation within the subject.

34. The device of claim 25, wherein the algorithm is operable to determine a venous oxygen saturation within the subject'"'"'s tissue using the arterial oxygen saturation determined using the pulse oximeter.

35. The device of claim 25, wherein the wavelength dependent calibration constants are based on empirical data or a reference sample.

36. The device of claim 25, wherein the energy losses are selected from a group consisting of absorption from background biological compounds, and apparatus variability.

37. The device of claim 25, wherein the calibration constants are operable to calibrate the device for use on a plurality of different subjects without recalibration.

38. A spectrophotometric examination device, comprising:

a light signal transmitter operable to transmit at least one light signal along at least three discrete wavelengths;

at least one light signal detector operable to detect the light signal, and produce at least one detected signal corresponding to the light signal; and

a processor having an algorithm for determining the blood oxygenation in a subject'"'"'s tissue, the algorithm being operable to process the light energy received along a plurality of wavelengths, and compensate for energy losses attributable to absorption from biological compounds other than hemoglobin, to determine the blood oxygenation within the subject'"'"'s tissue.

39. The device of claim 38, wherein the algorithm is operable to determine the blood oxygen saturation level within the subject'"'"'s tissue.

40. The device of claim 38, wherein the energy losses are at least partially attributable to one or more of light scattering, absorption from background biological compounds, and apparatus variability.

41. The device of claim 38, wherein the algorithm is operable to calibrate the device for use on a plurality of different subjects without recalibration.