METHOD FOR SPECTROPHOTOMETRIC BLOOD OXYGENATION MONITORING

• US 20090281403A1
• Filed: 05/10/2006
• Published: 11/12/2009
• Est. Priority Date: 05/12/2005
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Benni, Paul
• Granted Patent: US 8,396,526 B2
• Time in Patent Office: Days
• US Class Current: 600/331
• 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: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/6814 Head
• CPC Class Codes: G01N 2021/3144 for oxymetry
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/49 within a body or fluid

Abstract

According to the present invention, a method and apparatus for non-invasively determining the blood oxygen saturation level within a subject'"'"'s tissue is provided. The method comprises the steps of: 1) providing a near infrared spectrophotometric sensor operable to transmit light along a plurality of wavelengths into the subject'"'"'s tissue; 2) sensing the light transmitted into the subject'"'"'s tissue using the sensor, and producing signal data representative of the light sensed from the subject'"'"'s tissue; 3) processing the signal data to account for physical characteristics of the subject; and 4) determining the blood oxygen saturation level within the subject'"'"'s tissue using a difference in attenuation between the wavelengths. The apparatus includes a sensor having a light source and at least one light detector, which sensor is operably connected to a processor. The sensor is operable to transmit light along a plurality of wavelengths into the subject'"'"'s tissue, and produce signal data representative of the light sensed from the subject'"'"'s tissue. The algorithm is operable to process the signal data to account for the physical characteristics of the subject being sensed.

Claims

1. A method for non-invasively determining a blood oxygen saturation level of the microvasculature within a subject'"'"'s tissue, comprising the steps of:

providing a spectrophotometric sensor operable to transmit light into the subject'"'"'s tissue, and to sense the light;

detecting light after passage through the subject'"'"'s tissue using the sensor, and producing signal data from the light sensed;

processing the signal data, including the steps of cancelling out wavelength independent background light absorption and scattering from a difference in attenuation between select wavelengths, and accounting for wavelength dependent optical characteristics of the subject'"'"'s tissue using the signal data; and

determining the blood oxygen saturation level within the subiject'"'"'s tissue compensating for wavelength dependent physical characteristics of the subject'"'"'s tissue.

2. The method of claim 1, wherein the physical characteristics of the subject'"'"'s tissue include pigmentation of skin and tissue disposed below the skin.

3. The method of claim 2, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

4. The method of claim 3, wherein the processing determines one or more calibration constants using the absorption coefficients for pigmentation, which calibration constants are used to within the step of determining the blood oxygen saturation level within the subject'"'"'s tissue.

5. A method for non-invasively determining a blood oxygen saturation level of the microcirculation within a subject'"'"'s tissue using a spectrophotometric sensor operable to transmit light into the subject'"'"'s tissue, and to sense the light, the method comprising the steps of:

sensing the subject'"'"'s tissue using the sensor, and producing signal data there from, which signal data is attributable to non-pulsatile blood flow within the microcirculation of the subject'"'"'s tissue;

processing the signal data, including the steps of cancelling out wavelength independent background light absorption and scattering from a difference in attenuation between select wavelengths, and accounting for wavelength dependent optical characteristics of the subject'"'"'s tissue using the signal data; and

determining the blood oxygen saturation level within the subject'"'"'s tissue compensating for wavelength dependent physical characteristics of the subject'"'"'s tissue.

6. The method of claim 5, wherein the physical characteristics of the subject'"'"'s tissue comprise pigmentation of skin and tissue disposed below the skin.

7. The method of claim 6, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

8. A method for non-invasively determining a blood oxygen saturation level of the microcirculation within a subject'"'"'s tissue using a spectrophotometric sensor, said method comprising the steps of:

transmitting light into the subject'"'"'s tissue using the sensor;

sensing the light using the sensor, wherein the light is sensed along a plurality of selectively chosen wavelengths, after the light travels through the subject'"'"'s tissue, and producing signal data from sensing the subject'"'"'s tissue;

processing the signal data, including the steps of cancelling out wavelength independent background light absorption and scattering from the difference in attenuation between select wavelengths, accounting for wavelength dependent optical characteristics of the particular subject'"'"'s tissue, and creating one or more calibration constants to account for the subject'"'"'s wavelength dependent tissue optical properties; and

determining the blood oxygen saturation level within the subject'"'"'s tissue using a difference in attenuation using a subset of the chosen plurality of wavelengths and the calibration constants.

9. The method of claim 8, wherein the step of determining the blood oxygen saturation level within the subject'"'"'s tissue comprises processing signal data other than that used to create the one or more calibration constants.

10. The method of claim 9, wherein the blood oxygen saturation level within the subject'"'"'s tissue is determined using a difference in attenuation between a first of the wavelengths and each of the other of the wavelengths.

11. The method of claim 10, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

12. The method of claim 8, wherein the blood oxygen saturation level within the subject'"'"'s tissue is determined using a difference in attenuation between a first of the wavelengths and each of the other of the wavelengths.

13. The method of claim 8, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

14. A method for calibrating a NIRS sensor, comprising the steps of:

transmitting light into a subject'"'"'s tissue using the sensor;

sensing the light using the sensor, along a plurality of selectively chosen wavelengths after the light travels through the subject'"'"'s tissue, and producing signal data from sensing the subject'"'"'s tissue; and

calibrating the sensor using the signal data.

15. The method of claim 14, wherein the calibrating step includes processing the signal data to consider pigmentation of the subject'"'"'s tissue.

16. The method of claim 15, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

17. A method for non-invasively determining a blood oxygen saturation level of the microcirculation within a subject'"'"'s tissue, comprising the steps of:

providing a spectrophotometric sensor operable to transmit light into the subject'"'"'s tissue, and to sense the light;

sensing the subject'"'"'s tissue using the sensor, and producing signal data from the sensing, which signal data is attributable to non-pulsatile blood flow within the microcirculation of the subject'"'"'s tissue; and

processing the signal data, including the steps of cancelling out wavelength independent background light absorption and scattering from a difference in attenuation between select wavelengths, accounting for wavelength dependent optical characteristics of the particular subject'"'"'s tissue, and determining the concentration of oxyhemoglobin, deoxyhemoglobin of the microvasculature, and the blood oxygen saturation level of the microvasculature within the subject'"'"'s tissue.

18. The method of claim 17, wherein the step of processing the signal data comprises initially determining the concentration of oxyhemoglobin, deoxyhemoglobin, and pigmentation within the subject'"'"'s tissue, and subsequently determining the blood oxygen saturation level within the subject'"'"'s tissue using the determined concentrations of oxyhemoglobin and deoxyhemoglobin.

19. The method of claim 18, wherein the step of processing the signal data comprises using the determined pigmentation concentration to calibrate the sensor.

20. The method of claim 19, wherein the processing step includes the use of absorption coefficients for pigmentation in the subject'"'"'s tissue.

21. A method for non-invasively determining a blood oxygen saturation level within a subject'"'"'s tissue, comprising the steps of:

providing a spectrophotometric sensor operable to transmit light within a predetermined range of wavelengths into the subject'"'"'s tissue, and to sense a plurality of preselected wavelengths of the light disposed within the range;

sensing the subject'"'"'s tissue using the sensor, and producing signal data from sensing the subject'"'"'s tissue; and

processing the signal data, including determining light attenuation for one or more components of the subject'"'"'s tissue, other than oxyhemoglobin and deoxyhemoglobin, which components have a tissue optical property that varies over the range of wavelengths, to determine the blood oxygenation level within the subject'"'"'s tissue.

22. (canceled)

23. An apparatus for non-invasively determining a blood oxygen saturation level of the microcirculation within a subject'"'"'s tissue, comprising:

at least one spectrophotometric sensor having at least one light source and at least one light detector, wherein the light source is operable to transmit light along a plurality of wavelengths into the subject'"'"'s tissue, and the light detector is operable to detect light from the light source after the light has traveled through the subject'"'"'s tissue, and the sensor is operable to produce signal data attributable to non-pulsatile blood flow within the microcirculation of the subject'"'"'s tissue from the detected light; and

a processor operably connected to the at least one sensor, the processor having an algorithm operable to process the signal data to account for the physical characteristics of the subject'"'"'s tissue.

24. The apparatus of claim 23, wherein the physical characteristics of the subject'"'"'s tissue comprise pigmentation.

25. The apparatus of claim 24, wherein the algorithm utilizes absorption coefficients for pigmentation in the subject'"'"'s tissue.

26. The apparatus of claim 25, wherein the algorithm is operable to process the signal data to determine one or more calibration constants using the absorption coefficients for pigmentation, and operable to determine the blood oxygen saturation level within the subject'"'"'s tissue using the calibration constants.

27. The apparatus of claim 26, wherein the algorithm is operable to determine the blood oxygen saturation level within the subject'"'"'s tissue using signal data other than that used to create to the one or more calibration constants.

28. A method for non-invasively determining a blood oxygen saturation level of the microcirculation within a subject'"'"'s tissue, comprising the steps of:

providing a spectrophotometric sensor operable to transmit light into the subject'"'"'s tissue, and to sense the light;

sensing non-pulsatile light passed through microcirculation within the subject'"'"'s tissue using the sensor, and producing signal data from the sensed non-pulsatile light;

processing the signal data, including the steps of;

cancelling out wavelength independent background light absorption and scattering from a difference in attenuation between select wavelengths, accounting for wavelength dependent optical characteristics of the particular subject'"'"'s tissue being sensed within the sensor, creating one or more calibration constants to account for the subject'"'"'s wavelength dependent tissue optical properties, and determining the concentration of oxyhemoglobin and deoxyhemoglobin of the microvasculature and the blood oxygen saturation level within the subject'"'"'s tissue using a difference in attenuation using a subset of said chosen plurality of wavelengths and said calibration constants.