Pathlength Enhancement of Optical Measurement of Physiological Blood Parameters

• US 20130331710A1
• Filed: 06/12/2012
• Published: 12/12/2013
• Est. Priority Date: 06/12/2012
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Li, Youzhi, Baker, Clark R. Jr.
• Granted Patent: US 9,050,044 B2
• Time in Patent Office: Days
• US Class Current: 600/479
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 2562/0242 for varying or adjusting the optical path length in the tissue
• CPC Class Codes: A61B 2576/00 Medical imaging apparatus involving image processing or analysis A61B1/00009, A61B6/52 and A61B8/52 take precedence; image processing per se G06T; details of algorithms for analysing medical images G06T7/0012
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6803 Head-worn items, e.g. helmets, masks, headphones or goggles
• CPC Class Codes: A61B 5/6844 Monitoring or controlling distance between sensor and tissue
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7246 using correlation, e.g. template matching or determination of similarity
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Systems and methods for measuring a physiological parameter of tissue in a patient are provided herein. In a first example, a method of measuring a physiological parameter of blood in a patient is provided. The method includes emitting at least two optical signals for propagation through tissue of the patient, detecting the optical signals after propagation, identifying propagation pathlengths of the optical signals, and identifying detected intensities of the optical signals. The method also includes processing at least the propagation pathlengths to scale the detected intensities for determination of a value of the physiological parameter.

Claims

1. A method of measuring a physiological parameter of blood in a patient, the method comprising:

emitting at least two optical signals for propagation through tissue of the patient;

detecting the optical signals after propagation;

identifying propagation pathlengths of the optical signals;

identifying detected intensities of the optical signals; and

processing at least the propagation pathlengths to scale the detected intensities for determination of a value of the physiological parameter.

2. The method of claim 1, wherein emitting the at least two optical signals comprises emitting a first optical signal and a second optical signal at a first location of the tissue;

wherein detecting the optical signals after propagation comprises detecting the first optical signal at a second location of the tissue and detecting the second optical signal at a third location of the tissue different than the second location;

wherein processing at least the propagation pathlengths to scale the detected intensities comprises processing a first carrier wavelength of the first optical signal and a second carrier wavelength of the second optical signal, distances between the first location and each of the second location and the third location, and the propagation pathlengths of the first optical signal and the second optical signal to scale the detected intensities.

3. The method of claim 1, wherein processing at least the propagation pathlengths to scale the detected intensities comprises scaling a ratio of the intensities of the at least two optical signals with a ratio of the propagation pathlengths of the at least two optical signals.

4. The method of claim 1, wherein identifying the propagation pathlengths of the optical signals comprises determining a phase delay and processing the phase delay with a propagation speed through the tissue for at least one of the optical signals.

5. The method of claim 1, further comprising:

comparing at least one of the propagation pathlengths to a propagation pathlength range to determine an invalid application of a tissue interface assembly employed to emit the optical signals for propagation through the tissue.

6. The method of claim 1, wherein the physiological parameter comprises at least one of a total hemoglobin concentration (tHb) parameter, regional oxygen saturation (rSO2) parameter, and arterial oxygen saturation (SpO2) parameter of the blood of the patient.

7. A method of operating a system for measuring a physiological parameter of blood in a patient, the method comprising:

emitting at least one optical signal for propagation into tissue of the patient via a tissue interface assembly;

receiving the at least one optical signal after propagation;

identifying a propagation pathlength of the at least one optical signal; and

processing at least the propagation pathlength to determine a state of the tissue interface assembly on the tissue.

8. The method of claim 7, wherein processing at least the propagation pathlength to determine the state of the tissue interface assembly on the tissue comprises comparing the propagation pathlength of the at least one optical signal to a pathlength range to determine an invalid application of the tissue interface assembly.

9. The method of claim 8, wherein the invalid application of the tissue interface assembly comprises a gap between the tissue and the tissue interface assembly.

10. The method of claim 8, wherein the invalid application of the tissue interface assembly comprises an application of the tissue interface assembly onto tissue perfused by blood below a perfusion threshold.

11. The method of claim 7, wherein identifying the propagation pathlength of the at least one optical signal comprises determining a phase delay of the at least one optical signal and processing the phase delay with a propagation speed through the tissue for the at least one optical signal.

12. The method of claim 7, wherein emitting the at least one optical signal for propagation into tissue of the patient via the tissue interface assembly comprises emitting the at least one optical signal through at least a gap between the tissue interface assembly and the tissue;

and

wherein processing at least the propagation pathlength to determine the state of the tissue interface assembly on the tissue comprises determining the state of the tissue interface assembly as including the gap between the tissue interface assembly and the tissue.

13. The method of claim 7, wherein receiving the at least one optical signal after propagation comprises receiving the at least one optical signal after propagation through at least a gap between the tissue interface assembly and the tissue;

and

wherein processing at least the propagation pathlength to determine the state of the tissue interface assembly on the tissue comprises determining the state of the tissue interface assembly as including the gap between the tissue interface assembly and the tissue.

14. The method of claim 7, further comprising:

processing at least the propagation pathlength of the at least one optical signal and a detected intensity of the at least one optical signal to determine of a value of the physiological parameter when the state of the tissue interface assembly on the tissue indicates a proper application of the tissue interface assembly.

15. A system for measuring a physiological parameter of blood in a patient, comprising:

a tissue interface assembly configured to emit at least one optical signal for propagation into tissue of the patient and receive the at least one optical signal after propagation; and

a measurement system configured to identify a propagation pathlength of the at least one optical signal, and process at least the propagation pathlength to determine a state of the tissue interface assembly on the tissue.

16. The system of claim 15, wherein the measurement system is configured to compare the propagation pathlength of the at least one optical signal to a pathlength range to determine an invalid application of the tissue interface assembly as the state of the tissue interface assembly on the tissue.

17. The system of claim 16, wherein the invalid application of the tissue interface assembly comprises a gap between the tissue and the tissue interface assembly.

18. The system of claim 15, wherein the tissue interface assembly is configured to emit the at least one optical signal through at least a gap between the tissue interface assembly and the tissue, and wherein the measurement system is configured to process at least the propagation pathlength to determine the state of the tissue interface assembly on the tissue as including the gap between the tissue interface assembly and the tissue.

19. The system of claim 15, wherein the tissue interface assembly is configured to receive the at least one optical signal after propagation through at least a gap between the tissue interface assembly and the tissue, and wherein the measurement system is configured to process at least the propagation pathlength to determine the state of the tissue interface assembly on the tissue as including the gap between the tissue interface assembly and the tissue.

20. The system of claim 15, wherein the measurement system is configured to process at least the propagation pathlength of the at least one optical signal and a detected intensity of the at least one optical signal to determine of a value of the physiological parameter when the state of the tissue interface assembly on the tissue indicates a proper application of the tissue interface assembly.