Detecting chemical components from spectroscopic observations

• US 8,292,809 B2
• Filed: 03/27/2009
• Issued: 10/23/2012
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Pav, Steven E
• Primary Examiner(s): Szmal, Brian
• Assistant Examiner(s): Stout, Michael C
• Application Number:
  US12/412,956
• Publication Number:
  US 20090247844A1
• Time in Patent Office: 1,306 Days
• Field of Search: 600/309, 600/322, 600/323
• US Class Current: 600/309
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

Embodiments disclosed herein may include methods and systems capable of estimating the underlying concentrations of chromophores in a sample. The photon scattering and absorption model may be based on Laplace and stable distributions, which may reveal that measurements in diffuse reflectance may follow a Beer-Lambert and Kohlrausch-Williams-Watts (KWW) product. This Beer-Lambert portion of the product may dominate in high absorption sample areas, while the KWW portion of the product may dominate in low absorption sample areas.

Claims

1. A medical device, comprising:

a monitor adapted to receive a physiologic signal from a patient; and

a processor capable of determining physiological characteristics of the patient based at least in part on the physiologic signal by applying a mixed Beer-Lambert/Kohlrausch-Williams-Watts Model (KWW) algorithm for photon diffusion to the physiologic signal.

2. The medical device of claim 1, wherein the processor is capable of determining an absorption rate of a sample area of the patient from the physiologic signal.

3. The medical device of claim 2, wherein the processor is capable of applying a predicted KWW model of diffuse reflectance when the absorption rate is determined to fall below a threshold value.

4. The medical device of claim 1, comprising a memory device capable of storing the threshold value as a value determined by the processor based at least in part upon the physiologic signal.

5. The medical device of claim 2, wherein the processor is capable of storing a predicted Beer-Lambert model of diffuse reflectance when the absorption rate is

determined to be above a threshold value.

6. The medical device of claim 5, comprising a memory device capable of storing the threshold value as a preprogrammed value.

7. The medical device of claim 1, wherein the processor is capable of determining concentrations of chromophores in a sample area of the patient based at least in part upon the mixed Beer-Lambert/KWW algorithm.

8. The medical device of claim 1, comprising a sensor capable of emitting electromagnetic radiation into a tissue sample of the patient, and detecting the scattered and/or reflected light from the tissue sample.

9. The medical device of claim 8, wherein the sensor is capable of generating the physiologic signal corresponding to the scattered and/or reflected light detected, and directing the physiologic signal to the monitor.

10. A method of calculating physiological characteristics of a patient, comprising:

obtaining a physiologic signal from a patient;

calculating physiological characteristics of the patient based at least in part on the physiologic signal by applying a mixed Beer-Lambert/Kohlrausch-Williams-Watts Model (KWW) algorithm for photon diffusion to the physiologic signal.

11. The method of claim 10, comprising determining an absorption rate of a sample of the patient from the physiologic signal.

12. The method of claim 11, comprising applying a predicted KWW model of diffuse reflectance when the absorption rate is determined to fall below a threshold value.

13. The method of claim 12, comprising calculating the threshold value based at least in part upon the physiologic signal.

14. The method of claim 11, comprising applying a predicted Beer-Lambert model of diffuse reflectance when the absorption rate is determined to be above a threshold value.

15. The method of claim 14, comprising storing the threshold value as a preprogrammed value.

16. The method of claim 10, wherein calculating physiological characteristics of a sample comprises utilizing the mixed Beer-Lambert/KWW algorithm to determine concentrations of chromophores in a sample area of the patient.

17. The method of claim 10, wherein obtaining a physiologic signal comprises:

emitting electromagnetic radiation into a tissue sample of the patient;

detecting the scattered and/or reflected light from the tissue sample;

generating the physiologic signal corresponding to the scattered and/or

reflected light detected and

directing the physiologic signal to the monitor.