Method and Apparatus for Determining One or More Blood Parameters From Analog Electrical Signals

• US 20100286497A1
• Filed: 05/05/2010
• Published: 11/11/2010
• Est. Priority Date: 05/06/2009
• Status: Active Grant

• Current Assignee: Elfi-Tech Ltd
• Original Assignee: Elfi-Tech Ltd
• Inventors: Kaminsky, Alexander, Fine, Ilya
• Granted Patent: US 8,708,907 B2
• Time in Patent Office: Days
• US Class Current: 600/369
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/02241 of small dimensions, e.g. adapted to fingers
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

Embodiments of the present invention relate to a system and method for in vivo measurement of blood parameters by processing analog electrical signals from a plurality of photodetectors. In some embodiments, it is possible to determine one or more blood parameters according to (i) a first electrical signal from a first detector and (ii) a second electrical signal from a second photodetector. A difference analog electrical signal is generated, indicative of a difference between the light response signal at the first location and light response signal at the second location, is generated. One or more blood parameters may be detected according to the difference analog electrical signal.

Claims

1. ) An apparatus for obtaining physiological information from a subject the apparatus comprising:

a) one or more light sources configured to apply partially or entirely coherent light to a target region of the subject to induce a light response signal from the illuminated target region;

b) a detection system including;

i) a first photodetector configured to detect the light response signal prevailing at a first location to generate a first photodetector analog electrical signal; and

ii) a second photodetector configured to detect the second light response signal prevailing at a second location to generate a second photodetector analog electrical signal, the second location being offset from the first location by an offset distance that is at least 0 5 mm and at most 2 cm;

c) an analog electronics assembly configured to generate, from the first and second analog electrical signals, a difference analog electrical signal that is indicative of a difference between the light response signal at the first location and light response signal at the second location;

d) a digitizer for digitizing the difference analog electrical signal to generate a digitized signal; and

e) a digital processing unit operative to receive and analyze the digitized signal to compute at least one physiological parameter of the subject.

2. ) The apparatus of claim 1 further comprising:

g) a pressurizing assembly operative to induce a change in blood flow at or near the target region by applying a pressure or a force to the subject'"'"'s skin.

3. ) The apparatus of claim 2 wherein the pressurizing assembly includes:

i) a strap for constricting blood flow in a subject'"'"'s finger; and

ii) a pneumatic tube for tightening the strap around the subject'"'"'s finger to constrict the blood flow.

4. ) The apparatus of claim 3 wherein the pressurizing assembly is operative to create an intermittent blood stasis state by applying over systolic blood pressure to the subject, thereby enabling determination of red blood cell (RBC) aggregation.

5. ) The apparatus of claim 1 wherein the digital processing unit is configured:

(i) to detect stochastic time-dependent fluctuations in a magnitude of the difference analog electrical signal; and

(ii) to compute the at least one physiological parameters in accordance with the detected stochastic fluctuations.

6. ) The apparatus of claim 1 wherein the digital processing unit is operative to compute a blood velocity parameter from the digitized signal.

7. ) The apparatus of claim 1 wherein the digital processing unit is operative to compute a blood rheology parameter from the digitized signal.

8. ) The apparatus of claim 1 wherein the digital processing unit is operative to compute from the digitized signal at least one parameter selected from the group consisting of a blood viscosity, a blood particle size and a blood coagulation rate.

9. ) The apparatus of claim 1 wherein the first photodetector is situated at the first location and the second photodetector is situated at the second location, and a distance between the first and second detectors is the offset distance.

10. ) The apparatus of claim 1 wherein the first and/or second photodetectors are respectively situated away from the first and second locations and respectively receive light respectively from the first and/or second location via an optical fiber.

11. ) The apparatus of claim 1 wherein the digital processing unit is operative to effect at least one of

(i) a temporal autocorrelation analysis of the digitized signal;

(ii) effecting a power spectrum analysis of the digitized signal;

and wherein the at least one physiological parameter is computed in accordance with results of the temporal autocorrelation and/or power spectrum analysis.

12. ) The apparatus of claim 1 wherein:

i) is configured to receive;

A) a first input analog signal derived from the first analog photodetector analog electrical signal; and

B) a second input analog signal derived from the second analog photodetector analog electrical signal; and

ii) to generate the difference analog electrical signal from a difference between the first and second input signals.

13. ) A method for obtaining physiological information from a subject in accordance with a light field whose intensity varies according to location, the method comprising:

a) applying partially or entirely coherent light to a target region of the subject to induce a light response signal from the illuminated target region which contributes to a location-dependent light field;

b) detecting the light field prevailing at a first location to generate a first analog signal, the first analog signal including a DLS component of is indicative of a first dynamic light scattering (DLS) measurement;

c) detecting the light field signal prevailing at a second location to generate a second analog signal including a DLS component that is indicative of a second dynamic light scattering (DLS) measurement a ratio and that is uncorrelated with the DLS component of the first analog signal; and

d) processing the first and second analog signals to generate a processed analog signal including a DLS component that is indicative of a combination of the first and second dynamic scattering measurements,

wherein the method is carried out so that a ratio between;

i) a boosted DLS contribution ratio between a magnitude of the DLS component of the processed analog signal and the magnitude of the processed analog signal; and

ii) at least one of a first DLS contribution ratio and a second DLS contribution ratio,

is at least 10, and wherein;

i) the first DLS contribution ratio is defined as a ratio between a magnitude of the DLS component of the first analog signal and the magnitude of the first analog signal; and

ii) the second output ratio is defined as a ratio between a magnitude of the DLS component of the second analog signal and the magnitude of the second analog signal.

14. ) The method of claim 13 further comprising:

e) digitizing the processed analog signal to generate a digital signal indicative of a combination of the first and second dynamic scattering measurements;

f) processing the indicative digital signal to compute at least one physiological parameter.

15. ) The method of claim 14 wherein the computing includes computing at least one of a blood velocity, a blood rheological parameter, a blood pressure, a heartbeat, a blood oxygen concentration, a pulse,

16. ) The method of claim 13 further comprising:

e) before the light field detecting, inducing a change in blood flow at or near the target region.

17. ) The method of claim 16 wherein the blood flow change inducing is carried out by applying a force or a pressure to the subject.

18. ) The method of claim 17 wherein the target region is located in a location selected from the group consisting of a finger region, a back region, a leg region, a face region and an arm region.

19. ) The method of claim 17 wherein the method is carried out so that the first output ratio and/or the second output ratio is at most 0.05

20. ) The method of claim 13 wherein method is carried out such that an ambient light component of the detected light field signal prevailing at the first location is substantially equal to an ambient light component of the detected light field signal prevailing at the second location.

21. ) The method of claim 13 wherein method is carried out such that a slowly-varying component of the detected light field signal prevailing at the first location is substantially equal to an slowly-varying component of the detected light field signal prevailing at the second location.

22. ) The method of claim 13 wherein method is carried out such that a rapidly-varying non-stochastic rapidly-varying component of the detected light field signal prevailing at the first location is substantially equal to a non-stochastic rapidly-varying component of the detected light field signal prevailing at the second location.

23. ) The method of claim 13 wherein a ratio between an intensity, at a wavelength of the at least partially coherent light, of the detected light field signal prevailing at the first location and intensity, at a wavelength of the at least partially coherent light, of the detected light field signal prevailing at the second location is between 0.95 and 1.05.