Circulation monitoring system and method

• US 20090149764A1
• Filed: 12/11/2007
• Published: 06/11/2009
• Est. Priority Date: 02/28/2007
• Status: Active Grant

• Current Assignee: Semler Scientific, Inc.
• Original Assignee: Semler Scientific, Inc.
• Inventors: Semler, Herbert J., McNames, James, Mills, Gary, Benz, Philip
• Granted Patent: US 7,628,760 B2
• Time in Patent Office: Days
• US Class Current: 600/504
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

A lightweight portable probe or transducer containing a transmissive or reflective electro-optical emitter and receptor in the infrared spectrum is fitted on a subject'"'"'s finger or toe. Associated electronics energize and monitor the probe, detect cardio-rhythmic fluctuations therefrom, and process digital data over a prescribed window to produce a non-invasive, qualitative or quantitative measure of the subject'"'"'s circulation. In accordance with one embodiment of the invention, a simple tri-color LED array is used to indicate the subject'"'"'s circulation as being normal, reduced, or borderline.

Claims

1. Circulation monitoring apparatus comprising:

a transducer configured to illuminate and monitor light fluctuations through tissue within an anatomical extremity to produce a signal indicative of the fluctuations, the transducer including a photo emitter for emitting a light signal to illuminate the extremity and a photo receptor for receiving a light signal responsive thereto;

a processor operatively coupled with the transducer, the processor configured to analyze the signal for periodicity and to measure the signal for amplitude;

a comparator operatively coupled with the processor, the comparator configured to compare the measured amplitude of the signal to one or more predefined threshold amplitudes; and

an indicator operatively coupled with the comparator, the indicator configured to indicate a circulation level from the comparator.

2. The apparatus of claim 1, wherein the indicator includes a tri-color light may indicating three levels of comparison.

3. The apparatus of claim 2, wherein the tri-color light array indicates normal, reduced and insignificant circulation in the extremity.

4. The apparatus of claim 1, wherein the transducer operates tranamissively through the extremity.

5. The apparatus of claim 1, wherein the transducer includes an extremity-embracing circumferential expanse.

6. The apparatus of claim 5, wherein the expanse is flexible.

7. The apparatus of claim 1, wherein the transducer operates reflectively from one side of the extremity.

8. The apparatus of claim 1, wherein the transducer includes an adherent one-sided extremity-contacting expanse.

10. The apparatus of claim 2, wherein the processor, the comparator, and the indicator operate digitally, the apparatus further comprising:

an analog-to-digital converter operatively coupled between the transducer and the processor.

11. The apparatus of claim 1, wherein the transducer, the convener, and the processor operate collectively to capture a window of time-based signal amplitude data representing cardiac rhythmic circulation indicia.

12. The apparatus of claim 1 further comprising:

either of a flexible wiring harness or a cable extending between the transducer and the processor.

13. The apparatus of claim 12 further comprising:

a housing at an end of either of the cable or the wiring harness opposite the transducer, the housing configured to contain the processor, the comparator, and the indicator.

14. The apparatus of claim 1, wherein the processor executes memory-based instructions including:

instructions for DC level component removal from the signal;

instructions for auto-correlating the signal;

instructions for windowing the signal;

instructions for producing a discrete Fourier transform (DFT) of the signal; and

instructions for calculating the flatness of the signal.

15. The apparatus of claim 14, wherein the windowing instructions perform Blackman windowing.

16. The apparatus of claim 1, wherein the transducer is disposable.

17. The apparatus of claim 1 further comprising:

a communications port for conveying signal information to an attached auxiliary device to which the apparatus is connectable.

18. The apparatus of claim 1, wherein the photo emitter operation is characterized by a single wavelength of light.

9. (canceled)

19. A non-invasive circulation monitoring method comprising:

providing an electro-optical probe having a photo emitter and a photo detector externally adjacent a subject'"'"'s extremity;

energizing the photo emitter and monitoring the photo detector over a defined window of time to obtain quasi-periodic fluctuations from the photo detector indicative of the level of circulation in the extremity; and

visually or aurally indicating to the subject a measure of circulation in the extremity.

20. The method of claim 19 further comprising on or more steps selected from the group consisting of:

converting an analog signal from the photo detector to digital waveform data;

removing a DC level component from the data to produce fluctuation data;

auto-correlating the fluctuation data to produce correlated data;

windowing the correlated data;

shifting the windowed data through a discrete Fourier transform (DFT);

calculating the flatness of the DFT data; and

deriving a circulation index from the flatness calculation data; and

comparing the derived circulation index to one or more defined threshold levels for use in the indicating.

21. The method of claim 19, wherein the indicating is performed by a visual color-differentiated LED array.

22. The method of claim 19, wherein the energizing of the photo emitter and the monitoring of the photo detector is at a single wavelength in the infrared light spectrum.

23. A method of detecting peripheral artery disease (PAD) or coronary heart disease (CHD) in a subject, the method comprising:

fitting a subject'"'"'s finger or toe with an electro-optic probe;

energizing the probe to illuminate tissue within the subject'"'"'s finger or toe;

monitoring the probe to detect cardio-rhythmic fluctuations in response to the energizing;

comparing the level of cardio-rhythmic fluctuations to a defined PAD-indicative or CHD-indicative threshold; and

determining when the cardio-rhythmic fluctuations are below the defined PAD-indicative or CHD-indicative threshold.

24. The method of claim 23 further comprising:

visually or aurally indicating to the subject the result of the determining.

25. The method of claim 24 further comprising:

recording the cardio-rhythmic fluctuations for a defined period of time.