PHOTOPLETHYSMOGRAPHY

• US 20140243622A1
• Filed: 05/14/2014
• Published: 08/28/2014
• Est. Priority Date: 04/11/2006
• Status: Active Grant

• Current Assignee: University of Nottingham
• Original Assignee: University of Nottingham
• Inventors: CROWE, John, HAYES-GILL, Barrie, GRUBB, Mark, MILES, Nicolas
• Granted Patent: US 11,103,150 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• 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 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• CPC Class Codes: A61B 5/7235 Details of waveform analysis A61B5/349 takes precedence

Abstract

A photoplethysmograph device includes a light source for illuminating a target object. A modulator drives the light source such that the output intensity varies as a function of a modulation signal at a modulation frequency. A detector receives light from the target object and generates an electrical output as a function of the intensity of received light. A demodulator with a local oscillator receives the detector output and produces a demodulated output, insensitive to any phase difference between the modulation signal and the oscillator, indicative of blood volume as a function of time and/or blood composition. A number of demodulators may be provided to derive signals from multiple light sources of different wavelengths, or from an array of detectors. The plethysmograph may operate in a transmission mode or a reflectance mode. When in a reflectance mode, the device may use the green part of the optical spectrum and may use polarising filters.

Claims

1. A photoplethysmograph device comprising:

a plurality of light sources each for illuminating a portion of a target object, each of the plurality of light sources having an optical output at a different wavelength;

one or more modulators for driving the light sources such that the output intensity of each light source varies as a function of a modulation signal at a modulation frequency;

one or more detectors for receiving light from the target object and generating one or more electrical outputs as a function of the intensity of received light;

a plurality of demodulators each for receiving one or more of the electrical outputs, each one of the plurality of demodulators producing a demodulated output representative of the modulation signal and any sidebands thereof of a respective different one of the optical wavelengths, to thereby produce a plurality of demodulated outputs corresponding to the plurality of light sources and/or plurality of detectors;

means for generating, from the demodulated outputs, photoplethysmogram signals indicative of blood volume as a function of time and/or blood composition for each of the demodulator outputs; and

means for selecting one of the demodulated outputs that provides the best signal-to-noise ratio.

4. The photoplethysmograph device of claim 1 further including means for performing one or more of independent component analysis, principal component analysis and blind source separation from the multiple demodulator outputs to improve the signal to noise ratio.

5. The photoplethysmograph device of claim 1 wherein the plurality of light sources are disposed in a pixel array on a substrate.

6. The photoplethysmograph device of claim 5 further including means for mapping the spatial distribution of the blood volume and/or blood composition correlated with the relative spatial locations of the light sources in the pixel array.

7. The photoplethysmograph device of claim 1 wherein the light sources are driven at different modulation frequencies.

8. The photoplethysmograph device of claim 7 in which the demodulators each produce a demodulated output corresponding to a respective one of the light sources.

9. The photoplethysmograph device of claim 1 including a plurality of detectors each operative to receive light at a respective one of the light source wavelengths and in which the demodulators each produce a demodulated output corresponding to a respective one of the light sources.

10. The photoplethysmograph device of claim 1 in which the demodulators each have a local oscillator and produce a demodulated output representative of the respective modulation signal, in which the demodulator is insensitive to any phase difference between the respective modulation signal and the oscillator of the demodulator.

11. The photoplethysmograph device of claim 1 in which the light sources and one or more detectors are disposed laterally adjacent to one another on a substrate such that the active surfaces thereof can be directed towards substantially the same point on a surface of the target body.

12. The photoplethysmograph device of claim 1 including plural detectors and corresponding plural demodulators each disposed in a pixel array on a substrate.

13. The photoplethysmograph device of claim 12 further including means for mapping the spatial distribution of the blood volume and/or blood composition correlated with the relative spatial locations of the detectors in the pixel array

27. The photoplethysmograph device of claim 10, wherein the demodulator is a digital signal processing demodulator and:

the local oscillator is configured to produce a first square wave output at an oscillator frequency and at a first phase angle, and a second square wave output at the oscillator frequency and at a second phase angle, the second phase angle being at 90 degrees to the first phase angle; and

the demodulator is configured to multiply the detector output with the first square wave output and the second square wave output to produce an I signal and a Q signal respectively.

28. The photoplethysmograph device of claim 27, wherein the demodulator is configured to low-pass filter and decimate the I signal and Q signal to produce a low-pass filtered and decimated I′

signal and Q′

signal, the I′

signal and Q′

signal being de-multiplexed together to form the demodulated output.

29. The photoplethysmograph device of claim 28, wherein the demodulator is configured to filter and decimate the I signal and Q signal by summing samples in blocks, wherein the number of samples in a block equals the sample frequency divided by the oscillator frequency.

2. (canceled)

3. (canceled)

14. A method of generating a photoplethysmogram, comprising the steps of:

illuminating a portion of a target object with a plurality of light sources;

driving the plurality of light sources with one or more modulators such that the output intensity of each light source varies as a function of a modulation signal at a modulation frequency;

receiving light from the target object with one or more detectors and generating one or more electrical outputs as a function of the intensity of received light;

receiving one or more of the electrical outputs with a plurality of demodulators, each producing a demodulated output representative of the modulation signal of one of the modulated light sources and any sidebands thereof, to thereby produce a plurality of demodulated outputs corresponding to the plurality of light sources;

generating, from the demodulated outputs, plethysmogram signals indicative of blood volume as a function of time and/or blood composition for each of the demodulator outputs; and

selecting one of the demodulated outputs that provides the best signal-to-noise ratio.

15. A photoplethysmograph device for non-contact use, comprising:

a first and second polarising filter;

a light source arranged to illuminate a target object via the first polarising filter;

a modulator for driving the light source such that the output intensity varies as a function of a modulation signal at a modulation frequency;

a detector arranged to receive light from the target object via the second polarising filter having a different polarisation state than the first polarising filter, the detector adapted to generate an electrical output as a function of the intensity of received light;

a demodulator for receiving the detector output and producing a demodulated output representative of the modulation signal and any sidebands thereof; and

means for generating, from the demodulated output, a signal indicative of blood volume as a function of time and/or blood composition.

16. The photoplethysmograph device of claim 15 in which the first and second polarising filters are disposed with their relative polarisation states at 90 degrees to one another.

17. The photoplethysmograph device of claim 15 in which the detector has a local oscillator and produces a demodulated output representative of the modulation signal, in which the demodulator is insensitive to any phase difference between the modulation signal and the oscillator of the demodulator.

18. The photoplethysmograph device of claim 15 in which the light source and detector are disposed laterally adjacent to one another on a substrate such that the active surfaces thereof can be directed towards substantially the same point on a surface of the target body.

19. The photoplethysmograph device of claim 15 in which the light source has an optical output of wavelength less than 600 nm.

20. The photoplethysmograph device of claim 19 in which the light source has an optical output of wavelength between 440 nm and 574 nm or between 500 nm and 600 nm.

30. The photoplethysmograph device of claim 17, wherein the demodulator is a digital signal processing demodulator and:

the local oscillator is configured to produce a first square wave output at an oscillator frequency and at a first phase angle, and a second square wave output at the oscillator frequency and at a second phase angle, the second phase angle being at 90 degrees to the first phase angle; and

the demodulator is configured to multiply the detector output with the first square wave output and the second square wave output to produce an I signal and a Q signal respectively.

31. The photoplethysmograph device of claim 30, wherein the demodulator is configured to low-pass filter and decimate the I signal and Q signal to produce a low-pass filtered and decimated I′

signal and Q′

signal, the I′

signal and Q′

signal being de-multiplexed together to form the demodulated output.

32. The photoplethysmograph device of claim 31, wherein the demodulator is configured to filter and decimate the I signal and Q signal by summing samples in blocks, wherein the number of samples in a block equals the sample frequency divided by the oscillator frequency.

21. A method of generating a photoplethysmogram, comprising the steps of:

illuminating a target object with a light source via a first polarising filter;

driving the light source with a modulator such that the output intensity varies as a function of a modulation signal at a modulation frequency;

receiving light from the target object with a detector via a second polarising filter having a different polarisation state than the first polarising filter, the detector generating an electrical output as a function of the intensity of received light;

receiving the detector output with a demodulator and producing a demodulated output representative of the modulation signal and any sidebands thereof; and

generating, from the demodulated output, a signal indicative of blood volume as a function of time and/or blood composition.

22-26. -26. (canceled)

33. A photoplethysmograph device comprising:

one or more light sources each for illuminating a portion of a target object;

one or more modulators for driving the light sources such that the output intensity of each light source varies as a function of a modulation signal at a modulation frequency;

a pixel array, each pixel comprising;

a detector for receiving light from the target object and generating an electrical output as a function of the intensity of received light; and

a demodulator for receiving the electrical output and producing a demodulated output representative of the modulation signal and any sidebands thereof;

and

further comprising means for generating, from the demodulated outputs of each pixel, photoplethysmogram signals indicative of blood volume as a function of time and/or blood composition for each of the demodulator outputs.

34. The photoplethysmograph device of claim 33, wherein each pixel responds to light from a common light source.

35. The photoplethysmograph device of claim 33, wherein the common light source is modulated with a common modulation frequency.

36. The photoplethysmograph device of claim 33, wherein an independently driven light source is provided corresponding with each pixel, and each pixel is responsive to a corresponding light source.

37. The photoplethysmograph device of claim 36, wherein each light source is modulated with a common modulation frequency.

38. The photoplethysmograph device of claim 36, wherein each light source is driven with a different modulation frequency.

39. The photoplethysmograph device of claim 33, further comprising a signal processor operable to perform at least one of:

blind source separation, independent component analysis and principle component analysis on the demodulated output from the pixels.

40. The photoplethysmograph device of claim 33 in which the demodulator of each pixel has a local oscillator and is configured to produce a demodulated output representative of the respective modulation signal, in which the demodulator is insensitive to any phase difference between the respective modulation signal and the oscillator of the demodulator.

41. The photoplethysmograph device of claim 40, wherein each demodulator is a digital signal processing demodulator and:

the local oscillator is configured to produce a first square wave output at an oscillator frequency and at a first phase angle, and a second square wave output at the oscillator frequency and at a second phase angle, the second phase angle being at 90 degrees to the first phase angle; and

the demodulator is configured to multiply the detector output with the first square wave output and the second square wave output to produce an I signal and a Q signal respectively.

42. The photoplethysmograph device of claim 41, wherein each demodulator is configured to low-pass filter and decimate the I signal and Q signal to produce a low-pass filtered and decimated I′

signal and Q′

signal, the I′

signal and Q′

signal being de-multiplexed together to form the demodulated output.

43. The photoplethysmograph device of claim 42, wherein each demodulator is configured to filter and decimate the I signal and Q signal by summing samples in blocks, wherein the number of samples in a block equals the sample frequency divided by the oscillator frequency.

44. A method of generating a photoplethysmogram, comprising the steps of:

illuminating a portion of a target object with at least one or more light source;

driving the plurality of light sources with one or more modulators such that the output intensity of each light source varies as a function of a modulation signal at a modulation frequency;

at each pixel of a pixel array;

receiving light from the target object with a detector and generating an electrical outputs as a function of the intensity of received light; and

receiving one or more of the electrical outputs with a demodulator, to produce a demodulated output representative of the modulation signal of the at least one modulated light source and any sidebands thereof,

so as to produce a plurality of demodulated outputs corresponding to each pixel; and

generating, from the demodulated outputs, photoplethysmogram signals indicative of blood volume as a function of time and/or blood composition for each of the demodulator outputs of the pixel array.