Monitoring device and method for compensating non-linearity effects in vital signs monitoring

• US 9,668,698 B2
• Filed: 03/26/2015
• Issued: 06/06/2017
• Est. Priority Date: 04/03/2014
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Schipper, Alphonsus Tarcisius Jozef Maria
• Primary Examiner(s): Smith, Ruth S
• Application Number:
  US15/036,290
• Publication Number:
  US 20170014081A1
• Time in Patent Office: 803 Days
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• 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 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

The present invention relates to a monitoring device (10) comprising a light source (14) for emitting light into a body part (12) of a living being; a light sensor (18) for receiving light (16) including an ambient light component (30) and a measurement light component (32) resulting from interactions of said emitted light with said body part (12) and for generating an output signal (34), wherein a transfer function describes the relation between the output signal (34) and the received light; an ambient light cancellation unit (20) for separating the output signal (34) into a first signal portion (36) corresponding to the ambient light component (30) and a second signal portion (38) corresponding to the measurement light component (32); and an ambient light modulation removal unit (22) for compensating a variation of the ambient light component (30) by demodulating the second signal portion (38) based on the transfer function (f) and the first signal portion (36) to generate a measurement signal (40).

Claims

1. A monitoring device comprising:

a light source configured to emit light into a body part of a living being;

a light sensor configured to receive light including an ambient light component and a measurement light component resulting from interactions of said emitted light with said body part and configured to generate an output signal, wherein a transfer function describes the relation between the output signal and the received light; and

a microprocessor device comprising;

an ambient light cancellation unit configured to separate the output signal into a first signal portion corresponding to the ambient light component and a second signal portion corresponding to the measurement light component;

an ambient light modulation removal unit configured to compensate a variation of the ambient light component by demodulating the second signal portion based on the transfer function and the first signal portion to generate a measurement signal; and

a processing unit configured to derive and monitor information on a vital sign of the living being from the measurement signal.

2. The monitoring device of claim 1, wherein the ambient light modulation removal unit is configured to determine a derivative of the transfer function.

3. The monitoring device of claim 2, wherein the ambient light modulation removal unit is configured to demodulate the second signal portion by multiplying it with an inverse of the derivative of the transfer function.

4. The monitoring device of claim 1, wherein the ambient light cancellation unit is configured to determine an estimate for the first signal portion component and subtract said estimate from the output signal to determine the second signal portion.

5. The monitoring device of claim 1, further comprising a calibration unit configured to determine the transfer function, wherein the calibration unit is configured to determine a calibration value from the output signal of the light sensor when being exposed to calibration light of predefined intensity.

6. The monitoring device of claim 5, wherein the calibration unit is configured to apply a curve fitting algorithm to a plurality of calibration values.

7. The monitoring device of claim 1,

wherein the light source is configured to emit light pulses;

and

wherein the ambient light cancellation unit is configured to separate the output signal based on the output signal at a point in time when the light source is powered off and based on the output signal at a point in time when the light source emits light.

8. The monitoring device of claim 7,

further including a filtering unit configured to filter the output signal with a first low-pass filter when the light source emits light to generate a first filtered signal and with a second low-pass filter when the light source is powered off to generate a second filtered signal;

wherein the ambient light cancellation unit is configured to subtract the second filtered signal from the first filtered signal.

9. The monitoring device of claim 1,

further comprising an additional ambient light sensor configured to receive ambient light and for generating an ambient light signal;

wherein the ambient light cancellation unit is configured to separate the output signal based on an estimate for the ambient light component derived from the generated ambient light signal.

10. The monitoring device of claim 1, wherein the light source is configured to emit light of a first wavelength, further comprising an additional light source configured to emit light of a second wavelength different from the first wavelength.

11. The monitoring device of claim 1,

wherein the light source and the light sensor are configured to be arranged on opposite sides of the body part of the living being;

and

wherein the measurement light component of the light results from a transmission of the emitted light through said body part.

12. The monitoring device of claim 1,

wherein the light source and the light sensor are configured to be arranged to face a body part of the living being;

and

wherein the measurement light component of the light results from a reflection of the emitted light at said body part.

13. A monitoring method comprising the steps of:

emitting light into a body part of a living being;

receiving light including an ambient light component and a measurement light component resulting from interactions of said emitted light with said body part and for generating an output signal, wherein a transfer function describes the relation between the output signal and the received light;

separating the output signal into a first signal portion corresponding to the ambient light component and a second signal portion corresponding to the measurement light component;

compensating a variation of the ambient light component by demodulating the second signal portion based on the transfer function and the first signal portion to generate a measurement signal; and

deriving and monitoring information on a vital sign of the living being from the measurement signal.

14. The monitoring method of claim 13, wherein the transfer function is a non-linear function.

15. The monitoring method of claim 13, further comprising the step of determining a calibration value from the output signal of the light sensor when being exposed to calibration light of predefined intensity.