Device, system and method for determining the concentration of a substance in the blood of a subject

Patent metadata

Field	Value
Publication number	US-10531820-B2
Application number	US-201514941934-A
Country	US
Kind code	B2
Filing date	Nov 16, 2015
Priority date	Nov 24, 2014
Publication date	Jan 14, 2020
Grant date	Jan 14, 2020

Abstract

In a device, system and method for determining the concentration of a substance, such as the oxygen saturation in the blood of a subject, the influence of specular reflection is reduced or removed. An input unit is configured to receive detection signals reflected back from a skin area of the subject in response to irradiation of the skin area by a radiation signal. A signal extraction unit is configured to extract at least two photo-plethysmography, PPG, signals at two different wavelengths from the detection signals. A processing unit is configured to compute the concentration of a selected substance in the blood of the subject based on the PPG signals taking into account a skin tone of the subject.

First claim

The invention claimed is:

1. A device for determining a concentration of a substance in blood of a subject, comprising:
an input unit configured to receive detection signals indicative of radiation reflected back from a skin area of the subject in response to irradiation of the skin area,
a signal extraction unit configured to extract at least two photo-plethysmography, PPG, signals at two different wavelengths from the detection signals, and
a processing unit configured to obtain skin tone information indicative of a skin tone of the subject and compute the concentration of a desired substance in the blood of the subject based on the PPG signals, wherein the processing unit is further configured to compensate the computation for the skin tone of the subject based on the skin tone information, wherein the processing unit is further configured to at least one of:
use as a correction factor for correcting the denominator of the first normalized pulsatility at a wavelength in the red spectrum a fraction of the DC level of the PPG signal at a wavelength in the infrared spectrum,
use as a correction factor a fraction in the range of 5% to 15% of the DC level of the PPG signal at a wavelength in the infrared spectrum; and
compute arterial blood oxygen concentration from the PPG signals by

C
1

-

C
2

·

AC
R

/

DC
R

AC

I
⁢

⁢
R

/

DC

I
⁢

⁢
R

·

(

1
-
S

)

1
-

S
·

DC

I
⁢

⁢
R

/

DC
R

where
AC R /DC R is the normalized pulsatility at a wavelength in the red spectrum,
AC IR /DC IR is the normalized pulsatility at a wavelength in the infrared spectrum,
DC R is the DC level of the PPG signals at a wavelength in the red spectrum,
DC IR is the DC level of the PPG signals at a wavelength in the infrared spectrum,
C 1 and C 2 are predetermined calibration constants, and
S is an estimate of the relative specular reflection contained in the DC level of the PPG signals.

2. The device as claimed in claim 1 ,
wherein the processing unit is further configured to form a ratio of a first normalized pulsatility at a first wavelength and a second normalized pulsatility at a second wavelength for the computation of the concentration, wherein the denominator of the first and/or the second normalized pulsatility is corrected by a correction factor.

3. The device as claimed in claim 1 ,
wherein the processing unit is configured to use a value in the range of 5% to 15% for S.

4. The device as claimed in claim 1 , further including: a non-contact remote photoplethysmography (rPPG) camera configured to generate images of the skin area of the subject.

5. The device as claimed in claim 4 ,
wherein the processing unit is further configured to adapt the computation to an average intensity of the radiation reflected back from the skin area at the two different wavelengths.

6. A device for determining a concentration of a substance in blood of a subject, comprising:
an input unit configured to receive detection signals reflected back from a skin area of the subject in response to irradiation of the skin area by a radiation signal,
a signal extraction unit configured to extract at least two photo-plethysmography, PPG, signals at two different wavelengths from the detection signals, and
a processing unit configured to compute the concentration of a desired substance in the blood of the subject based on said PPG signals, wherein the computation is adapted to the skin tone of the subject,
wherein the processing unit is configured to form a ratio of a first normalized pulsatility at a first wavelength and a second normalized pulsatility at a second wavelength for the computation of the concentration, wherein the denominator of the first and/or the second normalized pulsatility is corrected by a correction factor,
wherein the correction factor is used for correcting the denominator of the first normalized pulsatility a fraction of a first DC level of the PPG signal at the second wavelength and/or is used for correcting the denominator of the second normalized pulsatility a fraction of a second DC level of the PPG signal at the first wavelength.

7. A system for determining a concentration of a target substance in the blood of a subject, comprising:
a photoplethysmography (PPG) detector configured to detect radiation in a red spectrum and an infrared spectrum reflected back from a skin area of the subject in response to irradiation of the skin area and generate detection signals indicative thereof, and
a computer processor configured to determine the concentration of the target substance in the blood corrected for a skin tone of the subject from the detection signals including:
receiving the detection signals from the PPG detector,
extracting PPG signals in the red spectrum and in the infrared spectrum from the detection signals, and
computing the concentration of the target substance based on the PPG signals, including:
computing a ratio of a normalized pulsatility in the red spectrum and the infrared spectrum, and
using a correction factor for correcting a denominator of the ratio of the normalized pulsatility in the red spectrum with a fraction of a DC level of the PPG signal in the infrared spectrum.

8. The system as claimed in claim 7 ,
wherein the PPG detector includes a remote PPG (rPPG) camera configured to obtain images of the skin area of the subject; and
a display configured to display the determined concentration.

9. A method for determining a concentration of a selected substance in the blood of a subject, comprising:
r

Assignees

• Koninklijke Philips Nv

Inventors

• De Haan Gerard
• Rocque Mukul

Classifications

• A61B5/7271

  Specific aspects of physiological measurement analysis (specific diagnostics methods using bioelectric or biomagnetic signals A61B5/316) · CPC title

• A61B2576/00

  Medical imaging apparatus involving image processing or analysis (A61B1/00009, A61B6/52 and A61B8/52 take precedence) · CPC title

• A61B5/14551

  for measuring blood gases · CPC title

• A61B5/0077 Primary

  Devices for viewing the surface of the body, e.g. camera, magnifying lens · CPC title

• A61B5/1495 Primary

  Calibrating or testing of in-vivo probes · CPC title