US-20260123862-A1 - Oxygen Saturation Measuring Device, Oxygen Saturation Measuring Method, and Oxygen Saturation Measuring Program

US20260123862A1US 20260123862 A1US20260123862 A1US 20260123862A1US-20260123862-A1

Abstract

An oxygen saturation measuring device determines a first light projection timing and a second light projection timing based on a peak timing and a bottom timing of a third pulse wave signal corresponding to a light intensity of received light of reference light in one pulsation, causes the first light emitting element to project the red light at the first light projection timing, causes the second light emitting element to project the infrared light at the second light projection timing, and measures oxygen saturation of an artery based on a first pulse wave signal output from a light receiving element according to the red light projected at the first light projection timing and a second pulse wave signal output from the light receiving element according to the infrared light projected at the second light projection timing.

Inventors

Mitsuaki KUBO
Masayuki Koizumi
Masahiro Kawachi
Yuki Matsui
Kazuo Yamamoto
Tetsuya Kiguchi
Masayuki Arakawa
Suguru OHASHI

Assignees

OMRON CORPORATION

Dates

Publication Date: 20260507
Application Date: 20231011
Priority Date: 20221019

Claims (10)

1 . An oxygen saturation measuring device, comprising: a sensor unit including a first light emitting element that projects red light to an artery, a second light emitting element that projects infrared light to the artery, a third light emitting element that projects reference light, which has a wavelength at which an absorption coefficient of oxidized hemoglobin and an absorption coefficient of reduced hemoglobin are higher than those of red light and infrared light, to the artery, and a light receiving element that receives, as received light, transmitted light or reflected light corresponding to each of the projected red light, the projected infrared light, and the projected reference light, and outputs a first pulse wave signal corresponding to a light intensity of the received light of the red light, a second pulse wave signal corresponding to a light intensity of the received light of the infrared light, and a third pulse wave signal corresponding to a light intensity of the received light of the reference light; and a processor electrically connected to the first light emitting element, the second light emitting element, and the light receiving element, and configured to determine, based on a peak timing and a bottom timing of the third pulse wave signal in one pulsation, a first light projection timing at which the first light emitting element projects the red light and a second light projection timing at which the second light emitting element projects the infrared light, cause the first light emitting element to project the red light at the determined first light projection timing, cause the second light emitting element to project the infrared light at the determined second light projection timing, and calculate oxygen saturation based on the first pulse wave signal acquired according to the light intensity of the received light of the red light projected at the first light projection timing and the second pulse wave signal acquired according to the light intensity of the received light of the infrared light projected at the second light projection timing to measure an oxygen saturation of the artery.
2 . The oxygen saturation measuring device according to claim 1 , wherein the processor is configured to: based on the peak timing and the bottom timing of the acquired third pulse wave signal, calculate a heartbeat interval of a predicted pulsation of the third pulse wave signal expected to arrive and a predicted peak timing and a predicted bottom timing in the predicted pulsation, and determine the first light projection timing and the second light projection timing in the predicted pulsation, based on the predicted peak timing and the predicted bottom timing that are calculated.
3 . The oxygen saturation measuring device according to claim 2 , wherein the processor is configured to: determine the first light projection timing and the second light projection timing in each of a first maximum side light projection period from a timing at which ⅔ of the heartbeat interval of the predicted pulsation elapses from the peak timing in a pulsation immediately before the predicted pulsation, to the predicted peak timing, and a first minimum side light projection period from the predicted bottom timing of the predicted pulsation to a timing at which ⅓ of the heartbeat interval of the predicted pulsation elapses from the predicted bottom timing.
4 . The oxygen saturation measuring device according to claim 1 , wherein the processor is configured to: set a maximum side threshold value of an amplitude, based on a maximum amplitude of the third pulse wave signal acquired at the peak timing, set a minimum side threshold value of the amplitude, based on a minimum amplitude of the third pulse wave signal acquired at the bottom timing, and determine the first light projection timing and the second light projection timing in each of a second maximum side light projection period in which the amplitude is equal to or higher than the maximum side threshold value and a second minimum side light projection period in which the amplitude is equal to or lower than the minimum side threshold value, in the pulsation of the third pulse wave signal.
5 . The oxygen saturation measuring device according to claim 4 , wherein: the maximum side threshold value is ⅔ or more of a difference between the maximum amplitude, and the minimum amplitude, and the minimum side threshold value is ⅓ or less of the difference between the maximum amplitude and the minimum amplitude.
6 . The oxygen saturation measuring device according to claim 1 , wherein the processor is configured to: calculate a coefficient of variation representing a state of pulsation based on a heartbeat interval of the acquired third pulse wave signal, execute processing 1 in a case in which the calculated coefficient of variation is equal to or less than a preset threshold value, and execute processing 2 in a case in which the coefficient of variation exceeds the threshold value, processing 1 being processing of: based on the peak timing and the bottom timing of the acquired third pulse wave signal, calculating a heartbeat interval of a predicted pulsation of the third pulse wave signal expected to arrive and a predicted peak timing and a predicted bottom timing in the predicted pulsation, and determining the first light projection timing and the second light projection timing in the predicted pulsation, based on the predicted peak timing and the predicted bottom timing that are calculated, and processing 2 being processing of: setting a maximum side threshold value of an amplitude, based on a maximum amplitude of the third pulse wave signal acquired at the peak timing, setting a minimum side threshold value of the amplitude, based on a minimum amplitude of the third pulse wave signal acquired at the bottom timing, and determining the first light projection timing and the second light projection timing in each of a second maximum side light projection period in which the amplitude is equal to or higher than the maximum side threshold value and a second minimum side light projection period in which the amplitude is equal to or lower than the minimum side threshold value, in the pulsation of the third pulse wave signal.
7 . The oxygen saturation measuring device according to claim 6 , wherein a threshold value of the coefficient of variation is 0.1 or less.
8 . The oxygen saturation measuring device according to claim 1 , which is a wearable device that is wearable by a subject.
9 . An oxygen saturation measuring method comprising: projecting, to an artery, reference light having a wavelength at which an absorption coefficient of oxidized hemoglobin and an absorption coefficient of reduced hemoglobin are higher than those of red light and infrared light; receiving, as received light, transmitted light or reflected light corresponding to the projected reference light; acquiring a third pulse wave signal corresponding to a light intensity of the received light of the reference light; based on a peak timing and a bottom timing of the acquired third pulse wave signal in one pulsation, determining a first light projection timing at which the red light is projected and a second light projection timing at which the infrared light is projected; projecting the red light at the determined first light projection timing; projecting the infrared light at the determined second light projection timing; and calculating oxygen saturation based on a first pulse wave signal acquired according to a light intensity of the received light of the transmitted light or the reflected light corresponding to the red light projected at the first light projection timing and a second pulse wave signal acquired according to a light intensity of the received light of the transmitted light or the reflected light corresponding to the infrared light projected at the second light projection timing to measure an oxygen saturation of the artery.
10 . A non-transitory storage medium storing a program executable by a computer to perform oxygen saturation measurement processing, the processing comprising: projecting, to an artery, reference light having a wavelength at which an absorption coefficient of oxidized hemoglobin and an absorption coefficient of reduced hemoglobin are higher than those of red light and infrared light; receiving, as received light, transmitted light or reflected light corresponding to the projected reference light; acquiring a third pulse wave signal corresponding to a light intensity of the received light of the reference light; based on a peak timing and a bottom timing of the acquired third pulse wave signal in one pulsation, determining a first light projection timing at which the red light is projected and a second light projection timing at which the infrared light is projected; projecting the red light at the determined first light projection timing; projecting the infrared light at the determined second light projection timing; and calculating oxygen saturation based on a first pulse wave signal acquired according to a light intensity of the received light of the transmitted light or the reflected light corresponding to the red light projected at the first light projection timing and a second pulse wave signal acquired according to a light intensity of the received light of the transmitted light or the reflected light corresponding to the infrared light projected at the second light projection timing to measure an oxygen saturation of the artery.

Description

TECHNICAL FIELD The present disclosure relates to an oxygen saturation measuring device, an oxygen saturation measuring method, and an oxygen saturation measuring program. BACKGROUND ART Hitherto, as an example of a method of measuring oxygen saturation (SPO2) in arterial blood, a measuring method using an absorption spectroscopy as in Japanese Patent Application Laid-Open (JP-A) No. 2008-167868 is known. In JP-A No. 2008-167868, red light and infrared light having wavelengths different from each other are projected to arterial blood, and transmitted light or reflected light corresponding to each light is received by a light receiving element. Hereinafter, for convenience of description, light received by the light receiving element, such as the transmitted light and the reflected light, is collectively referred to as “received light”. Specifically, amplitudes of a plurality of pulse wave signals are calculated for each of the red light and the infrared light from a maximum value and a minimum value acquired from the pulse wave signals of the received light. In order to increase the number of acquired pieces of data for amplitude calculation, usually, a light projection interval and a light reception interval of the red light and the infrared light for measurement are repeated a plurality of times at an interval shorter than one heartbeat interval of an artery to be measured. A fluctuation component (AC) and a fixed component (DC) of the pulse wave signal are calculated from the plurality of calculated amplitudes, and a perfusion index (PI value) of each of the red light and the infrared light is calculated from the calculated fluctuation component and fixed component. Then, the oxygen saturation as a measured value can be calculated by introducing a ratio of the PI value of the red light to the PI value of the infrared light (that is, an absorbance ratio) into a preset calculation formula for oxygen saturation calculation. Further, in JP-A No. 2008-167868, predetermined pulse wave information such as a sampling number and a pulse rate of the pulse wave signal obtained by one pulsation is obtained from a pulse wave signal output corresponding to a light intensity of the received light. In JP-A No. 2008-167868, as an interval of a light emission time of a light emitting element is set based on the obtained pulse wave information, the oxygen saturation can be measured with high accuracy and power consumption of an oxygen saturation measuring device can be reduced. CITATION LITERATURE Patent Literature Patent Literature 1: JP-ANo. 2008-167868 SUMMARY OF INVENTION Technical Problem Here, since a signal-to-noise (SN) ratio decreases as a blood flow is relatively low perfusion, that is, the light intensity of the pulse wave signal of the received light is low, accuracy in calculation of the amplitude of the pulse wave signal decreases. In this regard, in JP-A No. 2008-167868, only the pulse wave signals of the received light of the red light and the infrared light are used for measurement. Therefore, in a case in which the SN ratio of the pulse wave signal of the received light is low, accuracy of the pulse wave information obtained from the pulse wave signal also decreases, or necessary pulse wave information cannot be obtained. As a result, it is difficult to set the interval of the light emission time based on the pulse wave information. The present disclosure has been made focusing on the above, and provides an oxygen saturation measuring device, an oxygen saturation measuring method, and an oxygen saturation measuring program capable of improving measurement accuracy. Solution to Problem An oxygen saturation measuring device according to a first aspect of the present disclosure includes: a sensor unit including a first light emitting element that projects red light to an artery, a second light emitting element that projects infrared light to the artery, a third light emitting element that projects reference light, which has a wavelength at which an absorption coefficient of oxidized hemoglobin and an absorption coefficient of reduced hemoglobin are higher than those of red light and infrared light to the artery, and a light receiving element that receives, as received light, transmitted light or reflected light corresponding to each of the projected red light, the projected infrared light, and the projected reference light, and outputs a first pulse wave signal corresponding to a light intensity of the received light of the red light, a second pulse wave signal corresponding to a light intensity of the received light of the infrared light, and a third pulse wave signal corresponding to a light intensity of the received light of the reference light; and a processor electrically connected to the first light emitting element, the second light emitting element, and the light receiving element and configured to determine, based on a peak timing and a bottom timing of the third pulse wave signal in one pulsation,