WO2026014387A1 - Physiological information processing system, processing device, and non-transitory computer-readable medium - Google Patents

Physiological information processing system, processing device, and non-transitory computer-readable medium

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Publication number
WO2026014387A1
WO2026014387A1 PCT/JP2025/024227 JP2025024227W WO2026014387A1 WO 2026014387 A1 WO2026014387 A1 WO 2026014387A1 JP 2025024227 W JP2025024227 W JP 2025024227W WO 2026014387 A1 WO2026014387 A1 WO 2026014387A1
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WIPO (PCT)
Prior art keywords
light
signal
living tissue
difference value
acquire
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PCT/JP2025/024227
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French (fr)
Inventor
Hideaki Hirabara
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Nihon Kohden Corp
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Nihon Kohden Corp
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Publication of WO2026014387A1 publication Critical patent/WO2026014387A1/en
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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue
    • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • A61B5/14552—Details of sensors specially adapted therefor
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0048—Detecting, measuring or recording by applying mechanical forces or stimuli
    • A61B5/0053—Detecting, measuring or recording by applying mechanical forces or stimuli by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/026—Measuring blood flow
    • A61B5/0261—Measuring blood flow using optical means, e.g. infrared light

Definitions

  • the presently disclosed subject matter relates to a system for processing physiological information of a subject.
  • the presently disclosed subject matter also relates to a processing device included in the system, as well as a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in the processing device.
  • Japanese Patent Publication No. 2021-115640A discloses an apparatus for estimating a capillary refill time (CRT). Specifically, light with a wavelength that is to be absorbed by blood is incident on a living tissue such as a fingertip, and the intensity of the light that has passed through the living tissue is measured. As the living tissue is compressed, blood is eliminated from the living tissue, whereby the intensity of the transmitted light is increased. As the compression is cancelled, the living tissue is refilled with blood, whereby the intensity of the transmitted light is decreased.
  • the CRT is estimated based on a time period from a timing when the compression is cancelled, to a timing when the transmitted light intensity returns to the original level.
  • the CRT is also used as an index reflecting a blood volume in the tissue of the subject.
  • a first illustrative aspect of the presently disclosed subject matter may provide a physiological information processing system, comprising: a light emitting device configured to emit: first light including a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and second light including a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin; a light detecting device configured to output a first signal and a second signal respectively corresponding to an intensity of the first light and an intensity of the second light that have passed through a living tissue of a subject; and a processing device configured to receive the first signal and the second signal, wherein the processing device is configured to: acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed; acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light
  • a second illustrative aspect of the presently disclosed subject matter may provide a processing device, comprising: an interface configured to receive: a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin; and a processor configured to: acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed; acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and acquire an index corresponding to an oxygen saturation of blood contained in the
  • a third illustrative aspect of the presently disclosed subject matter may provide a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to: receive a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; receive a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin; acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed; acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal
  • the living tissue includes blood and tissues other than blood.
  • the first difference value reflects the light attenuation of the tissues other than the blood.
  • the second difference value reflects both the light attenuation of the blood and the light attenuation of the tissues other than the blood.
  • the difference value between the first difference value and the second difference value may be an index that more accurately reflects the change of the oxygen saturation of the blood.
  • the constant first difference value can be handled as a reference value, it is possible to keep monitoring the second difference value as the index once a single compression of the living tissue is performed and then the second difference value is acquired intermittently or continuously.
  • a fourth illustrative aspect of the presently disclosed subject matter may provide a physiological information processing system, comprising: a light emitting device configured to emit light having a wavelength included in a range from 800nm to 950nm; a light detecting device configured to output a signal corresponding to an intensity of the light that has passed through a living tissue of a subject; and a processing device configured to receive the signal, wherein the processing device is configured to: acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed; acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
  • a fifth illustrative aspect of the presently disclosed subject matter may provide a processing device, comprising: an interface configured to receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm; and a processor configured to: acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed; acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
  • a sixth illustrative aspect of the presently disclosed subject matter may provide a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to: receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm; acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed; acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
  • the living tissue includes blood and tissues other than blood.
  • the first light attenuation reflects the light attenuation of the tissues other than the blood.
  • the second light attenuation reflects both the light attenuation of the blood and the light attenuation of the tissues other than the blood.
  • the difference value between the first light attenuation and the second light attenuation may be an index that more accurately reflects the volume change of the blood.
  • the constant first light attenuation can be handled as a reference value, it is possible to keep monitoring the second light attenuation as the index once a single compression of the living tissue is performed and then the second light attenuation is acquired intermittently or continuously.
  • FIG. 1 illustrates a functional configuration of a pulse oximeter according to an exemplary embodiment.
  • FIG. 2 is a diagram for explaining processing to be performed by the processing device of FIG. 1.
  • FIG. 3 is a diagram for explaining processing to be performed by the processing device of FIG. 1.
  • FIG. 4 is a diagram for explaining processing to be performed by the processing device of FIG. 1.
  • FIG. 5 illustrates a functional configuration of a photometry system according to another exemplary embodiment.
  • FIG. 1 illustrates a functional configuration of a pulse oximeter 10 according to an exemplary embodiment.
  • the pulse oximeter 10 is a device configured to calculate a transcutaneous arterial oxygen saturation (SpO2) of a subject based on a concentration of a light absorber contained in arterial blood of the subject.
  • SpO2 transcutaneous arterial oxygen saturation
  • the pulse oximeter 10 is an example of a physiological information processing system.
  • the pulse oximeter 10 includes a light emitting device 11.
  • the light emitting device 11 includes a first light emitting element 111 and a second light emitting element 112.
  • the first light emitting element 111 is configured to emit first light including a first wavelength ⁇ 1.
  • the second light emitting element 112 is configured to emit second light including the second wavelength ⁇ 2.
  • the first wavelength ⁇ 1 is selected as a wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin.
  • Examples of the first wavelength ⁇ 1 include 940 nm.
  • the second wavelength ⁇ 2 is selected as a wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin.
  • Examples of the second wavelength ⁇ 2 include 660 nm.
  • Each of the first light emitting element 111 and the second light emitting element 112 may be a semiconductor light emitting element.
  • the semiconductor light emitting element include a light emitting diode, a laser diode, and an EL element.
  • the pulse oximeter 10 includes a light detecting device 12.
  • the light detecting device 12 includes a light detecting element.
  • the light detecting element is configured to output a first signal I1 and a second signal I2 respectively corresponding to the intensity of the first light and the intensity of the second light at a light detecting surface.
  • Each of the first signal I1 and the second signal I2 may be an analog signal or a digital signal.
  • Examples of the light detecting element include a photodiode, a phototransistor, and a photoresistor.
  • the pulse oximeter 10 includes a processing device 13.
  • the processing device 13 includes an input interface 131.
  • the input interface 131 is configured to receive the first signal I1 and the second signal I2 that are outputted from the light detecting device 12.
  • the input interface 131 is provided with an adequate conversion circuit including an A/D converter. This description is similarly applied to other signals that can be received by the input interface 131 and that will be described later.
  • the processing device 13 includes a processor 132.
  • the processor 132 is configured to execute processing for implementing various functions described later.
  • the processing device 13 includes an output interface 133.
  • the output interface 133 is configured to output an emission control signal EC for causing the light emitting device 11 to perform a prescribed light emitting operation.
  • the emission control signal EC may be an analog signal or a digital signal in accordance with the specification of the light emitting device 11.
  • the output interface 133 is provided with an adequate conversion circuit including a D/A converter. This description is similarly applied to other signals that can be outputted from the output interface 133 and that will be described later.
  • the processor 132 outputs an emission control signal EC that causes the light emitting device 11 to alternately emit the first light and the second light, from the output interface 133.
  • the first light emitting element 111 and the second light emitting element 112 alternately emit the first light and the second light at a timing specified by the emission control signal EC.
  • the first light and the second light are alternately incident on a living tissue T of the subject.
  • the first light and the second light that have passed through the living tissue T are alternately incident on the light detecting surface of the light detecting device 12.
  • the light detecting device 12 alternately outputs the first signal I1 and the second signal I2.
  • the processor 132 of the processing device 13 identifies which signal is received by the input interface 131 based on the timing at which the light emission control of the first light emitting element 111 and the second light emitting element 112 is performed.
  • the processor 132 is configured to calculate the SpO2 of the subject based on the intensities of the first and second signals I1 and I2.
  • a light attenuation A1 of the first light and a light attenuation A2 of the second light in connection with the passage through the living tissue T can be calculated from the intensities of the first light and the second light at the light detecting device 12 that correspond to the first signal I1 and the second signal I2.
  • the SpO2 has a correlation with a ratio of the light attenuation A1 of the first light and the light attenuation A2 of the second light. Accordingly, the value of SpO2 may be calculated by inputting the ratio to a function corresponding to the correlation.
  • the light attenuation A1 of the first light is expressed by the following equation.
  • Ab1 a light attenuation of the first light that can be attributed to blood
  • At1 a light attenuation of the first light that can be attributed to tissues other than the blood
  • Eb1 an absorbance (dL g -1 cm -1 ) of the blood with respect to the first light
  • Hb a hemoglobin concentration in blood (g dL -1 )
  • Db a blood thickness (cm)
  • Zt1 a light attenuation rate (cm -1 ) of the first light in the tissues other than the blood
  • Dt a thickness (cm) of the tissues other than the blood
  • the light attenuation A2 of the second light is expressed by the following equation.
  • Ab2 a light attenuation of the second light that can be attributed to the blood
  • At2 a light attenuation of the second light that can be attributed to the tissues other than the blood
  • Eb2 an absorbance (dL g -1 cm -1 ) of the blood with respect to the second light
  • Zt2 a light attenuation rate (cm -1 ) of the second light in the tissues other than the blood
  • the compression may be performed with a hand of a user, or may be performed mechanically with an actuator or the like.
  • FIG. 2 illustrates changes over time of the difference value ⁇ A that is calculated as described above.
  • the compression is initiated at a time point t1
  • blood is eliminated from the living tissue T, whereby the intensities of the first light and the second light as detected increase. Accordingly, the difference value ⁇ A is increased as well.
  • the compression is cancelled at a time point t2
  • blood returns to the living tissue T, whereby the intensities of the first light and the second light as detected decrease. Accordingly, the difference value ⁇ A is decreased as well.
  • the processor 132 is configured to acquire, based on the first signal I1 and the second signal I2 that are received by the input interface 131 during the compression of the living tissue T, a difference value between the light attenuation A1 of the first light and the light attenuation A2 of the second light during the compression, as a first difference value ⁇ Ap1.
  • the first difference value ⁇ Ap1 may be acquired as a difference value at an arbitrary time point during a time period from the time point t1 to the time point t2 in FIG. 2, or may be acquired as a statistic value of the difference value at an arbitrary time slot during the time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
  • the processor 132 is configured to acquire, based on the first signal I1 and the second signal I2 that are received by the input interface 131 after the compression of the living tissue T is cancelled, a difference value between the light attenuation A1 of the first light and the light attenuation A2 of the second light during the compression, as a second difference value ⁇ Ap2.
  • the second difference value ⁇ Ap2 may be acquired as a difference value at an arbitrary time point during a time period after the time point t3 in FIG. 2, or may be acquired as a statistic value of the difference value at an arbitrary time slot during the time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
  • the processor 132 In order to acquire the first difference value ⁇ Ap1 and the second difference value ⁇ Ap2 at an adequate timing, the processor 132 needs to recognize that the living tissue T is compressed.
  • the pulse oximeter 10 may notify the user of the timing of the initiation and cancellation of the compression through a notification mechanism (not illustrated).
  • the notification may be performed through at least one of visual notification, audible notification, and haptic notification.
  • the processor 132 may output, from the output interface 133, a control signal that controls the operation of the notification mechanism.
  • the processor 132 may recognize the output timing of the control signal in association with the time period during which the compression is performed.
  • the processor 132 may output, from the output interface 133, a control signal for controlling the operation of the actuator.
  • the processor 132 may recognize the output timing of the control signal in association with the time period during which the compression is performed.
  • the initiation and cancellation of the compression may be determined in accordance with the fact that a variation of the difference value ⁇ A as acquired exceeds a threshold.
  • the processor 132 is configured to subsequently calculate a difference value ⁇ Ab between the first difference value ⁇ Ap1 and the second difference value ⁇ Ap2.
  • ⁇ Ab ⁇ Ap2 - ⁇ Ap1 ...(4)
  • the living tissue T includes blood Tb and tissues To other than the blood. Since the blood Tb is eliminated by the compression, the first difference value ⁇ Ap1 reflects the light attenuation that can be attributed to the tissues To other than the blood. On the other hand, since the blood Tb returns by the cancellation of the compression, the second difference value ⁇ Ap2 reflects both the light attenuation that can be attributed to the blood Tb and the light attenuation that can be attributed to the tissues To other than the blood.
  • the difference value ⁇ Ab between the first difference value ⁇ Ap1 and the second difference value ⁇ Ap2 may be an index that more accurately reflects the change of the oxygen saturation of the blood Tb.
  • the constant first difference value ⁇ Ap1 can be handled as a reference value, it is possible to keep monitoring the second difference value ⁇ Ap2 as the index once a single compression of the living tissue T is performed and then the second difference value ⁇ Ap2 is acquired intermittently or continuously.
  • the pulse oximeter 10 may include an output device 14.
  • the processor 132 of the processing device 13 outputs, from the output interface 133, an output control signal OC that causes the output device 14 to output information indicating the difference value ⁇ Ab as the index as acquired.
  • the output device 14 is configured to output information indicating the difference value ⁇ Ab based on the output control signal OC.
  • the information may be visually provided using at least one of a text, a mark, and a color corresponding to the difference value ⁇ Ab.
  • the visual presentation of the information may be provided as an image that is displayed on a display or projected by a projector, or may be provided as a printed matter. Additionally or alternatively, the information may be audibly provided through a speaker.
  • the output device 14 may be a data output device that outputs the information to be subjected to processing for acquiring another index or physiological information.
  • the processing may be performed in the pulse oximeter 10, or may be performed in an external device that is independent from the pulse oximeter 10.
  • the input interface 131 of the processing device 13 may be configured to receive a measurement signal M corresponding to a measured concentration value of the hemoglobin in blood of the subject from a user interface (not illustrated).
  • the processor 132 is configured to acquire the light attenuation A1 of the first light and the light attenuation A2 of the second light based on the measurement signal M.
  • the value of Hb indicating the hemoglobin concentration in blood that is included in the above-described the equations (1) and (2) is a constant that is commonly used as a statistic value.
  • the actual hemoglobin concentration may have a value different from the constant.
  • the processor 132 according to the present example is configured to use the value of the hemoglobin concentration corresponding to the measurement signal M as the value of Hb in the equations (1) and (2) to acquire the light attenuation A1 of the first light and the light attenuation A2 of the second light.
  • the actual hemoglobin concentration in blood that would be different in accordance with the subject and/or the physical condition can be reflected in the difference value ⁇ Ab that is acquired as the index. Accordingly, the accuracy of the index can be improved.
  • the processor 132 acquires an index corresponding to the blood volume contained in the living tissue T.
  • the processor 132 acquires a light attenuation A11 of the first light during the compression of the living tissue T, based on the first signal I1 that is received by the input interface 131 during the time period.
  • the light attenuation A11 is an example of a first light attenuation. Since blood is eliminated from the living tissue T during the compression, the light attenuation A11 is substantially expressed by the following equation based on analogy to the equation (1).
  • A11 At11 ...(5)
  • At11 a light attenuation of the first light that can be attributed to the tissues other than the blood during the compression
  • the light attenuation A11 may be acquired as a value measured at an arbitrary time point during a time period from the time point t1 to the time point t2 in FIG. 2, or may be acquired as a statistic value of values measured at arbitrary time points during that time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
  • the processor 132 acquires a light attenuation A12 of the first light after the compression of the living tissue T is cancelled, based on the first signal I1 that is received by the input interface 131during that time period.
  • the light attenuation A12 is an example of a second light attenuation.
  • the light attenuation A12 is expressed by the following equation based on analogy to the equation (1).
  • A12 Ab12 + At12 ...(6)
  • Ab12 a light attenuation of the first light that can be attributed to the blood after the cancellation of the compression
  • At12 a light attenuation of the first light that can be attributed to the tissues other than the blood after the cancellation of the compression
  • the light attenuation A12 may be acquired as a value measured at an arbitrary time point that is not earlier than the time point t3 in FIG. 2, or may be acquired as a statistic value of values measured at arbitrary time points during that time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
  • the processor 132 calculates a difference value ⁇ A1 between the light attenuation A11 and the light attenuation A12.
  • the living tissue T includes blood Tb and tissues To other than blood. Since the blood Tb is eliminated by the compression, the light attenuation A11 reflects the light attenuation that can be attributed to the tissues To other than the blood. On the other hand, since the blood Tb returns by the cancellation of the compression, the light attenuation A12 reflects both the light attenuation that can be attributed to the blood Tb and the light attenuation that can be attributed to the tissues To other than the blood.
  • the difference value ⁇ A1 between the light attenuation A11 and the light attenuation A12 may be an index that more accurately reflects the volume change of the blood Tb.
  • the constant light attenuation A11 can be handled as a reference value, it is possible to keep monitoring the light attenuation A12 as the index once a single compression of the living tissue T is performed and then the light attenuation A12 is acquired intermittently or continuously.
  • the processor 132 may acquire a light attenuation A10 of the first light before the compression of the living tissue T (between the time points t0 and t1 in FIG. 2) based on the first signal I1 that is received by the input interface 131 during that period.
  • the light attenuation A10 is also an example of the second light attenuation.
  • the light attenuation A10 is expressed by the following equation.
  • A10 Ab10 + At10 ...(8)
  • At10 a light attenuation of the first light that can be attributed to the tissues other than the blood before the compression
  • the light attenuation A10 may be acquired as a measured value at an arbitrary time point during a time period from the time point t0 to the time point t1 in FIG. 2, or may be acquired as a statistic value of the measured value at an arbitrary time period during the time period.
  • the statistic value include a mean value, an intermediate value, and a mode value.
  • the processor 132 calculates a difference value ⁇ A1’ between the light attenuation A10 and the light attenuation A11.
  • the processor 132 may be configured to acquire the light attenuation A12 based on the measurement signal M illustrated in FIG. 1. Similarly to the example described with reference to the equation (1), the processor 132 is configured to use the value of the hemoglobin concentration corresponding to the measurement signal M as the value of Hb that can be included in the term of A12 in the equation (6) to acquire the light attenuation A12.
  • the actual hemoglobin concentration in blood that would be different in accordance with the subject and/or the physical condition can be reflected in the difference value ⁇ A1 that is acquired as the index. Accordingly, the accuracy of the index can be improved.
  • a capillary refill time (CRT) of the living tissue T can be specified based on the changes with time of the difference value ⁇ A as illustrated in FIG. 2. Specifically, the CRT is specified as a time period from the time point t2 when the compression is cancelled, to the time point t3 when the transmitted light intensity can be regarded as returning to the original level.
  • the difference value ⁇ A1 and the CRT that are acquired with the compression of the living tissue T are referred to as a reference difference value ⁇ A1r, and a reference CRT (rCRT).
  • eCRT ( ⁇ A1r / ⁇ A1) rCRT
  • the processor 132 may be configured to estimate a value of the CRT based on the difference value ⁇ A1 as the index that is continuously acquired after the compression of the living tissue T. Specifically, an estimated value (eCRT) of the CRT is calculated by the following equation.
  • the monitoring of the estimated value of the CRT can be continued without repeating the compression of the living tissue T.
  • the processor 132 may be configured to cause the pulse oximeter 10 to perform a notification prompting the acquisition of specific physiological information based on the difference value ⁇ A1 as the index that is acquired as described above. For example, in response to a determination that that the difference value ⁇ A1 as acquired is not within a prescribed threshold range, a notification prompting reacquisition of the CRT involving the compression of the living tissue T may be performed.
  • the fact that the difference value ⁇ A1 as the index that is acquired without involving the compression of the living tissue T of the subject is determined to be abnormal can be used as a trigger of obtaining information for understanding a current condition of the subject.
  • the processor 132 outputs, from the output interface 133, an output control signal OC that causes the output device 14 to output information indicating the estimated CRT.
  • the output device 14 outputs the information visually or audibly based on the output control signal OC.
  • the processor 132 of the processing device 13 having various functions described above may be implemented by at least one non-exclusive microprocessor configured to cooperate with at least one non-exclusive memory.
  • the non-exclusive microprocessor include a CPU, an MPU, and a GPU.
  • the non-exclusive memory include a ROM and a RAM.
  • a computer program for executing the above-described processing may be stored in the ROM.
  • the ROM is an example of a non-transitory computer-readable medium having stored a computer program.
  • the non-exclusive microprocessor designates at least a part of the program stored in the ROM, loads the designated program in the RAM, and executes the above-described processing in cooperation with the RAM.
  • the computer program may be pre-installed in the non-exclusive memory, or may be downloaded from an external server device over a communication network, and then installed in the non-exclusive memory.
  • the external server device is an example of the non-transitory computer-readable medium having stored a computer program.
  • the processor 132 may be implemented by at least one exclusive integrated circuitry capable of executing the above-described computer program, such as a microcontroller, an ASIC, and an FPGA.
  • the above-described computer program is pre-installed in a memory element included in the exclusive integrated circuit.
  • the memory element is an example of the computer-readable medium having stored a computer program.
  • the processor 132 may also be implemented by a combination of the non-exclusive microprocessor and the exclusive integrated circuitry.
  • the first light including 940 nm as the first wavelength ⁇ 1 is used.
  • the first light can be shared with the example described with reference to FIG. 3 wherein the index corresponding to the oxygen saturation of the living tissue T is acquired.
  • the first wavelength ⁇ 1 may be appropriately selected from a wavelength band in which the difference between the absorbance of oxygenated hemoglobin and the absorbance of deoxygenated hemoglobin is relatively small.
  • a wavelength band include 800 nm to 950 nm.
  • the pulse oximeter 10 incorporates the light emitting device 11 and the light detecting device 12. According to the above configuration, the portability of the pulse oximeter capable of acquiring various indices can be enhanced.
  • a pulse oximetry system 20 may be configured.
  • the pulse oximetry system 20 includes a probe 21 and a pulse oximeter 22.
  • the probe 21 and the pulse oximeter 22 are connected to enable communication between them.
  • the pulse oximetry system 20 is an example of the physiological information processing system.
  • the probe 21 is adapted to be attached to the living tissue T of the subject.
  • the probe 21 includes the light emitting device 11 and the light detecting device 12 described with reference to FIG. 1.
  • the pulse oximeter 22 includes the processing device 13 and the output device 14 described with reference to FIG. 1.
  • the processing device 13 is installed in the pulse oximeter.
  • the processing device 13 may be installed in a device capable of performing data communication with the pulse oximeter.
  • the pulse oximeter includes a communication device for communicating data with the processing device 13.
  • the first signal I1 and the second signal I2 outputted from the light detecting device 12 are transmitted to the processing device 13 by the communication device.
  • the processing device 13 executes the above-described various kinds of processing, and transmits an output control signal OC to the pulse oximeter.
  • the pulse oximeter having received the output control signal OC outputs, from the output device 14, information indicating the index as acquired.

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Abstract

A light emitting device emits: first light including a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and second light including a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin. A light detecting device outputs first and second signals respectively corresponding to intensities of the first and second light that have passed through a living tissue. A processing device acquires: a first difference value between light attenuations of the first and second light based on the signals while compression of the living tissue is performed; and a second difference value between the light attenuations based on the signals after the compression is cancelled. A processing device acquires an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first and second difference values.

Description

PHYSIOLOGICAL INFORMATION PROCESSING SYSTEM, PROCESSING DEVICE, AND NON-TRANSITORY COMPUTER-READABLE MEDIUM
The presently disclosed subject matter relates to a system for processing physiological information of a subject. The presently disclosed subject matter also relates to a processing device included in the system, as well as a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in the processing device.
Background
Japanese Patent Publication No. 2021-115640A discloses an apparatus for estimating a capillary refill time (CRT). Specifically, light with a wavelength that is to be absorbed by blood is incident on a living tissue such as a fingertip, and the intensity of the light that has passed through the living tissue is measured. As the living tissue is compressed, blood is eliminated from the living tissue, whereby the intensity of the transmitted light is increased. As the compression is cancelled, the living tissue is refilled with blood, whereby the intensity of the transmitted light is decreased. The CRT is estimated based on a time period from a timing when the compression is cancelled, to a timing when the transmitted light intensity returns to the original level. The CRT is also used as an index reflecting a blood volume in the tissue of the subject.
Summary
It is desired to enable provision of an improved index related to an oxygen saturation of blood contained in a living tissue as well as the blood volume in the tissue, in a simple manner.
A first illustrative aspect of the presently disclosed subject matter may provide a physiological information processing system, comprising:
a light emitting device configured to emit:
first light including a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and
second light including a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin;
a light detecting device configured to output a first signal and a second signal respectively corresponding to an intensity of the first light and an intensity of the second light that have passed through a living tissue of a subject; and
a processing device configured to receive the first signal and the second signal,
wherein the processing device is configured to:
acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
A second illustrative aspect of the presently disclosed subject matter may provide a processing device, comprising:
an interface configured to receive:
a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and
a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin; and
a processor configured to:
acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
A third illustrative aspect of the presently disclosed subject matter may provide a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to:
receive a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin;
receive a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin;
acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
The living tissue includes blood and tissues other than blood. As the blood is eliminated by the compression, the first difference value reflects the light attenuation of the tissues other than the blood. On the other hand, as the blood returns due to the cancellation of the compression, the second difference value reflects both the light attenuation of the blood and the light attenuation of the tissues other than the blood.
Since the oxygen saturation of the blood Tb changes with time, the light attenuation that can be attributed to the blood also changes. However, since the first difference value eliminates the influence of the blood, the value would be constant. On the other hand, the second difference value varies in accordance with the change of the oxygen saturation of the blood. Accordingly, the difference value between the first difference value and the second difference value may be an index that more accurately reflects the change of the oxygen saturation of the blood.
In addition, since the constant first difference value can be handled as a reference value, it is possible to keep monitoring the second difference value as the index once a single compression of the living tissue is performed and then the second difference value is acquired intermittently or continuously.
In order to obtain the above-described advantages, it is not necessary to add a special device or mechanism to the physiological information processing system. Accordingly, it is possible to provide an improved index related to the oxygen saturation of blood contained in the living tissue in a simple manner.
A fourth illustrative aspect of the presently disclosed subject matter may provide a physiological information processing system, comprising:
a light emitting device configured to emit light having a wavelength included in a range from 800nm to 950nm;
a light detecting device configured to output a signal corresponding to an intensity of the light that has passed through a living tissue of a subject; and
a processing device configured to receive the signal,
wherein the processing device is configured to:
acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
A fifth illustrative aspect of the presently disclosed subject matter may provide a processing device, comprising:
an interface configured to receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm; and
a processor configured to:
acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
A sixth illustrative aspect of the presently disclosed subject matter may provide a non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to:
receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm;
acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
The living tissue includes blood and tissues other than blood. As the blood is eliminated by the compression, the first light attenuation reflects the light attenuation of the tissues other than the blood. On the other hand, as the blood returns due to the cancellation of the compression, the second light attenuation reflects both the light attenuation of the blood and the light attenuation of the tissues other than the blood.
Since the blood volume changes with time, the light attenuation that can be attributed to the blood Tb also changes. However, since the first light attenuation eliminates the influence of the blood, the value would be constant. On the other hand, the second light attenuation varies in accordance with the change of the blood volume. Accordingly, the difference value between the first light attenuation and the second light attenuation may be an index that more accurately reflects the volume change of the blood.
In addition, since the constant first light attenuation can be handled as a reference value, it is possible to keep monitoring the second light attenuation as the index once a single compression of the living tissue is performed and then the second light attenuation is acquired intermittently or continuously.
In order to obtain the above-described advantages, it is not necessary to add a special device or mechanism to the physiological information processing system. Accordingly, it is possible to provide an improved index related to the blood volume contained in the living tissue in a simple manner.
FIG. 1 illustrates a functional configuration of a pulse oximeter according to an exemplary embodiment. FIG. 2 is a diagram for explaining processing to be performed by the processing device of FIG. 1. FIG. 3 is a diagram for explaining processing to be performed by the processing device of FIG. 1. FIG. 4 is a diagram for explaining processing to be performed by the processing device of FIG. 1. FIG. 5 illustrates a functional configuration of a photometry system according to another exemplary embodiment.
Exemplary embodiments will be described in detail below with reference to the accompanying drawings. In each of the drawings, the scale is appropriately changed in order to make each element as illustrated have a recognizable size.
FIG. 1 illustrates a functional configuration of a pulse oximeter 10 according to an exemplary embodiment. The pulse oximeter 10 is a device configured to calculate a transcutaneous arterial oxygen saturation (SpO2) of a subject based on a concentration of a light absorber contained in arterial blood of the subject. The pulse oximeter 10 is an example of a physiological information processing system.
The pulse oximeter 10 includes a light emitting device 11. The light emitting device 11 includes a first light emitting element 111 and a second light emitting element 112. The first light emitting element 111 is configured to emit first light including a first wavelength λ1. The second light emitting element 112 is configured to emit second light including the second wavelength λ2.
The first wavelength λ1 is selected as a wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin. Examples of the first wavelength λ1 include 940 nm.
The second wavelength λ2 is selected as a wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin. Examples of the second wavelength λ2 include 660 nm.
Each of the first light emitting element 111 and the second light emitting element 112 may be a semiconductor light emitting element. Examples of the semiconductor light emitting element include a light emitting diode, a laser diode, and an EL element.
The pulse oximeter 10 includes a light detecting device 12. The light detecting device 12 includes a light detecting element. The light detecting element is configured to output a first signal I1 and a second signal I2 respectively corresponding to the intensity of the first light and the intensity of the second light at a light detecting surface. Each of the first signal I1 and the second signal I2 may be an analog signal or a digital signal. Examples of the light detecting element include a photodiode, a phototransistor, and a photoresistor.
The pulse oximeter 10 includes a processing device 13. The processing device 13 includes an input interface 131. The input interface 131 is configured to receive the first signal I1 and the second signal I2 that are outputted from the light detecting device 12. In the case where each of the first signal I1 and the second signal I2 is an analog signal, the input interface 131 is provided with an adequate conversion circuit including an A/D converter. This description is similarly applied to other signals that can be received by the input interface 131 and that will be described later.
The processing device 13 includes a processor 132. The processor 132 is configured to execute processing for implementing various functions described later.
The processing device 13 includes an output interface 133. The output interface 133 is configured to output an emission control signal EC for causing the light emitting device 11 to perform a prescribed light emitting operation. The emission control signal EC may be an analog signal or a digital signal in accordance with the specification of the light emitting device 11. In the case where the emission control signal is an analog signal, the output interface 133 is provided with an adequate conversion circuit including a D/A converter. This description is similarly applied to other signals that can be outputted from the output interface 133 and that will be described later.
Specifically, the processor 132 outputs an emission control signal EC that causes the light emitting device 11 to alternately emit the first light and the second light, from the output interface 133. The first light emitting element 111 and the second light emitting element 112 alternately emit the first light and the second light at a timing specified by the emission control signal EC.
The first light and the second light are alternately incident on a living tissue T of the subject. The first light and the second light that have passed through the living tissue T are alternately incident on the light detecting surface of the light detecting device 12.
Accordingly, the light detecting device 12 alternately outputs the first signal I1 and the second signal I2. The processor 132 of the processing device 13 identifies which signal is received by the input interface 131 based on the timing at which the light emission control of the first light emitting element 111 and the second light emitting element 112 is performed.
The processor 132 is configured to calculate the SpO2 of the subject based on the intensities of the first and second signals I1 and I2.
Specifically, since the intensities of the first light emitted from the first light emitting element 111 and the second light emitted from the second light emitting element 112 are known, a light attenuation A1 of the first light and a light attenuation A2 of the second light in connection with the passage through the living tissue T can be calculated from the intensities of the first light and the second light at the light detecting device 12 that correspond to the first signal I1 and the second signal I2. The SpO2 has a correlation with a ratio of the light attenuation A1 of the first light and the light attenuation A2 of the second light. Accordingly, the value of SpO2 may be calculated by inputting the ratio to a function corresponding to the correlation.
The light attenuation A1 of the first light is expressed by the following equation.

A1 = Ab1 + At1 = Eb1 Hb Db + Zt1 Dt ...(1)

Ab1: a light attenuation of the first light that can be attributed to blood
At1: a light attenuation of the first light that can be attributed to tissues other than the blood
Eb1: an absorbance (dL g-1 cm-1) of the blood with respect to the first light
Hb: a hemoglobin concentration in blood (g dL-1)
Db: a blood thickness (cm)
Zt1: a light attenuation rate (cm-1) of the first light in the tissues other than the blood
Dt: a thickness (cm) of the tissues other than the blood
Similarly, the light attenuation A2 of the second light is expressed by the following equation.

A2 = Ab2 + At2 = Eb2 Hb Db + Zt2 Dt ...(2)

Ab2: a light attenuation of the second light that can be attributed to the blood
At2: a light attenuation of the second light that can be attributed to the tissues other than the blood
Eb2: an absorbance (dL g-1 cm-1) of the blood with respect to the second light
Zt2: a light attenuation rate (cm-1) of the second light in the tissues other than the blood
Since the wavelength dependency of the light attenuation rate with respect to the tissues other than the blood can be estimated to be low, Zt1 = Zt2 can be established. Accordingly, by acquiring a difference value ΔA between the light attenuation A1 of the first light and the light attenuation A2 of the second light, it is possible to eliminate an influence of the tissues other than the blood on the light attenuation.

ΔA = A1 - A2 = Ab1 - Ab2 = (Eb1 - Eb2) Hb Db ...(3)
As the living tissue T is compressed, changes occur in the light attenuation A1 of the first light and the light attenuation A2 of the second light. The compression may be performed with a hand of a user, or may be performed mechanically with an actuator or the like.
FIG. 2 illustrates changes over time of the difference value ΔA that is calculated as described above. As the compression is initiated at a time point t1, blood is eliminated from the living tissue T, whereby the intensities of the first light and the second light as detected increase. Accordingly, the difference value ΔA is increased as well. As the compression is cancelled at a time point t2, blood returns to the living tissue T, whereby the intensities of the first light and the second light as detected decrease. Accordingly, the difference value ΔA is decreased as well.
The processor 132 is configured to acquire, based on the first signal I1 and the second signal I2 that are received by the input interface 131 during the compression of the living tissue T, a difference value between the light attenuation A1 of the first light and the light attenuation A2 of the second light during the compression, as a first difference value ΔAp1. The first difference value ΔAp1 may be acquired as a difference value at an arbitrary time point during a time period from the time point t1 to the time point t2 in FIG. 2, or may be acquired as a statistic value of the difference value at an arbitrary time slot during the time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
The processor 132 is configured to acquire, based on the first signal I1 and the second signal I2 that are received by the input interface 131 after the compression of the living tissue T is cancelled, a difference value between the light attenuation A1 of the first light and the light attenuation A2 of the second light during the compression, as a second difference value ΔAp2. The second difference value ΔAp2 may be acquired as a difference value at an arbitrary time point during a time period after the time point t3 in FIG. 2, or may be acquired as a statistic value of the difference value at an arbitrary time slot during the time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
In order to acquire the first difference value ΔAp1 and the second difference value ΔAp2 at an adequate timing, the processor 132 needs to recognize that the living tissue T is compressed.
In a case where the compression is performed with the hand of the user, the pulse oximeter 10 may notify the user of the timing of the initiation and cancellation of the compression through a notification mechanism (not illustrated). The notification may be performed through at least one of visual notification, audible notification, and haptic notification. The processor 132 may output, from the output interface 133, a control signal that controls the operation of the notification mechanism. The processor 132 may recognize the output timing of the control signal in association with the time period during which the compression is performed.
In a case where the compression is performed with a device such as an actuator (not illustrated), the processor 132 may output, from the output interface 133, a control signal for controlling the operation of the actuator. The processor 132 may recognize the output timing of the control signal in association with the time period during which the compression is performed.
Alternatively, the initiation and cancellation of the compression may be determined in accordance with the fact that a variation of the difference value ΔA as acquired exceeds a threshold.
The processor 132 is configured to subsequently calculate a difference value ΔAb between the first difference value ΔAp1 and the second difference value ΔAp2.

ΔAb = ΔAp2 - ΔAp1 ...(4)
As illustrated in FIG. 3, the living tissue T includes blood Tb and tissues To other than the blood. Since the blood Tb is eliminated by the compression, the first difference value ΔAp1 reflects the light attenuation that can be attributed to the tissues To other than the blood. On the other hand, since the blood Tb returns by the cancellation of the compression, the second difference value ΔAp2 reflects both the light attenuation that can be attributed to the blood Tb and the light attenuation that can be attributed to the tissues To other than the blood.
Since the oxygen saturation of the blood Tb changes with time, the light attenuation that can be attributed to the blood Tb also changes. However, since the first difference value ΔAp1 eliminates the influence of the blood Tb, the value would be constant. On the other hand, the second difference value ΔAp2 varies in accordance with the change of the oxygen saturation of the blood Tb. Accordingly, the difference value ΔAb between the first difference value ΔAp1 and the second difference value ΔAp2 may be an index that more accurately reflects the change of the oxygen saturation of the blood Tb.
In addition, since the constant first difference value ΔAp1 can be handled as a reference value, it is possible to keep monitoring the second difference value ΔAp2 as the index once a single compression of the living tissue T is performed and then the second difference value ΔAp2 is acquired intermittently or continuously.
In order to obtain the above-described advantages, it is not necessary to add a special device or mechanism to the pulse oximeter 10. Accordingly, it is possible to provide an improved index related to the oxygen saturation of blood contained in the living tissue in a simple manner.
As illustrated in FIG. 1, the pulse oximeter 10 may include an output device 14. The processor 132 of the processing device 13 outputs, from the output interface 133, an output control signal OC that causes the output device 14 to output information indicating the difference value ΔAb as the index as acquired.
The output device 14 is configured to output information indicating the difference value ΔAb based on the output control signal OC. The information may be visually provided using at least one of a text, a mark, and a color corresponding to the difference value ΔAb. The visual presentation of the information may be provided as an image that is displayed on a display or projected by a projector, or may be provided as a printed matter. Additionally or alternatively, the information may be audibly provided through a speaker.
Alternatively, the output device 14 may be a data output device that outputs the information to be subjected to processing for acquiring another index or physiological information. The processing may be performed in the pulse oximeter 10, or may be performed in an external device that is independent from the pulse oximeter 10.
As illustrated in FIG. 1, the input interface 131 of the processing device 13 may be configured to receive a measurement signal M corresponding to a measured concentration value of the hemoglobin in blood of the subject from a user interface (not illustrated).
In this case, the processor 132 is configured to acquire the light attenuation A1 of the first light and the light attenuation A2 of the second light based on the measurement signal M.
The value of Hb indicating the hemoglobin concentration in blood that is included in the above-described the equations (1) and (2) is a constant that is commonly used as a statistic value. Technically, however, the actual hemoglobin concentration may have a value different from the constant. The processor 132 according to the present example is configured to use the value of the hemoglobin concentration corresponding to the measurement signal M as the value of Hb in the equations (1) and (2) to acquire the light attenuation A1 of the first light and the light attenuation A2 of the second light.
According to the above configuration, the actual hemoglobin concentration in blood that would be different in accordance with the subject and/or the physical condition can be reflected in the difference value ΔAb that is acquired as the index. Accordingly, the accuracy of the index can be improved.
Next, another exemplary processing performed by the processor 132 of the processing device 13 will be described with reference to FIG. 4. In this example, the processor 132 acquires an index corresponding to the blood volume contained in the living tissue T.
Specifically, the processor 132 acquires a light attenuation A11 of the first light during the compression of the living tissue T, based on the first signal I1 that is received by the input interface 131 during the time period. The light attenuation A11 is an example of a first light attenuation. Since blood is eliminated from the living tissue T during the compression, the light attenuation A11 is substantially expressed by the following equation based on analogy to the equation (1).

A11 = At11 ...(5)

At11: a light attenuation of the first light that can be attributed to the tissues other than the blood during the compression
The light attenuation A11 may be acquired as a value measured at an arbitrary time point during a time period from the time point t1 to the time point t2 in FIG. 2, or may be acquired as a statistic value of values measured at arbitrary time points during that time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
In addition, the processor 132 acquires a light attenuation A12 of the first light after the compression of the living tissue T is cancelled, based on the first signal I1 that is received by the input interface 131during that time period. The light attenuation A12 is an example of a second light attenuation. The light attenuation A12 is expressed by the following equation based on analogy to the equation (1).

A12 = Ab12 + At12 ...(6)

Ab12: a light attenuation of the first light that can be attributed to the blood after the cancellation of the compression
At12: a light attenuation of the first light that can be attributed to the tissues other than the blood after the cancellation of the compression
The light attenuation A12 may be acquired as a value measured at an arbitrary time point that is not earlier than the time point t3 in FIG. 2, or may be acquired as a statistic value of values measured at arbitrary time points during that time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
Subsequently, the processor 132 calculates a difference value ΔA1 between the light attenuation A11 and the light attenuation A12. The difference value ΔA1 is expressed by the following equation.

ΔA1 = A12 - A11 = Ab12 + At12 - At11 ...(7)

Since the light attenuation of the first light that can be attributed to the tissues other than the blood exhibits no substantial change during the compression and after the cancellation of the compression, the difference value ΔA1 substantially represents the light attenuation of the first light that can be attributed to the blood after the cancellation of the compression (ΔA1 is nearly equal to Ab12).
As illustrated in FIG. 4, the living tissue T includes blood Tb and tissues To other than blood. Since the blood Tb is eliminated by the compression, the light attenuation A11 reflects the light attenuation that can be attributed to the tissues To other than the blood. On the other hand, since the blood Tb returns by the cancellation of the compression, the light attenuation A12 reflects both the light attenuation that can be attributed to the blood Tb and the light attenuation that can be attributed to the tissues To other than the blood.
Since the blood volume changes with time, the light attenuation that can be attributed to the blood Tb also changes. However, as illustrated in FIG. 4, since the light attenuation A11 eliminates the influence of the blood Tb, the value would be constant. On the other hand, the light attenuation A12 varies in accordance with a volume change of the blood Tb. Accordingly, the difference value ΔA1 between the light attenuation A11 and the light attenuation A12 may be an index that more accurately reflects the volume change of the blood Tb.
In addition, since the constant light attenuation A11 can be handled as a reference value, it is possible to keep monitoring the light attenuation A12 as the index once a single compression of the living tissue T is performed and then the light attenuation A12 is acquired intermittently or continuously.
In order to obtain the above-described advantages, it is not necessary to add a special device or mechanism to the pulse oximeter 10. Accordingly, it is possible to provide an improved index related to the blood volume contained in the living tissue in a simple manner.
It should be noted that, if such a continuous monitoring is not necessary, the processor 132 may acquire a light attenuation A10 of the first light before the compression of the living tissue T (between the time points t0 and t1 in FIG. 2) based on the first signal I1 that is received by the input interface 131 during that period. The light attenuation A10 is also an example of the second light attenuation. The light attenuation A10 is expressed by the following equation.

A10 = Ab10 + At10 ...(8)

Ab10: a light attenuation of the first light that can be attributed to the blood before the compression
At10: a light attenuation of the first light that can be attributed to the tissues other than the blood before the compression
The light attenuation A10 may be acquired as a measured value at an arbitrary time point during a time period from the time point t0 to the time point t1 in FIG. 2, or may be acquired as a statistic value of the measured value at an arbitrary time period during the time period. Examples of the statistic value include a mean value, an intermediate value, and a mode value.
Subsequently, the processor 132 calculates a difference value ΔA1’ between the light attenuation A10 and the light attenuation A11. The difference value ΔA1’ is expressed by the following equation.

ΔA1’ = A10 - A11 = Ab10 + At10 - A11 ...(9)

Since the light attenuation of the first light that can be attributed to the tissues other than the blood exhibits no substantial change before and during the compression, the difference value ΔA1 substantially represents the light attenuation of the first light that can be attributed to the blood after the cancellation of the compression (ΔA1’ is nearly equal to Ab12). Accordingly, the difference value ΔA1’ may also be an index corresponding to the blood volume contained in the living tissue T.
In this example, the processor 132 may be configured to acquire the light attenuation A12 based on the measurement signal M illustrated in FIG. 1. Similarly to the example described with reference to the equation (1), the processor 132 is configured to use the value of the hemoglobin concentration corresponding to the measurement signal M as the value of Hb that can be included in the term of A12 in the equation (6) to acquire the light attenuation A12.
According to the above configuration, the actual hemoglobin concentration in blood that would be different in accordance with the subject and/or the physical condition can be reflected in the difference value ΔA1 that is acquired as the index. Accordingly, the accuracy of the index can be improved.
As the compression of the living tissue T that is performed in order to acquire the above-described difference value ΔA1 is cancelled, a capillary refill time (CRT) of the living tissue T can be specified based on the changes with time of the difference value ΔA as illustrated in FIG. 2. Specifically, the CRT is specified as a time period from the time point t2 when the compression is cancelled, to the time point t3 when the transmitted light intensity can be regarded as returning to the original level. The difference value ΔA1 and the CRT that are acquired with the compression of the living tissue T are referred to as a reference difference value ΔA1r, and a reference CRT (rCRT).

eCRT = (ΔA1r / ΔA1) rCRT
The processor 132 may be configured to estimate a value of the CRT based on the difference value ΔA1 as the index that is continuously acquired after the compression of the living tissue T. Specifically, an estimated value (eCRT) of the CRT is calculated by the following equation.
According to the above configuration, it is possible to keep monitoring the estimated value of the CRT once a single compression of the living tissue T is performed and then the difference value ΔA1 is acquired intermittently or continuously. In other words, the monitoring of the estimated value of the CRT can be continued without repeating the compression of the living tissue T.
The processor 132 may be configured to cause the pulse oximeter 10 to perform a notification prompting the acquisition of specific physiological information based on the difference value ΔA1 as the index that is acquired as described above. For example, in response to a determination that that the difference value ΔA1 as acquired is not within a prescribed threshold range, a notification prompting reacquisition of the CRT involving the compression of the living tissue T may be performed.
According to the above configuration, the fact that the difference value ΔA1 as the index that is acquired without involving the compression of the living tissue T of the subject is determined to be abnormal can be used as a trigger of obtaining information for understanding a current condition of the subject.
In this case, the processor 132 outputs, from the output interface 133, an output control signal OC that causes the output device 14 to output information indicating the estimated CRT. The output device 14 outputs the information visually or audibly based on the output control signal OC.
The processor 132 of the processing device 13 having various functions described above may be implemented by at least one non-exclusive microprocessor configured to cooperate with at least one non-exclusive memory. Examples of the non-exclusive microprocessor include a CPU, an MPU, and a GPU. Examples of the non-exclusive memory include a ROM and a RAM. In this case, a computer program for executing the above-described processing may be stored in the ROM. The ROM is an example of a non-transitory computer-readable medium having stored a computer program. The non-exclusive microprocessor designates at least a part of the program stored in the ROM, loads the designated program in the RAM, and executes the above-described processing in cooperation with the RAM. The computer program may be pre-installed in the non-exclusive memory, or may be downloaded from an external server device over a communication network, and then installed in the non-exclusive memory. In this case, the external server device is an example of the non-transitory computer-readable medium having stored a computer program.
The processor 132 may be implemented by at least one exclusive integrated circuitry capable of executing the above-described computer program, such as a microcontroller, an ASIC, and an FPGA. In this case, the above-described computer program is pre-installed in a memory element included in the exclusive integrated circuit. The memory element is an example of the computer-readable medium having stored a computer program. The processor 132 may also be implemented by a combination of the non-exclusive microprocessor and the exclusive integrated circuitry.
Each of the configurations exemplified above is merely illustrative for facilitating understanding of the presently disclosed subject matter. Each exemplary configuration may be appropriately modified or combined with another exemplary configuration within the scope of the presently disclosed subject matter.
In the example described with reference to FIG. 4 wherein the index corresponding to the blood volume contained in the living tissue T is acquired, the first light including 940 nm as the first wavelength λ1 is used. According to the above configuration, the first light can be shared with the example described with reference to FIG. 3 wherein the index corresponding to the oxygen saturation of the living tissue T is acquired.
However, particularly in a case where only the index corresponding to the blood volume is necessary to be acquired, the first wavelength λ1 may be appropriately selected from a wavelength band in which the difference between the absorbance of oxygenated hemoglobin and the absorbance of deoxygenated hemoglobin is relatively small. Examples of such a wavelength band include 800 nm to 950 nm.
In the above exemplary embodiment, the pulse oximeter 10 incorporates the light emitting device 11 and the light detecting device 12. According to the above configuration, the portability of the pulse oximeter capable of acquiring various indices can be enhanced.
However, as illustrated in FIG. 5, a pulse oximetry system 20 may be configured. The pulse oximetry system 20 includes a probe 21 and a pulse oximeter 22. The probe 21 and the pulse oximeter 22 are connected to enable communication between them. The pulse oximetry system 20 is an example of the physiological information processing system.
The probe 21 is adapted to be attached to the living tissue T of the subject. The probe 21 includes the light emitting device 11 and the light detecting device 12 described with reference to FIG. 1. The pulse oximeter 22 includes the processing device 13 and the output device 14 described with reference to FIG. 1.
In each of the above-described exemplary embodiments, the processing device 13 is installed in the pulse oximeter. However, the processing device 13 may be installed in a device capable of performing data communication with the pulse oximeter. In this case, the pulse oximeter includes a communication device for communicating data with the processing device 13. The first signal I1 and the second signal I2 outputted from the light detecting device 12 are transmitted to the processing device 13 by the communication device. The processing device 13 executes the above-described various kinds of processing, and transmits an output control signal OC to the pulse oximeter. The pulse oximeter having received the output control signal OC outputs, from the output device 14, information indicating the index as acquired.
The present application is based on Japanese Patent Application No. 2024-112558 filed on July 12, 2024, the entire contents of which are hereby incorporated by reference.

Claims (10)

  1. A physiological information processing system, comprising:
    a light emitting device configured to emit:
    first light including a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and
    second light including a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin;
    a light detecting device configured to output a first signal and a second signal respectively corresponding to an intensity of the first light and an intensity of the second light that have passed through a living tissue of a subject; and
    a processing device configured to receive the first signal and the second signal,
    wherein the processing device is configured to:
    acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
    acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
  2. The physiological information processing system according to claim 1,
    wherein the processing device is configured to:
    receive a measurement signal corresponding to a hemoglobin concentration in blood measured for the subject; and
    acquire the light attenuation of the first light and the light attenuation of the second light based on the measurement signal.
  3. A physiological information processing system, comprising:
    a light emitting device configured to emit light having a wavelength included in a range from 800nm to 950nm;
    a light detecting device configured to output a signal corresponding to an intensity of the light that has passed through a living tissue of a subject; and
    a processing device configured to receive the signal,
    wherein the processing device is configured to:
    acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
    acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
  4. The physiological information processing system according to claim 3,
    wherein the processing device is configured to:
    receive a measurement signal corresponding to a hemoglobin concentration in blood measured for the subject; and
    correct the index based on the measurement signal.
  5. The physiological information processing system according to claim 3 or 4,
    wherein the processing device is configured to estimate a capillary refill time of the living tissue based on the index.
  6. The physiological information processing system according to any one of claims 3 to 5,
    wherein the processing device is configured to determine, based on the index, whether particular physiological information is necessary to be acquired from the subject.
  7. A processing device, comprising:
    an interface configured to receive:
    a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin; and
    a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin; and
    a processor configured to:
    acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
    acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
  8. A non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to:
    receive a first signal corresponding to an intensity of first light having passed a living tissue of a subject and having a first wavelength at which an absorbance of oxygenated hemoglobin is larger than an absorbance of deoxygenated hemoglobin;
    receive a second signal corresponding to an intensity of second light having passed the living tissue and having a second wavelength at which the absorbance of deoxygenated hemoglobin is larger than the absorbance of oxygenated hemoglobin;
    acquire a first difference value between a light attenuation of the first light and a light attenuation of the second light based on the first signal and the second signal while compression of the living tissue is performed;
    acquire a second difference value between the light attenuation of the first light and the light attenuation of the second light based on the first signal and the second signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to an oxygen saturation of blood contained in the living tissue based on a difference between the first difference value and the second difference value.
  9. A processing device, comprising:
    an interface configured to receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm; and
    a processor configured to:
    acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
    acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
  10. A non-transitory computer-readable medium having stored a computer program adapted to be executed by a processor installed in a processing device, the computer program being configured to, when executed, cause the processing device to:
    receive a signal corresponding to an intensity of light having passed a living tissue of a subject and having a wavelength included in a range from 800nm to 950nm;
    acquire a first light attenuation of the light based on the signal while compression of the living tissue is performed;
    acquire a second light attenuation of the light based on the signal after the compression of the living tissue is cancelled; and
    acquire an index corresponding to a blood volume contained in the living tissue based on a difference between the first difference value and the second difference value.
PCT/JP2025/024227 2024-07-12 2025-07-04 Physiological information processing system, processing device, and non-transitory computer-readable medium Pending WO2026014387A1 (en)

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JP2024-112558 2024-07-12
JP2024112558A JP2026011724A (en) 2024-07-12 2024-07-12 Biological information processing system, processing device, and computer program

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JP2021115640A (en) 2020-01-23 2021-08-10 株式会社トップ通商 Hook separation preventing metal fitting for tool fall preventing device and its using method
US20220338767A1 (en) * 2019-07-02 2022-10-27 Nihon Kohden Corporation Medical photometer
US20230048928A1 (en) * 2021-08-10 2023-02-16 Nihon Kohden Corporation Pulse oximeter, pulse oximetry system, processing device, and pulse oximetry method
JP2024112558A (en) 2023-02-08 2024-08-21 三菱電機ビルソリューションズ株式会社 Removal aid

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013118978A (en) * 2011-12-08 2013-06-17 Sony Corp Measuring device, measuring method, program and recording medium
US20140213865A1 (en) * 2013-01-31 2014-07-31 Nihon Kohden Corporation Biological signal measuring system and biological signal measuring apparatus
US20220338767A1 (en) * 2019-07-02 2022-10-27 Nihon Kohden Corporation Medical photometer
JP2021115640A (en) 2020-01-23 2021-08-10 株式会社トップ通商 Hook separation preventing metal fitting for tool fall preventing device and its using method
US20230048928A1 (en) * 2021-08-10 2023-02-16 Nihon Kohden Corporation Pulse oximeter, pulse oximetry system, processing device, and pulse oximetry method
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