Pulse oximeter, pulse oximetry system, processing device, and pulse oximetry method

Abstract

To enhance convenience of a pulse oximeter capable of estimating a capillary vessel re-filling time.SOLUTION: A light emitting device 11 emits a first light including a first wavelength λ1 and a second light including a second wavelength λ2 different from the first wavelength λ1. A light receiving device 12 outputs a first detection signal I1 and a second detection signal I2 corresponding to the intensity of the first light and the intensity of the second light respectively after the interaction with a tissue T of a subject. A processing device 13 calculates a pulsation rate of at least one of the first detection signal I1 and the second detection signal I2, calculates percutaneous arterial oxygen saturation of the subject on the basis of the first detection signal I1 and the second detection signal I2, and estimates a capillary vessel re-filling time of the tissue T on the basis of the time that at least one of the pulsation rate that has changed accompanying the oppression of the tissue T and the percutaneous arterial oxygen saturation returns within a predetermined threshold range as compared to each value before the oppression. An output device 14 outputs information indicating the capillary vessel re-filling time.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pulse oximeter and pulse oximetry method capable of estimating capillary refill time (CRT), as well as to a processing device and pulse oximetry system that may be used with the pulse oximeter. [Background technology]

[0002] CRT measurements are used in the field of emergency medicine to determine the need for infusions and priorities in triage (identification of emergencies). Specifically, a medical professional applies pressure to the subject's biological tissue, such as the fingertip, and visually checks the change in skin color after the pressure is released. If the original color returns within two seconds, the condition is deemed normal. However, the method of applying pressure to biological tissue with the hand and visually checking the change in skin color lacks quantitativeness and is prone to errors caused by the person taking the measurements.

[0003] It has therefore been proposed to use a pulse oximeter to estimate CRT (see, for example, Patent Document 1). Specifically, light with a wavelength that is absorbed by blood is incident on biological tissue such as a fingertip, and the intensity of the light transmitted through the biological tissue is measured. Pressure removes blood from the biological tissue at that location, so the intensity of the transmitted light increases. When pressure is released, blood refills the biological tissue at that location, so the intensity of the transmitted light decreases. CRT is estimated based on the time it takes for the transmitted light intensity to return to its original level after pressure is released. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-115640 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to improve the convenience of a pulse oximeter capable of estimating capillary refill time. [Means for solving the problem]

[0006] In order to achieve the above object, a first aspect of the present invention is a pulse oximeter comprising: a light emitting device that emits a first light having a first wavelength and a second light having a second wavelength different from the first wavelength; a light receiving device that outputs a first signal and a second signal corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of a subject; a processing device that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and estimates a capillary refill time of the tissue based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range with respect to the respective values ​​before compression; an output device for outputting information indicative of the capillary refill time; It is equipped with:

[0007] A second aspect that can be provided to achieve the above object is a pulse oximetry system, comprising: a light emitting device that emits a first light having a first wavelength and a second light having a second wavelength different from the first wavelength; a light receiving device that outputs a first signal and a second signal corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of a subject; a pulse oximeter that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and outputs information indicating a capillary refill time of the tissue estimated based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range with respect to the respective values ​​before compression; It is equipped with:

[0008] A third aspect that can be provided to achieve the above object is a processing device, comprising: an interface that receives a first signal and a second signal corresponding to an intensity of a first light having a first wavelength and an intensity of a second light having a second wavelength different from the first wavelength, respectively, after being emitted from the light-emitting unit and interacting with tissue of a subject; a processor that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and estimates a capillary refill time of the tissue based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range relative to their respective values ​​before compression; It is equipped with:

[0009] A fourth aspect that can be provided to achieve the above object is a pulse oximetry method, comprising: Emitting a first light having a first wavelength and a second light having a second wavelength different from the first wavelength to a light emitting unit; receiving a first signal and a second signal from the light receiving unit corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of the subject; Calculating a pulsation rate of at least one of the first signal and the second signal; Calculating a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal; The capillary refill time of the tissue is estimated based on the time it takes for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range relative to their respective values ​​before compression.

[0010] According to the configurations of the above aspects, the capillary refill time of the subject can be estimated by a simple process of monitoring the value of the percutaneous arterial oxygen saturation of the subject obtained by the inherent function of the pulse oximeter and the change over time in the value of the pulsation rate of at least one of the first signal and the second signal used to calculate the percutaneous arterial oxygen saturation. This can significantly reduce the computation load of a processing device used together with the pulse oximeter. In other words, the required computing power can be reduced, so that the processing device can be made smaller and simpler while still being able to specify the capillary refill time. When the processing device is mounted on the pulse oximeter, the size and complexity of the pulse oximeter can be suppressed. Therefore, the convenience of the pulse oximeter capable of estimating the capillary refill time can be improved. [Brief description of the drawings]

[0011] [Figure 1] 2 illustrates a functional configuration of a pulse oximeter according to an embodiment. [Diagram 2] 2 illustrates the change over time in intensity of a first detection signal in FIG. 1; [Diagram 3] 2 illustrates an example of a process flow executed by the processing device of FIG. 1. [Figure 4] 1 illustrates a functional configuration of a pulse oximetry system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Note that the scale of each of the drawings referred to in the following description is appropriately changed so that each element can be recognized.

[0013] 1 illustrates a functional configuration of a pulse oximeter 10 according to one embodiment. The pulse oximeter 10 is a device that calculates the percutaneous arterial oxygen saturation (SpO2) of a subject based on the concentration of a light-absorbing substance contained in the subject's arterial blood.

[0014] The pulse oximeter 10 includes a light emitting device 11, a light receiving device 12, a processing device 13, and an output device 14.

[0015] 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 a first light having a first wavelength λ1. The second light emitting element 112 is configured to emit a second light having a second wavelength λ2.

[0016] The first wavelength λ1 and the second wavelength λ2 are selected as two wavelengths at which a significant difference is observed in the absorbance of the target light-absorbing substance in blood. In this example, the first wavelength λ1 and the second wavelength λ2 are selected based on the absorption characteristics of hemoglobin required for calculating SpO2. For example, the first wavelength λ1 may be included in the infrared wavelength band, and the second wavelength λ2 may be included in the red wavelength band.

[0017] 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.

[0018] The light receiving device 12 includes a light receiving element. The light receiving element is configured to output a first detection signal I1 and a second detection signal I2 corresponding to the intensity of the first light and the intensity of the second light incident on the light receiving surface, respectively. Each of the first detection signal I1 and the second detection signal I2 may be an analog signal or a digital signal. Examples of the light receiving element include a photodiode, a phototransistor, and a photoresistor.

[0019] The processing device 13 includes an input interface 131. The input interface 131 is configured to receive the first detection signal I1 and the second detection signal I2 output from the light receiving device 12. When each of the first detection signal I1 and the second detection signal I2 is an analog signal, the input interface 131 includes an appropriate conversion circuit including an A / D converter.

[0020] The processing device 13 includes a processor 132. The processor 132 is configured to execute processes for realizing various functions described below.

[0021] The processor 132 may be realized by a general-purpose microprocessor that operates in cooperation with a general-purpose memory. Examples of the general-purpose microprocessor include a CPU, an MPU, and a GPU. Examples of the general-purpose memory include a ROM and a RAM. In this case, the ROM may store a computer program that executes the above-mentioned processing. The general-purpose microprocessor specifies at least a part of the computer program stored in the ROM, expands it on the RAM, and executes the above-mentioned processing in cooperation with the RAM.

[0022] The processor 132 may be realized by a dedicated integrated circuit capable of executing the above computer program, such as a microcontroller, an ASIC, or an FPGA. In this case, the above computer program is pre-installed in a memory element included in the dedicated integrated circuit. The processor 32 may be realized by a combination of a general-purpose microprocessor and a dedicated integrated circuit.

[0023] The processing device 13 includes an output interface 133. The output interface 133 is configured to output a control signal for causing the light-emitting device 11 and the output device 14 to perform a predetermined operation. The control signal may be an analog signal or a digital signal. When the control signal is an analog signal, the output interface 133 includes an appropriate conversion circuit including a D / A converter.

[0024] Specifically, the processor 132 outputs a light emission control signal EC for causing 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 designated by the light emission control signal EC.

[0025] The first light and the second light are alternately incident on the subject's tissue T. The first light and the second light that have interacted with the tissue T are incident on the light receiving surface of the light receiving element. The expression "light that has interacted with the tissue" as used in this specification encompasses both light that has passed through the tissue and light that has been reflected by the tissue.

[0026] Therefore, the light receiving device 12 alternately outputs the first detection signal I1 and the second detection signal I2. The processor 132 of the processing device 13 identifies which detection signal has been 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.

[0027] The processor 132 is configured to calculate a pulsation rate of the first detection signal I1 based on the change over time in the intensity of the first detection signal I1. The pulsation rate is calculated as a ratio of an AC component to a DC component of the intensity of the first detection signal I1.

[0028] That is, the pulsation rate is calculated based on the first detection signal I1 corresponding to the received light intensity of the infrared light at the light receiving device 12. This is because the difference in the absorption characteristics of infrared light between oxygenated hemoglobin and deoxygenated hemoglobin is small, and the pulsation rate is less affected by changes in SpO2. However, the pulsation rate may be calculated based on the second detection signal I2 depending on the situation, or the pulsation rate may be calculated for both the first detection signal I1 and the second detection signal I2 and the one with the better conditions may be selected.

[0029] In addition, the processor 132 is configured to calculate the subject's SpO2 based on the intensity of the first detection signal I1 and the intensity of the second detection signal I2.

[0030] Since the intensity of the first light emitted from the first light emitting element 111 and the intensity of the second light emitted from the second light emitting element 112 are known, the attenuation of the first light and the attenuation of the second light as a result of the interaction with the tissue T can be calculated from the received intensities of the first light and the second light in the light receiving device 12 corresponding to the first detection signal I1 and the second detection signal I2. SpO2 is correlated with the ratio of the attenuation of the first light to the attenuation of the second light. Therefore, the value of SpO2 can be calculated by inputting the ratio into a function corresponding to the correlation.

[0031] When the tissue T of the subject to which the first light and the second light are irradiated is compressed, the attenuation of the first light and the attenuation of the second light change. The compression may be performed by the user's hand, or may be performed mechanically by an actuator or the like.

[0032] 2 illustrates an example of a change over time in the received light intensity of the first light corresponding to the first detection signal I1. When compression begins at time t1, blood is expelled from the tissue T, and the received light intensity increases. Accordingly, the pulsation rate and SpO2 also change. When compression is released at time t2, blood returns to the tissue T, and the received light intensity decreases. Accordingly, the pulsation rate and SpO2 also approach the values ​​before compression began.

[0033] Processor 132 is configured to determine the time from time t2 when compressions are released until both the pulsation rate value and the SpO2 value return to within a predetermined threshold range of their values ​​before compressions began. Figure 2 shows an example where, at time t3, both the pulsation rate value and the SpO2 value have returned to within a predetermined threshold range of their values ​​before compressions began.

[0034] The processor 132 is configured to estimate the time from time t2 to time t3 as a capillary refill time (CRT) of the tissue T. As illustrated in Fig. 1, the processor 132 outputs an output control signal OC from the output interface 133 to cause the output device 14 to output information indicating the estimated CRT.

[0035] The output device 14 is configured to output information indicative of the estimated CRT based on the output control signal OC. The information may be provided visually using at least one of text, a mark, and a color corresponding to the CRT. The visual presentation of the information may be provided as an image displayed on a display or may be provided as a printed matter. Additionally or alternatively, the information may be provided audibly through a speaker.

[0036] FIG. 3 illustrates an example of the flow of processing executed by the processor 132 of the processing device 13 configured as described above.

[0037] First, the processor 132 determines whether compression of the subject's tissue T has started (STEP 1). For example, the processor 132 may be configured to monitor a time moving average value of the intensity of the first detection signal I1 received by the input interface 131. The processor 132 determines that compression of the tissue T has started when the increase amount per unit time of this time moving average value exceeds a threshold value. The process is repeated until it is determined that compression of the tissue T has started (NO in STEP 1).

[0038] When it is determined that compression of the tissue T has begun (YES in STEP 1), the pulsation rate value of the first detection signal I1 calculated at that point in time or a predetermined time before that point in time and the subject's SpO2 value are stored as reference values ​​(STEP 2).

[0039] Next, the processor 132 determines whether the pressure on the tissue T has been released (STEP 3). For example, the processor 132 determines that the pressure on the tissue T has been released when the amount of decrease per unit time of the time moving average value of the intensity of the first detection signal I1 exceeds a threshold. The process is repeated until it is determined that the pressure on the tissue T has been released (NO in STEP 3).

[0040] When it is determined that compression of tissue T has started (YES in STEP 3), processor 132 determines whether the difference between each of the calculated pulsation rate value and SpO2 value and the respective reference values ​​stored in STEP 2 is less than the threshold value (STEP 4). In other words, it is determined whether the pulsation rate and SpO2 that have changed with compression have returned to a predetermined threshold range with respect to the respective values ​​before compression. This process is repeated until it is determined that the difference between the pulsation rate value and its reference value is less than the threshold value and that the difference between the SpO2 value and its reference value is less than the threshold value (NO in STEP 4).

[0041] If it is determined that the difference between the pulsation rate value and its reference value is less than the threshold value and the difference between the SpO2 value and its reference value is less than the threshold value (YES in STEP 4), processor 132 estimates the time from the point at which it is determined in STEP 3 that compression on tissue T has been released to the point at which it is determined in STEP 4 that the difference from each reference value is less than the threshold value as the subject's CRT (STEP 5).

[0042] Next, the processor 132 outputs an output control signal OC, which causes the output device 14 to output information indicating the estimated CRT, from the output interface 133 (STEP 6).

[0043] According to the above-mentioned configuration, the CRT of the subject can be estimated by a simple process of monitoring the change over time in the value of the SpO2 of the subject acquired by the inherent function of the pulse oximeter 10 and the value of the pulsation rate of the first detection signal I1 used to calculate the SpO2. This significantly reduces the computation load on the processing device 13 mounted on the pulse oximeter 10. In other words, the required computational power can be lowered, so that the processing device 13 can be made smaller and simpler while still being able to identify the CRT. As a result, the size and complexity of the pulse oximeter 10 can be suppressed. This improves the convenience of the pulse oximeter capable of estimating the CRT.

[0044] 1, the pulse oximeter 10 may include an alarm device 15. The alarm device 15 is configured to provide an alarm that suggests a possible change in the hemodynamics of the subject. The alarm may be provided through at least one of a visual alarm, an audio alarm, and a tactile alarm.

[0045] In this case, the processor 132 of the processing device 13 is configured to output an alarm control signal NC from the output interface 133 to cause the alarm device 15 to make the above-mentioned alarm when the pulsation rate of the first detection signal I1 that has changed due to compression of the tissue T and the time it takes for the subject's SpO2 to return to within a predetermined threshold range for each value before compression exceed a threshold value.

[0046] Specifically, as illustrated in FIG. 3, if it is determined that the pulsation rate and SpO2 that have changed due to compression have not returned to within a predetermined threshold range relative to their respective values ​​before compression (NO in STEP 4), processor 132 determines whether a predetermined length of time has elapsed since it was determined in STEP 3 that compression on tissue T was released (STEP 7).

[0047] If it is determined that the predetermined length of time has not elapsed (NO in STEP 7), the process returns to STEP 4. If it is determined that the predetermined length of time has elapsed (YES in STEP 7), the processor 132 outputs, from the output interface 133, a notification control signal NC that causes the notification device 15 to issue a notification suggesting a possible change in the subject's circulatory dynamics (STEP 8).

[0048] If there is no significant change in the subject's circulatory dynamics before and after compression of the tissue T, the pulsation rate value and the SpO2 value will return to their pre-compression values ​​within a reasonable time after the compression is released. In other words, if the pulsation rate value and the SpO2 value do not return to their pre-compression values ​​within a reasonable time after the compression is released, some change in the subject's circulatory dynamics is suspected. With the above configuration, the possibility that such a situation has occurred can be notified to the user by simple processing. Therefore, the convenience of the pulse oximeter capable of estimating CRT can be further improved.

[0049] 1, the pulse oximeter 10 may further include a temperature detection device 16. The temperature detection device 16 includes a temperature sensor for detecting the temperature of tissue T of the subject. The temperature detection device 16 is configured to output a temperature detection signal TD corresponding to the temperature. The temperature detection signal TD may be an analog signal or a digital signal.

[0050] In this case, the input interface 131 of the processing device 13 is configured to be able to also accept the temperature detection signal TD. When the temperature detection signal TD is an analog signal, the input interface 131 includes an appropriate conversion circuit including an A / D converter.

[0051] The processor 132 of the processing device 13 is configured to determine whether the temperature of the tissue T is below a threshold value based on the temperature detection signal TD received by the input interface 131. When the processor 132 determines that the temperature of the tissue T is below the threshold value, the processor 132 is configured to output, from the output interface 133, a notification control signal NC for causing the notification device 15 to issue a notification suggesting that the reliability of the estimated CRT may be low.

[0052] When the temperature of the subject's tissue T is low, blood circulation is reduced, and the time it takes for blood to return to the tissue T after the pressure is released tends to be longer. In this case, the estimated CRT value may be longer than the CRT value that should be obtained for the subject. With the above configuration, such a situation can be notified to the user, providing an opportunity to check the estimated CRT value. Therefore, the convenience of the pulse oximeter capable of estimating CRT can be further improved.

[0053] In addition, the processor 132 may be configured to determine whether the estimated CRT value exceeds a threshold. In addition to or instead of the above-mentioned notification regarding the reliability of the estimated CRT, the processor 132 is configured to output, from the output interface 133, a notification control signal NC for causing the notification device 15 to issue a notification indicating that the subject may have hypothermia, when the processor 132 determines that the temperature of the tissue T is below the threshold and the estimated CRT value exceeds the threshold.

[0054] If the subject has hypothermia, the time it takes for blood to return to the tissue T after pressure is released tends to be longer. Therefore, if the estimated CRT is too long, hypothermia is suspected for the subject. With the above-described configuration, such a situation can be notified to the user, providing an opportunity to check the subject's condition. Therefore, the convenience of the pulse oximeter capable of estimating CRT can be further improved.

[0055] The above-described embodiment is merely an example for facilitating understanding of the present invention. The configurations according to the above-described embodiment may be appropriately modified or improved without departing from the spirit and scope of the present invention.

[0056] In the above embodiment, the processing device 13 estimates the CRT of the tissue T based on the time until the pulsation rate calculated for at least one of the first detection signal I1 and the second detection signal I2 and the SpO2 calculated for the subject return to within a predetermined threshold range with respect to each value before compression. However, the processing device 13 may estimate the CRT of the tissue T based on the time until at least one of the pulsation rate and the SpO2 returns to within a predetermined threshold range with respect to the value before compression.

[0057] In each of the above-described embodiments, the pulse oximeter 10 includes the light-emitting device 11, the light-receiving device 12, and the temperature detection device 16. This configuration can improve the portability of the pulse oximeter capable of estimating the CRT. The effect of reducing the computational load of the processing device 13 can also contribute to improving the portability.

[0058] However, the pulse oximetry system 20 may be configured as illustrated in Fig. 4. The pulse oximetry system 20 includes a probe 21 and a pulse oximeter 22. The probe 21 and the pulse oximeter 22 are communicatively connected.

[0059] The probe 21 is configured to be attachable to tissue T of a subject. The probe 21 includes the light emitting device 11 and the light receiving device 12 described with reference to Fig. 1. The probe 21 may include the temperature detecting device 16 described with reference to Fig. 1, if necessary.

[0060] The pulse oximeter 22 includes the processing device 13 and the output device 14 described with reference to Fig. 1. The pulse oximeter 22 may include the notification device 15 described with reference to Fig. 1, if necessary.

[0061] In each of the examples described so far, the processing device 13 is mounted on a pulse oximeter. However, the processing device 13 may be mounted on a device capable of data communication with the pulse oximeter. In this case, the pulse oximeter includes a communication device for data communication with the processing device 13. The first detection signal I1 and the second detection signal I2 output from the light receiving device 12 are transmitted to the processing device 13 by the communication device. The processing device 13 executes the various processes described above and transmits an output control signal OC to the pulse oximeter. The pulse oximeter that receives the output control signal OC outputs information indicating the calculated SpO2 and the estimated CRT from the output device 14.

[0062] The expression "at least one of A and B" used in this specification with respect to two entities A and B includes the cases where only A is specified, only B is specified, and both A and B are specified. Each entity A and B may be singular or plural unless otherwise specified.

[0063] The expression "at least one of A, B, and C" used in this specification with respect to three entities A, B, and C means a case where only A is specified, a case where only B is specified, a case where only C is specified, a case where A and B are specified, a case where B and C are specified, a case where A and C are specified, and a case where all of A, B, and C are specified. Each of the entities A, B, and C may be singular or plural unless otherwise specified. The same applies to a case where the number of entities to be described is four or more. [Explanation of symbols]

[0064] 10: pulse oximeter, 11: light emitting device, 12: light receiving device, 13: processing device, 131: input interface, 132: processor, 133: output interface, 14: output device, 15: notification device, 16: temperature detection device, 20: pulse oximetry system, 22: pulse oximeter, I1: first detection signal, I2: second detection signal, T: tissue, λ1: first wavelength, λ2: second wavelength

Claims

1. a light emitting device that emits a first light having a first wavelength and a second light having a second wavelength different from the first wavelength; a light receiving device that outputs a first signal and a second signal corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of a subject; a processing device that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and estimates a capillary refill time of the tissue based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range with respect to the respective values ​​before compression; an output device for outputting information indicative of the capillary refill time; Equipped with Pulse oximeter.

2. and a notification device that issues a notification indicating a possibility of a change in the circulatory dynamics of the subject when the time exceeds a threshold value.

2. The pulse oximeter of claim 1.

3. a temperature detection device for detecting a temperature of the tissue; an alarm for indicating that the capillary refill time may be unreliable if the temperature is below a threshold; Equipped with 3. The pulse oximeter according to claim 1 or 2.

4. a temperature detection device for detecting a temperature of the tissue; an alarm device that issues an alarm indicating that the subject may be suffering from hypothermia if the temperature falls below a threshold and the capillary refill time exceeds a threshold; Equipped with 4. A pulse oximeter according to any one of claims 1 to 3.

5. a light emitting device that emits a first light having a first wavelength and a second light having a second wavelength different from the first wavelength; a light receiving device that outputs a first signal and a second signal corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of a subject; a pulse oximeter that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and outputs information indicating a capillary refill time of the tissue estimated based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range with respect to the respective values ​​before compression; Equipped with Pulse oximetry system.

6. an interface that receives a first signal and a second signal corresponding to an intensity of a first light having a first wavelength and an intensity of a second light having a second wavelength different from the first wavelength, respectively, after being emitted from the light-emitting unit and interacting with tissue of a subject; a processor that calculates a pulsation rate of at least one of the first signal and the second signal, calculates a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal, and estimates a capillary refill time of the tissue based on a time required for at least one of the pulsation rate and the percutaneous arterial oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range relative to their respective values ​​before compression; Equipped with Processing unit.

7. A processing device according to claim 6 ; an output device for outputting information indicative of the capillary refill time; A pulse oximeter.

8. Emitting a first light having a first wavelength and a second light having a second wavelength different from the first wavelength to a light emitting unit; receiving a first signal and a second signal from the light receiving unit corresponding to the intensity of the first light and the intensity of the second light, respectively, after interacting with tissue of the subject; Calculating a pulsation rate of at least one of the first signal and the second signal; Calculating a percutaneous arterial oxygen saturation of the subject based on the first signal and the second signal; A capillary refill time of the tissue is estimated based on a time required for at least one of the pulsation rate and the percutaneous arterial blood oxygen saturation, which have changed due to compression of the tissue, to return to within a predetermined threshold range with respect to the respective values ​​before compression. Pulse oximetry methods.

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