Medical Photometer

Abstract

To enable at least either a clinical condition or physiological condition of a biological tissue of a subject to be presumed using the principle of photometry.SOLUTION: An input interface 41 receives a signal S1 corresponding to intensity of light that passes through a biological tissue of a subject. A compression control unit 44 controls compression operation performed by a compression device 30 worn by a subject body to changes at least one of thickness of the biological tissue, an amount of blood included in the biological tissue, an amount of intercellular fluid included in the biological tissue, an amount of the blood flown into the biological tissue, and an amount of blood flown out from the biological tissue. A processor 43 acquires a feature amount to be used for presuming at least either clinical condition or a physiological condition of the biological tissue of a subject according to change over time of the signal S1 due to the compression operation. An output interface 42 outputs a notification signal S3 corresponding to the feature amount.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to medical photometers used to estimate the physiological and / or pathological condition of living tissue of a subject. [Background technology]

[0002] Patent Document 1 discloses a pulse photometer, which is an example of a medical photometer. The pulse photometer is an apparatus that calculates the arterial blood oxygen saturation of a subject as an example of photometry. Specifically, light of a plurality of wavelengths having different ratios of the light absorption coefficients of blood is irradiated onto the living tissue of the subject. The amount of light of each wavelength that is transmitted through or reflected by the living tissue is subjected to detection. The amount of light of each wavelength changes with the pulsation of the blood of the subject. Therefore, the change over time in the amount of light of each wavelength caused by the pulsation is acquired as a pulse wave signal. The amplitude of the pulse wave signal for each wavelength corresponds to the amount of change in light attenuation for that wavelength. The arterial blood oxygen saturation is calculated based on the ratio of the amount of change in light attenuation for each wavelength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4196209 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to make it possible to estimate at least one of a pathological condition of a subject and a physiological state of living tissue by using the principle of photometry. [Means for solving the problem]

[0005] One aspect of the present invention to achieve the above object is a medical photometer, comprising: an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating at least one of a pathological condition of the subject and a physiological state of the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface for outputting a signal corresponding to the feature amount; It is equipped with:

[0006] According to such a configuration, the user can estimate at least one of the pathological condition of the subject and the physiological state of the biological tissue, based on a signal corresponding to a feature obtained using the principle of photometry.

[0007] One aspect of the present invention to achieve the above object is a medical photometer, comprising: an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor that acquires a feature amount from a time-dependent change in the signal accompanying the pressing operation, and estimates at least one of a pathological condition of the subject and a physiological state of the biological tissue based on the feature amount; an output interface for outputting a signal corresponding to a result of the estimation; It is equipped with:

[0008] According to this configuration, it is possible to cause the medical photometer to estimate at least one of the pathological condition of the subject and the physiological state of the living tissue, based on the feature amount obtained using the principle of photometry.

[0009] One aspect of the present invention to achieve the above object is a medical photometer, comprising: an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor that estimates at least one of a pathological condition of the subject and a physiological state of a biological tissue from a time-dependent change in the signal accompanying the compressing motion, using a classifier that has learned a relationship between a feature amount in the signal acquired from each of a plurality of subjects and at least one of a pathological condition and a physiological state of a biological tissue of each of the plurality of subjects as training data; an output interface for outputting a signal corresponding to a result of the estimation; It is equipped with:

[0010] This configuration allows the medical photometer to perform empirical estimation of the pathological condition of the subject and / or the physiological state of the tissue through machine learning using data previously acquired from multiple subjects, which increases the flexibility of the system compared to strict rule-based estimation. [Brief description of the drawings]

[0011] [Figure 1] 1 illustrates an example configuration of a medical photometry system according to an embodiment. [Diagram 2] 1 illustrates an example of the operation of a medical photometer according to an embodiment. [Diagram 3] 13 illustrates another example of the operation of a medical photometer according to an embodiment. [Figure 4] 13 illustrates another example of the operation of a medical photometer according to an embodiment. [Diagram 5] 13 illustrates another example of the operation of a medical photometer according to an embodiment. [Figure 6] 13 illustrates another example of the operation of a medical photometer according to an embodiment. [Figure 7] 13 illustrates another example of the operation of a medical photometer according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. In each drawing, the scale is appropriately changed so that each element to be described can be clearly seen.

[0013] 1 illustrates an example of a functional configuration of a medical photometry system 1 according to an embodiment. The medical photometry system 1 includes a light-emitting unit 10, a light-receiving unit 20, a compression device 30, and a medical photometer 40.

[0014] The light-emitting unit 10 can be attached to, for example, the fingertip of a subject. The light-emitting unit 10 includes at least one light source. The light source is a semiconductor light-emitting element configured to emit light containing a specific wavelength. Examples of the semiconductor light-emitting element include a light-emitting diode (LED), a laser diode, and an organic EL element.

[0015] The light receiving unit 20 can be attached to, for example, the fingertip of the subject. The light receiving unit 20 is disposed at a position where it can receive the light emitted from the light emitting unit 10 and transmitted through the biological tissue of the fingertip. In the illustrated example, the light emitting unit 10 and the light receiving unit 20 are disposed on opposite sides of the biological tissue of the fingertip. In this case, the light receiving unit 20 receives the light emitted from the light emitting unit 10 and transmitted through the biological tissue of the fingertip. The transmission of the biological tissue is an example of the passage of the biological tissue.

[0016] Alternatively, the light-emitting unit 10 and the light-receiving unit 20 may be disposed on the same side of the biological tissue of the fingertip. In this case, the light-receiving unit 20 receives light that is emitted from the light-emitting unit 10 and reflected by the biological tissue of the fingertip. Reflection by biological tissue is an example of light passing through biological tissue.

[0017] The light receiving unit 20 is an optical sensor having sensitivity to the wavelength of the light emitted from the light emitting unit 10. Examples of the optical sensor include a photodiode, a phototransistor, and a photoresistor. The light receiving unit 20 is configured to output a signal S1 according to the intensity of the light that has passed through the biological tissue.

[0018] The compression device 30 is attached to, for example, a fingertip of a subject. The compression device 30 is configured to be able to compress biological tissue of the fingertip through which light emitted from the light emitting unit 10 passes. The compression device 30 may include a cuff that compresses the biological tissue by air pressure, an actuator that compresses the biological tissue by a movable member, and the like.

[0019] The compression strength can be defined as a pressure sufficiently higher than the arterial blood pressure in the biological tissue. When a cuff is used, the air pressure can be, for example, 300 mmHg. When an actuator is used, the pressing force can be, for example, 500 gf. This can expel blood and interstitial fluid from the compressed biological tissue.

[0020] The medical photometer 40 includes an input interface 41, an output interface 42, a processor 43, a compression control unit 44, and a communication bus 45. The input interface 41, the output interface 42, the processor 43, and the compression control unit 44 are connected to each other via the communication bus 45 so as to be able to communicate with each other.

[0021] The processor 43 outputs a control signal S2 for controlling the operation of the light-emitting unit 10 from the output interface 42. The output interface 42 may include an appropriate signal conversion circuit as necessary. The signal conversion circuit converts the signal or data output from the processor 43 into a control signal S2 in a form capable of operating the light-emitting unit 10.

[0022] The input interface 41 receives the signal S1 output from the light receiving unit 20. The input interface 41 may include an appropriate signal conversion circuit as necessary. The signal conversion circuit converts the signal S1 into a signal or data in a form that allows the processor 43 to execute the process described below.

[0023] The compression control unit 44 is configured to change at least one of the thickness of the biological tissue, the amount of blood contained in the biological tissue, the amount of interstitial fluid contained in the biological tissue, the amount of blood flowing into the biological tissue, and the amount of blood flowing out of the biological tissue by controlling the compression operation by the compression device 30 attached to the subject's body.

[0024] When the compression device 30 includes a cuff, the compression control unit 44 may include a pump and a valve for adjusting the air pressure in the cuff. When the compression device 30 includes an actuator, the compression control unit 44 may include a circuit for outputting a control signal for adjusting the displacement amount of the actuator. In this case, the control signal may be output from the output interface 42. The operation of the compression control unit 44 may be controlled by the processor 43.

[0025] The processor 43 is configured to acquire a feature quantity used for estimating at least one of the physiological state of the biological tissue and the pathological condition of the subject from a time-dependent change in the signal S1 accompanying the pressing operation by the pressing device 30. The operation of the processor 43 will be described below with some specific examples.

[0026] Example 1: Estimation of pathological conditions in which oxygenation of the capillary bed is reduced In this example, the light emitting unit 10 includes a first light source that emits red light and a second light source that emits infrared light. The wavelengths of the red light and the infrared light are determined so that they are absorbed by hemoglobin in blood at different levels. An example of the wavelength of the red light is 660 nm. An example of the wavelength of the infrared light is 940 nm.

[0027] The processor 43 outputs a control signal S2 that causes the light-emitting unit 10 to alternately emit red light and infrared light from the output interface 42. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of the red light that has passed through the biological tissue and a signal S12 corresponding to the received light intensity of the infrared light that has passed through the biological tissue. The input interface 41 alternately receives the signal S11 and the signal S12.

[0028] The processor 43 acquires the change over time of the intensity of the signal S11 and the change over time of the intensity of the signal S12 while causing the compression control unit 44 to control the compression operation by the compression device 30. Fig. 2A illustrates an example of the change over time of the intensity of the signal S11 and the intensity of the signal S12 acquired in this manner.

[0029] Reference t1 indicates the time point when the compression operation by the compression device 30 is started. As the compression reduces the thickness of the biological tissue and expels blood, the received intensity of the red light and the received intensity of the infrared light at the light receiving unit 20 increases. Therefore, the intensity of the signal S11 and the signal S12 also increase.

[0030] Reference t2 indicates the time when the compression operation by the compression device 30 is released. As the compression is released, the thickness of the biological tissue recovers and the expelled blood returns, so that the received intensity of the red light and the received intensity of the infrared light at the light receiving unit 20 decrease. Therefore, the intensity of the signal S11 and the signal S12 also decrease.

[0031] Since the absorbance of red light by hemoglobin is different from the absorbance of infrared light, the intensity of the signal S11 is different from the intensity of the signal S12. The processor 43 acquires a difference value between the intensity of the signal S11 and the intensity of the signal S12. FIG. 2B illustrates an example of a change over time of the difference value acquired in this manner. The difference value corresponds to the difference between the received intensity of red light and the received intensity of infrared light at the light receiving unit 20. The acquisition of the difference value may be performed every time the signal S11 and the signal S12 are received, or may be performed after the acquisition of the signal S11 and the signal S12 for a specific period is completed. The difference value between the intensity of the signal S11 and the intensity of the signal S12 is an example of a first correlation value between the intensity of the signal S11 and the intensity of the signal S12.

[0032] The processor 43 acquires a difference value D21 (=d2-d1) between the difference value d1 at time t1 and the difference value d2 at time t2 as a feature. The difference value d1 is an example of a first correlation value before the compression operation by the compression device 30 is performed. The difference value d2 is an example of a first correlation value after the compression operation by the compression device 30 is performed. The difference value D21 is an example of a second correlation value.

[0033] As another example of the first correlation value, the ratio between the intensity of the signal S11 and the intensity of the signal S12 may be obtained. In this case, as another example of the second correlation value, the difference between the ratio at time t1 and the ratio at time t2 is obtained.

[0034] The difference value D21 reflects the oxygenation state of the blood removed from the biological tissue by compression. For example, in a patient with sepsis, a shunt blood flow occurs in which blood flows from an artery to a vein without passing through a capillary bed. When a shunt blood flow occurs, the amount of blood and oxygen supplied to the biological tissue including the capillary bed decreases, and the blood oxygen saturation of the capillary bed decreases. In this case, the intensity of the signal S12 increases, and the difference value D21 decreases. When the decrease in blood oxygen saturation is significant, the difference value D21 may be a negative value.

[0035] The processor 43 outputs a notification signal S3 corresponding to the difference value D21 from the output interface 42. As illustrated in FIG. 1, the medical photometer 40 may include a notification unit 49. The notification unit 49 may perform notification based on the notification signal S3. The notification is performed using at least one of visual notification, audio notification, and tactile notification. For example, an indicator indicating the difference value D21 may be displayed on a display device. Alternatively, when the difference value D21 falls below a predetermined threshold, an appropriate indicator may be displayed or an alarm sound may be output. The notification based on the notification signal S3 may be performed by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0036] According to this configuration, the user can infer that the subject is suffering from a pathological condition in which the oxygenation state of the capillary bed is reduced through the notification based on the difference value D21. As described above, one example of such a pathological condition is sepsis.

[0037] Instead of outputting the notification signal S3 corresponding to the difference value D21, the processor 43 may output a notification signal S4 corresponding to an inferred result of a pathological condition in which the oxygenation state of the capillary bed is reduced. In this case, the processor 43 is configured to infer that the subject has a pathological condition in which the oxygenation state of the capillary bed is reduced when the difference value D21 falls below a predetermined threshold.

[0038] The notification unit 49 may issue a notification based on the notification signal S4. The notification may be made using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that sepsis is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0039] Example 2: Estimation of intraperitoneal bleeding In this example, the light emitting unit 10 includes a first light source that emits a first infrared light and a second light source that emits a second infrared light. The wavelength of the first infrared light is determined so that the difference between the absorbance by oxygenated hemoglobin and the absorbance by deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is less affected by changes in oxygenation state is selected. An example of such a wavelength of the first infrared light is 805 nm. The wavelength of the second infrared light is determined so that the absorbance by water is greater than that by hemoglobin. An example of such a wavelength of the second infrared light is 1300 nm.

[0040] The processor 43 outputs a control signal S2 from the output interface 42 to cause the light-emitting unit 10 to alternately emit the first infrared light and the second infrared light. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of the first infrared light that has passed through the biological tissue and a signal S12 corresponding to the received light intensity of the second infrared light that has passed through the biological tissue. The input interface 41 alternately receives the signals S11 and S12. The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12 while causing the compression control unit 44 to control the compression operation by the compression device 30.

[0041] In the same manner as in Example 1, the processor 43 obtains a difference value between the intensity of the signal S11 and the intensity of the signal S12. As a result, the change over time of the difference value becomes as illustrated in FIG. 2B. The difference value between the intensity of the signal S11 and the intensity of the signal S12 is an example of a correlation value. Another example of the correlation value is the ratio of the intensity of the signal S11 to the intensity of the signal S12.

[0042] The processor 43 acquires a difference value D21 (=d2-d1) between the difference value d1 at time t1 and the difference value d2 at time t2 as a feature. The difference value d1 is an example of a first correlation value before the compression operation by the compression device 30 is performed. The difference value d2 is an example of a first correlation value after the compression operation by the compression device 30 is performed. The difference value D21 is an example of a second correlation value.

[0043] As another example of the first correlation value, the ratio between the intensity of the signal S11 and the intensity of the signal S12 may be obtained. In this case, as another example of the second correlation value, the difference between the ratio at time t1 and the ratio at time t2 is obtained.

[0044] The difference value D21 reflects the anemia state of the subject. For example, in a patient suffering from intraperitoneal bleeding, a decrease in hemoglobin concentration (anemia) appears as a clinical symptom. In this case, the intensity of the signal S11 increases, so the difference value D21 decreases. When the anemia symptom is severe, the difference value D21 may take a negative value.

[0045] The processor 43 outputs a notification signal S3 corresponding to the difference value D21 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification is provided using at least one of a visual notification, an auditory notification, and a tactile notification. For example, an indicator indicating the difference value D21 can be displayed on a display device. Alternatively, when the difference value D21 falls below a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0046] According to this configuration, the user can estimate intraperitoneal bleeding of the subject through the notification based on the difference value D21. Intraperitoneal bleeding is an example of a pathological condition.

[0047] Instead of outputting the notification signal S3 corresponding to the difference value D21, the processor 43 may output a notification signal S4 corresponding to an estimated result of intraperitoneal bleeding. In this case, the processor 43 is configured to estimate intraperitoneal bleeding of the subject when the difference value D21 falls below a predetermined threshold.

[0048] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an audible notification, and a tactile notification. For example, a suitable indicator indicating that intraperitoneal bleeding is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0049] Example 3: Estimation of pathological conditions that cause decreased oxygenation of the capillary bed In this example, the light-emitting unit 10 includes a light source that emits red light. The wavelength of the red light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is greater than a predetermined value. In other words, a wavelength whose absorbance is easily affected by changes in the oxygenation state is selected. An example of such a wavelength of red light is 660 nm.

[0050] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit red light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the red light that has passed through the biological tissue. The input interface 41 receives the signal S1.

[0051] The processor 43 acquires the change over time of the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. Fig. 3 illustrates an example of the change over time of the intensity of the signal S1 acquired in this manner.

[0052] Reference t1 indicates the time point when the compression operation by the compression device 30 is started. As the compression reduces the thickness of the biological tissue and expels blood, the intensity of the red light received by the light receiving unit 20 increases. Therefore, the intensity of the signal S1 also increases.

[0053] Reference t2 indicates the time when the compression by the compression device 30 is released. As the compression is released, the thickness of the biological tissue is restored and the expelled blood returns, so that the intensity of the red light received by the light receiving unit 20 decreases. Therefore, the intensity of the signal S1 also decreases.

[0054] Reference t3 represents the time point at which the amount of change in the intensity of the signal S1 per unit time after the compression is released reaches a predetermined threshold value.

[0055] At time t4 after time t3, the intensity of the signal S1 reaches a steady state where it does not change substantially over time. Symbol i4 represents the intensity of the signal S1 in the steady state. The processor 43 acquires, as a feature, a difference value I31 (=i3-i1) between the intensity i1 of the signal S1 at time t1 and the intensity i3 of the signal S1 at time t3. The intensity i1 is an example of the intensity before the compression operation by the compression device 30 is performed. The intensity i3 is an example of the intensity after the compression operation by the compression device 30 is released. The difference value I31 is an example of a correlation value. Another example of the correlation value is the ratio of the intensity i1 to the intensity i3.

[0056] The difference value I31 reflects the oxygenation state of the blood removed from the living tissue by compression. For example, in a patient with sepsis, a shunt blood flow occurs in which blood flows from an artery to a vein without passing through a capillary bed. When a shunt blood flow occurs, the amount of blood and oxygen supplied to the living tissue including the capillary bed decreases, so the blood oxygen saturation of the capillary bed decreases. In this case, the absorption of red light increases, so the intensity i1 decreases. On the other hand, after the compression operation is released, arterial blood with high oxygen saturation flows into the capillary bed, so the oxygen saturation of the capillary bed immediately after the compression is released is higher than that of the capillary bed before the compression. At this time, the absorption of red light decreases, so the intensity i3 at time t3 increases, and the difference value I31 increases.

[0057] The processor 43 outputs a notification signal S3 corresponding to the difference value I31 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of visual notification, auditory notification, and tactile notification. For example, an indicator indicating the difference value I31 can be displayed on a display device. Alternatively, when the difference value I31 falls below a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0058] According to this configuration, the user can infer that the subject is suffering from a pathological condition in which the oxygenation state of the capillary bed is reduced through the notification based on the difference value I31. As described above, one example of such a pathological condition is sepsis.

[0059] Instead of outputting the notification signal S3 corresponding to the difference value I31, the processor 43 may output a notification signal S4 corresponding to an inferred result of a pathological condition in which the oxygenation state of the capillary bed is reduced. In this case, the processor 43 is configured to infer that the subject has a pathological condition in which the oxygenation state of the capillary bed is reduced when the difference value I31 falls below a predetermined threshold.

[0060] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that sepsis is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0061] As illustrated in Fig. 3, time t5 may be defined as necessary. Time t5 is the time when the intensity of signal S1 recovers to a predetermined ratio with respect to the difference value I23 (=i2-i3) between intensity i2 and intensity i3. That is, intensity i5 at time t5 is specified as a value obtained by multiplying difference value I23 by a predetermined ratio and adding the result to intensity i3. The predetermined ratio is, for example, 0.1. In this case, a difference value I51 (=i5-i1) between intensity i5 and intensity i1, or the like, may be defined as a new feature amount as necessary.

[0062] Example 4: Estimation of edema In this example, the light emitting unit 10 includes a light source that emits infrared light. The wavelength of the infrared light is determined so that it is more absorbed by water than by hemoglobin. An example of the wavelength of the infrared light is 1300 nm.

[0063] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit near-infrared light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the red light that has passed through the biological tissue. The input interface 41 receives the signal S1.

[0064] The processor 43 acquires the change over time in the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. As the thickness of the biological tissue decreases and the interstitial fluid is eliminated with compression, the intensity of the infrared light received by the light receiving unit 20 increases. Therefore, the intensity of the signal S1 also increases. When the thickness of the biological tissue is restored with the release of compression, the eliminated interstitial fluid returns, and the intensity of the near-infrared light received by the light receiving unit 20 decreases. Therefore, the intensity of the signal S1 also decreases. As a result, the change over time in the intensity of the signal S1 becomes as shown in FIG. 3.

[0065] The processor 43 acquires a difference value I31 (=i3-i1) between the intensity i1 of the signal S1 at time t1 and the intensity i3 of the signal S1 at time t3 as a feature. The intensity i1 is an example of the intensity before the compression operation by the compression device 30 is performed. The intensity i3 is an example of the intensity after the compression operation by the compression device 30 is released. The difference value I31 is an example of a correlation value. Another example of the correlation value is the ratio of the intensity i1 to the intensity i3.

[0066] The difference value I31 can be used to estimate edema. In patients with edema, excess water is stored in the interstitium. It takes time for the water removed by the compression to be refilled in the interstitium. Therefore, the reduced thickness of the biological tissue continues even after the compression is released. In this case, the intensity i3 increases, and the difference value I31 becomes large. When the degree of edema is significant, i.e., when a significantly large amount of water is removed by the compression,

[0067] The processor 43 outputs a notification signal S3 corresponding to the difference value I31 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of visual notification, auditory notification, and tactile notification. For example, an indicator indicating the difference value I31 can be displayed on a display device. Alternatively, when the difference value I31 falls below a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0068] According to this configuration, the user can infer that the subject has edema through the notification based on the difference value I31. Edema is an example of a pathological condition.

[0069] Instead of outputting the notification signal S3 corresponding to the difference value I31, the processor 43 may output a notification signal S4 corresponding to an estimated result of edema. In this case, the processor 43 is configured to estimate that the subject has edema when the difference value I31 falls below a predetermined threshold.

[0070] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that edema is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0071] The processor 43 may acquire, in addition to or instead of the difference value I31, an area Au under the waveform in the change over time of the intensity of the signal S1 after the time t2 at which the compression operation is released, as a feature amount. Specifically, the area Au under the waveform is expressed by the following formula 1 for the change over time i(t) of the intensity of the signal S1.

number

[0072] For example, as blood flow increases, the signal intensity i3 may fall below the signal intensity i4. In this case, the area under the waveform Au is expressed by the following equation 2.

number

[0073] The area under the waveform Au can also be used to estimate edema. In patients with edema, there is excess fluid stored in the interstitial space. The fluid removed by the compression motion takes time to be refilled in the interstitial space. Therefore, the area under the waveform Au becomes large. If the area under the waveform Au exceeds a certain threshold, it can be estimated that the subject has edema.

[0074] Example 5: Estimation of vascular status and vascular reactivity In this example, the light-emitting unit 10 includes a light source that emits infrared light. The wavelength of the infrared light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is not easily affected by changes in oxygenation state is selected. Examples of such wavelengths of red light include 805 nm and 940 nm.

[0075] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit infrared light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the infrared light that has passed through biological tissue. The input interface 41 receives the signal S1.

[0076] The processor 43 acquires the change over time of the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. As a result, the change over time of the intensity of the signal S1 acquired in this manner is as shown in FIG.

[0077] The processor 43 acquires, as a feature, a difference value I31 (=i3-i1) between the intensity i1 of the signal S1 at time t1 and the intensity i3 of the signal S1 at time t3. The intensity i1 is an example of the intensity before the compression operation by the compression device 30 is performed. The intensity i3 is an example of the intensity after the compression operation by the compression device 30 is released. The difference value I13 is an example of a correlation value. Another example of the correlation value is the ratio of the intensity i1 to the intensity i3.

[0078] When blood flow is temporarily stopped and then resumed, the blood vessels expand due to the reaction of the vascular endothelium, and the blood flow increases more than before the blood flow was stopped. This phenomenon is known as reactive hyperemia. A flow-mediated dilation (FMD) test is known as a diagnostic method for vascular endothelial function that utilizes this physiological stimuli responsiveness. In this test, if the increase in blood vessel diameter is smaller than the normal range, it suggests a pathological condition in which vascular endothelial function is reduced. The above phenomenon can be induced by the compression operation by the compression device 30 and its release. If the blood flow increases compared to before compression due to the release of compression, the intensity i3 decreases, and the difference value I31 becomes smaller. If the increase in blood flow is significant, the difference value I31 can be a negative value. In FIG. 3, the signal intensity when the difference value I31 is a negative value is exemplified by the symbol i3'.

[0079] The processor 43 outputs a notification signal S3 corresponding to the difference value I31 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 is provided using at least one of a visual notification, an auditory notification, and a tactile notification. For example, an indicator indicating the difference value I31 can be displayed on a display device. Alternatively, when the difference value I31 falls below a predetermined threshold, an appropriate indicator indicating a decrease in vascular endothelial function can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device through the output interface 42.

[0080] According to this configuration, the user can estimate the vascular endothelial function of the subject through the notification based on the difference value I31. The vascular endothelial function is an example of a physiological state of biological tissue.

[0081] Instead of outputting the notification signal S3 corresponding to the difference value I31, the processor 43 may output a notification signal S4 corresponding to an inferred result of a pathological condition in which vascular endothelial function is impaired. In this case, the processor 43 is configured to infer that the subject is in a pathological condition in which vascular endothelial function is impaired when the difference value I31 falls below a predetermined threshold.

[0082] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that a decrease in vascular endothelial function is estimated may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0083] As in Example 4, the processor 43 may acquire, in addition to or instead of the difference value I31, the area Au under the waveform in the change over time in the intensity of the signal S1 after the time t2 at which the compressing motion is released, as a feature amount.

[0084] The area under the waveform Au can also be used to estimate the vascular condition and vascular reactivity. As described above, when the blood flow increases due to the reactive hyperemia after the compression motion is released, the intensity i3 decreases. Therefore, the area under the waveform increases, as illustrated in FIG. 3. If the area under the waveform exceeds a predetermined threshold, it can be estimated that the subject is in a pathological condition in which vascular endothelial function is impaired.

[0085] As shown in Fig. 4(A), a waveform corresponding to the subject's pulse wave is superimposed on the signal S1. Fig. 4(B) shows an enlarged example of the waveform. In the following description, the waveform will be referred to as a "pulse wave" for convenience. As shown in Fig. 4(B), multiple waveform factors can be defined for the pulse wave. Ap: Amplitude (difference between maximum and minimum signal strength) Tf: Fall time (the time from when the signal strength reaches its maximum value to when it reaches its minimum value) Gf: Falling slope (=A / Tf) Tr: Rise time (the time from when the signal strength reaches its minimum value to when it reaches its maximum value) Gr: Falling slope (=A / Tr)

[0086] As a value corresponding to the amplitude A, a statistical quantity such as the root mean square error (RMSE), Euclidean distance, mean square error (MSE), or standard deviation (SD) of the intensity values ​​of the signal S1 in a predetermined period of time can be used.

[0087] In addition to or instead of the difference value I31, the processor 43 may acquire, as a feature amount, a correlation value between a waveform factor of a pulse wave superimposed on the signal S1 before a compression operation and a waveform factor of a pulse wave superimposed on the signal S1 after the compression operation has been performed. Examples of the correlation value include a difference value or a ratio.

[0088] In the area surrounded by the dashed line C1 in Fig. 4A, a pulse wave is superimposed on the signal S1 before the compression operation. The above-mentioned waveform factors of the pulse wave are represented as amplitude Ap1, fall time Tf1, fall gradient Gf1, rise time Tr1, and rise gradient Gr1. In the area surrounded by the dashed line C2 in Fig. 4A, a pulse wave is superimposed on the signal S1 after the compression operation. The above-mentioned waveform factors of the pulse wave are represented as amplitude Ap2, fall time Tf2, fall gradient Gf2, rise time Tr2, and rise gradient Gr2.

[0089] The processor 43 obtains correlation values ​​for waveform factors of the same type. For example, when focusing on the amplitude Ap, the processor 43 obtains a difference value (Ap1-Ap2) or a ratio (Ap1 / Ap2) as a feature. Similarly, a difference value (Tf1-Tf2) or a ratio (Tf1 / Tf2), a difference value (Gf1-Gf2) or a ratio (Gf1 / Gf2), a difference value (Tr1-Tr2) or a ratio (Tr1 / Tr2), and a difference value (Gr1-Gr2) or a ratio (Gr1 / Gr2) can be obtained.

[0090] It is known that the shape of the pulse wave changes according to blood pressure, blood flow, vascular resistance, etc., as expressed by the Windkessel model. Therefore, the feature quantity based on the waveform factor of the pulse wave reflects the subject's vascular condition and vascular reactivity to physiological stimuli. Other examples of such waveform factors include percentile, kurtosis, skewness, etc. Therefore, through notification based on the correlation value, the user can estimate the subject's vascular condition and vascular reactivity to physiological stimuli. The vascular condition and vascular reactivity to physiological stimuli are examples of the physiological condition of biological tissue.

[0091] Example 6: Predicting signs of shock when blood pressure drops In this example, the light-emitting unit 10 includes a light source that emits infrared light. The wavelength of the infrared light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is not easily affected by changes in oxygenation state is selected. Examples of such wavelengths of red light include 805 nm and 940 nm.

[0092] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit infrared light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the infrared light that has passed through biological tissue. The input interface 41 receives the signal S1.

[0093] The processor 43 acquires the change over time of the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. As a result, the change over time of the intensity of the signal S1 acquired in this manner is as shown in Fig. 5. For this change over time, the following five periods and five gradients can be defined.

[0094] When the compression operation starts at time t1, the intensity of the signal S1 increases rapidly. Therefore, the derivative of the intensity of the signal S1 also increases rapidly. Thereafter, the increase in the intensity of the signal S1 gradually becomes more gradual. Therefore, the derivative of the intensity of the signal S1 starts to decrease. A period from time t1 when the compression operation starts to a time when the derivative falls below a predetermined threshold value Th1 is defined as a first period T1. The amount of change in the intensity of the signal S1 during the first period T1 is defined as a first gradient G1. The first period T1 is an example of a predetermined time.

[0095] The period from the end of the first period T1 to the time t2 when the compression operation is released is defined as a second period T2. The amount of change in the intensity of the signal S1 during the second period T2 is defined as a second gradient G2. The second period T2 is an example of a predetermined time.

[0096] In other words, the first period T1 is a period during which the amount of change in the intensity of the signal S1 during the compressing motion is relatively large, and the second period T2 is a period during which the amount of change in the intensity of the signal S1 during the compressing motion is relatively small.

[0097] When the compression operation is released, the intensity of the signal S1 decreases rapidly. Therefore, the derivative of the intensity of the signal S1 also decreases rapidly. After that, the decrease in the intensity of the signal S1 becomes gradually more gradual. Therefore, the derivative of the intensity of the signal S1 starts to increase. The period from the time t2 when the compression operation is released to the time when the derivative exceeds a predetermined threshold value Th3 is defined as a third period T3. The amount of change in the intensity of the signal S1 during the third period T3 is defined as a third gradient G3. The third period T3 is an example of a predetermined time.

[0098] The period from the end of the third period T3 to time t3 is defined as a fourth period T4. As described above, time t3 is the time when the change in the intensity of the signal S1 per predetermined time period after the compression motion is released reaches a predetermined threshold. The change in the intensity of the signal S1 during the fourth period T4 is defined as a fourth gradient G4. The fourth period T4 is an example of a predetermined time.

[0099] In other words, the third period T3 is a period in which the amount of change in the intensity of the signal S1 after the compression is released is relatively large, and the fourth period T4 is a period in which the amount of change in the intensity of the signal S1 after the compression is released is relatively small.

[0100] The period from time t3 to time t4 is defined as a fifth period T5. The amount of change in the intensity of the signal S1 during the fifth period T5 is defined as a fifth gradient G5. The fifth period T5 is an example of a predetermined time.

[0101] Each of the first gradient G1, the second gradient G2, the third gradient G3, the fourth gradient G4, and the fifth gradient G5 is obtained by fitting a linear function using the least squares method or the like. However, the function to be fitted may be an exponential function or a power function. When fitting an exponential function, the feature value obtained is a time constant. When fitting a power function, the feature value obtained is a coefficient of each term.

[0102] The processor 43 acquires the fourth gradient G4 as the feature amount. The fourth gradient G4 is an example of the amount of change in the intensity of infrared light per predetermined time after the compression motion is released.

[0103] The fourth gradient G4 can be used to estimate a sign of shock, which is a drop in blood pressure. Before a sudden drop in blood pressure occurs, the body performs autonomous hemodynamic regulation to maintain blood pressure by constricting peripheral blood vessels and increasing peripheral vascular resistance. If this autonomous regulation function cannot be maintained, blood pressure drops suddenly and the body falls into a state of shock. When the peripheral blood vessels constrict, the return of blood slows down after the compression action is released, so the recovery of the intensity of the signal S1 also slows down, and the value of the fourth gradient G4 increases (the negative gradient becomes gentler).

[0104] The processor 43 outputs a notification signal S3 corresponding to the fourth gradient G4 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of a visual notification, an auditory notification, and a tactile notification. For example, an indicator indicating the fourth gradient G4 can be displayed on a display device. Alternatively, when the fourth gradient G4 exceeds a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0105] According to this configuration, the user can estimate the symptom of shock, which is manifested by a drop in blood pressure of the subject, through the notification based on the fourth gradient G4. The symptom of shock, which is manifested by a drop in blood pressure, is an example of a pathological condition.

[0106] Instead of outputting the notification signal S3 corresponding to the fourth gradient G4, the processor 43 may output a notification signal S4 corresponding to an estimated result of a sign of shock presenting a drop in blood pressure. In this case, the processor 43 is configured to estimate a sign of shock presenting a drop in the subject's blood pressure when the fourth gradient G4 falls below a predetermined threshold.

[0107] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator may be displayed to indicate that a symptom of shock, which is a drop in blood pressure, or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0108] Example 7: Estimation of oxygen metabolism in biological tissues In this example, the light emitting unit 10 includes a first light source that emits red light and a second light source that emits infrared light. The wavelengths of the red light and the infrared light are determined so that they are absorbed by hemoglobin in blood at different levels. An example of the wavelength of the red light is 660 nm. An example of the wavelength of the infrared light is 940 nm.

[0109] The processor 43 outputs a control signal S2 from the output interface 42, which causes the light-emitting unit 10 to alternately emit red light and infrared light. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of red light that has passed through biological tissue and a signal S12 corresponding to the received light intensity of infrared light that has passed through biological tissue. The input interface 41 alternately receives the signals S11 and S12. The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12, while causing the compression control unit 44 to control the compression operation by the compression device 30.

[0110] In the same manner as in Example 1, the processor 43 obtains a difference value between the intensity of the signal S11 and the intensity of the signal S12. As a result, the change over time of the difference value becomes as shown in FIG. 2B. After the compression operation is released, the difference value reaches a steady state in which the change over time of the difference value is substantially eliminated. The symbol d4 represents the difference value in the steady state. The difference value between the intensity of the signal S11 and the intensity of the signal S12 is an example of a correlation value. Another example of the correlation value is the ratio of the intensity of the signal S11 to the intensity of the signal S12.

[0111] In the figure, the reference character t3 indicates the time when the change in the intensity of the signal S1 per unit time after the compression is released reaches a predetermined threshold, and the reference character t4 indicates the time when the change in the intensity of the signal S1 over time reaches a steady state.

[0112] The processor 43 acquires a fifth gradient G5 of the change over time of the difference value as the feature amount. The definition of the fifth gradient G5 is the same as that of the fifth gradient G5 described with reference to FIG. 5. That is, the fifth gradient G5 is defined as the amount of change in the difference value occurring between time t3 and time t4. The fifth gradient G5 is an example of the amount of change in the difference value per predetermined time after the compression operation is released.

[0113] The fifth gradient G5 can be used to estimate the oxygen metabolism state in the biological tissue of the subject. The state in which the time-dependent change in the difference value shown in FIG. 2B reaches a steady state corresponds to a state in which the supply and consumption of oxygen are balanced. That is, biological tissue in which the supply and consumption of oxygen are balanced takes a short time to reach a steady state, so the value of the fifth gradient G5 is small (the negative gradient is steep). For example, in the biological tissue of a normal subject, oxygen in the blood flowing into the biological tissue after the compression operation is released is actively consumed, lowering the blood oxygen saturation. On the other hand, blood with high oxygen saturation smoothly flows into the biological tissue, raising the blood oxygen saturation. The balance between the two is established early, so the value of the fifth gradient G5 is small.

[0114] The processor 43 outputs a notification signal S3 corresponding to the fifth gradient G5 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 is provided using at least one of visual notification, auditory notification, and tactile notification. For example, an indicator indicating the fifth gradient G5 can be displayed on a display device. Alternatively, when the fifth gradient G5 exceeds a predetermined threshold (the negative gradient is gentle), an appropriate indicator indicating that the oxygen metabolism state is not good (oxygen supply and oxygen consumption are not balanced) can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0115] According to this configuration, the user can estimate the oxygen metabolic state in the capillary bed of the subject through the notification based on the fifth gradient G5. The oxygen metabolic state of the capillary bed is an example of a physiological state of biological tissue.

[0116] Instead of outputting the notification signal S3 corresponding to the fifth gradient G5, the processor 43 may output a notification signal S4 corresponding to an estimation result of the oxygen metabolic state of the capillary bed. In this case, the processor 43 is configured to estimate that the oxygen metabolic state in the capillary bed of the subject is not good when the fifth gradient G5 exceeds a predetermined threshold (has a gentle negative gradient).

[0117] The notification unit 49 can provide notification based on the notification signal S4. The notification based on the notification signal S4 is provided using at least one of a visual notification, an auditory notification, and a tactile notification. The notification based on the notification signal S4 may be provided by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0118] In this example, the light-emitting unit 10 can be configured to include a light source that emits only red light. In this case, the wavelength of the red light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is greater than a predetermined value. In other words, a wavelength whose absorbance is easily affected by changes in oxygenation state is selected. An example of such a wavelength of red light is 660 nm.

[0119] An example of an unsatisfactory oxygen metabolism state is one symptom in the progression process of sepsis. When a patient develops sepsis, a symptom called warm shock appears first, followed by a symptom called cold shock, and then a symptom called anaerobic metabolism. In a warm shock state, the arteries expand and peripheral vascular resistance decreases, increasing cardiac output and warming the limbs. In a cold shock state, the limbs feel cold and blood pressure drops, causing circulatory insufficiency, a state called cold shock. In this state, the peripheral vascular expansion ability decreases and cardiac output decreases. Under normal conditions, living tissues maintain their vital activity through aerobic metabolism, in which mitochondria consume oxygen to generate energy and carbon dioxide. However, when oxygen is not sufficiently supplied to tissues due to peripheral circulatory insufficiency, anaerobic metabolism is temporarily performed to generate energy without consuming oxygen in order to maintain vital activity.

[0120] In addition to the fifth gradient G5, the fourth gradient G4 in FIG. 2B is acquired as a feature, so that the aerobic metabolic state and the anaerobic metabolic state of the sepsis patient can be estimated. The definition of the fourth gradient G4 is the same as that of the fourth gradient G4 described with reference to FIG. 5. That is, the fourth gradient G4 is defined as the amount of change in the difference value occurring between time t2 and time t3. The fourth gradient G4 is an example of the amount of change in the difference value per predetermined time after the compression operation is released.

[0121] In the case of a patient with sepsis, the peripheral blood vessels are constricted and the return of blood is slowed down after the compression action is released, so the recovery of the strength of the difference value is also slowed down and the value of the fourth gradient G4 increases (the negative gradient becomes gentler).

[0122] In a cold shock state, the supply of oxygen is relatively low due to a lack of blood flow, while the consumption of oxygen is relatively high due to aerobic metabolism. Therefore, it takes time for the equilibrium between the supply and consumption of oxygen to be established after the compression operation is released. In other words, the value of the fifth gradient G5 increases (the negative gradient becomes gentler). On the other hand, in an anaerobic metabolism state, the supply of oxygen is relatively low due to a lack of blood flow, but the consumption of oxygen is also relatively low, so the equilibrium between the supply and consumption of oxygen after the compression operation is released is relatively fast. In other words, the value of the fifth gradient G5 decreases (the negative gradient becomes steeper).

[0123] Therefore, if the value of the fourth gradient G4 is smaller than a predetermined threshold and the value of the fifth gradient G5 is also smaller than a predetermined threshold, it can be estimated that the subject is normal and the oxygen metabolism state of the capillary bed is good. If the value of the fourth gradient G4 is equal to or greater than a predetermined threshold and the value of the fifth gradient G5 is smaller than a predetermined threshold, it can be estimated that the subject has sepsis and the capillary bed is in an anaerobic metabolic state. If the value of the fourth gradient G4 is equal to or greater than a predetermined threshold and the value of the fifth gradient G5 is also equal to or greater than a predetermined threshold, it can be estimated that the subject has sepsis and the capillary bed is in an aerobic metabolic state (i.e., a cold shock state).

[0124] In this case, the notification signal S3 may be configured to correspond to the fourth gradient G4 and the fifth gradient G5. The notification signal S4 may be configured to correspond to the estimation result related to the aerobic metabolic state and the anaerobic metabolic state in sepsis. The aerobic metabolic state and the anaerobic metabolic state in sepsis are examples of pathological conditions.

[0125] Example 8: Estimation of edema In this example, the light emitting unit 10 includes a first light source that emits a first infrared light and a second light source that emits a second infrared light. The wavelength of the first infrared light is determined so that the difference between the absorbance by oxygenated hemoglobin and the absorbance by deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is less affected by changes in oxygenation state is selected. An example of such a wavelength of infrared light is 805 nm. The wavelength of the second infrared light is determined so that the absorbance by water is greater than that by hemoglobin. An example of such a wavelength of the second infrared light is 1300 nm.

[0126] The processor 43 outputs a control signal S2 from the output interface 42 to cause the light-emitting unit 10 to alternately emit the first infrared light and the second infrared light. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of the first infrared light that has passed through the biological tissue and a signal S12 corresponding to the received light intensity of the second infrared light that has passed through the biological tissue. The input interface 41 alternately receives the signals S11 and S12. The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12 while causing the compression control unit 44 to control the compression operation by the compression device 30.

[0127] The processor 43 acquires data corresponding to a locus (change over time) of points determined by the intensities of the signals S11 and S12 in a coordinate plane formed by a first coordinate axis corresponding to the intensity of the signal S11 and a second coordinate axis corresponding to the intensity of the signal S12, as illustrated in Fig. 6. As shape factors of the locus, a first gradient Φ1, a second gradient Φ2, a third gradient Φ3, a fourth gradient Φ4, a fifth gradient Φ5, a first area A1, a second area A2, and a total area A0 can be defined.

[0128] The first gradient Φ1 is defined as the gradient of the trajectory drawn on the coordinate plane of FIG. 6 during the first period T1 described with reference to FIG. 5. The second gradient Φ2 is defined as the gradient of the trajectory drawn on the coordinate plane of FIG. 6 during the second period T2 described with reference to FIG. 5. The third gradient Φ3 is defined as the gradient of the trajectory drawn on the coordinate plane of FIG. 6 during the third period T3 described with reference to FIG. 5. The fourth gradient Φ4 is defined as the gradient of the trajectory drawn on the coordinate plane of FIG. 6 during the fourth period T4 described with reference to FIG. 5. The fifth gradient Φ5 is defined as the gradient of the trajectory drawn on the coordinate plane of FIG. 6 during the fifth period T5 described with reference to FIG. 5.

[0129] Each of the first gradient G1, the second gradient G2, the third gradient G3, the fourth gradient G4, and the fifth gradient G5 is obtained by fitting a linear function using the least squares method or the like. However, the function to be fitted may be an exponential function or a power function. When fitting an exponential function, the feature value obtained is a time constant. When fitting a power function, the feature value obtained is a coefficient of each term.

[0130] In the coordinate plane, when a line connecting a point determined by the intensities of the signals S11 and S12 at time t1 and a point determined by the intensities of the signals S11 and S12 at time t2 is represented by L1, the first area A1 represents an area enclosed by the line L1 and a locus drawn by points determined by the intensities of the signals S11 and S12 from time t1 to time t2. In other words, it represents an area enclosed by the line L1 and a locus drawn by points determined by the intensities of the signals S11 and S12 before the compression motion is released.

[0131] Similarly, when a line connecting a point determined by the intensities of the signals S11 and S12 at time t2 and a point determined by the intensities of the signals S11 and S12 at time t4 is represented by L2, the second area A2 represents an area surrounded by the line L2 and a locus drawn by the points determined by the intensities of the signals S11 and S12 from time t2 to time t4. In other words, it represents an area surrounded by the line L2 and a locus drawn by the points determined by the intensities of the signals S11 and S12 after the compression motion is released. The total area A0 is defined as the sum of the first area A1 and the second area A2.

[0132] The processor 43 acquires at least one of these shape factors as a feature amount. The feature amount is used, for example, to estimate edema.

[0133] In patients with edema, excess water is stored in the interstitium. It takes time for the water removed by the compression to be refilled in the interstitium. That is, when the compression is released, the blood removed by the compression returns to the tissue first, and the intensity of the signal S11 reflecting the amount of light absorbed by hemoglobin recovers first. Then, the water gradually returns to the interstitium, and the intensity of the signal S12 reflecting the amount of light absorbed by water recovers. Therefore, there are significant differences between subjects without edema, especially in the third gradient Φ3, fourth gradient Φ4, fifth gradient Φ5, second area A2, and total area A0 reflecting the change in the intensity of the signal S11 and the change in the intensity of the signal S12 immediately before and after the compression is released. Therefore, the ratio (A2 / A1) of the second area A2 to the first area A1 and the ratio (A2 / A0) of the second area A2 to the total area A0 can also be shape factors.

[0134] The processor 43 outputs a notification signal S3 corresponding to at least one shape factor from the output interface 42. The notification unit 49 may issue a notification based on the notification signal S3. The notification based on the notification signal S3 is issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, an indicator indicating the second area A2 may be displayed on a display device. For example, when the second area A2 exceeds a predetermined threshold, an appropriate indicator may be displayed or an alarm sound may be output. The notification based on the notification signal S3 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0135] In addition to or instead of the notification signal S3 corresponding to at least one shape factor, the processor 43 may output a signal for displaying an image including a coordinate plane and a locus of points determined by the intensities of the signals S11 and S12, as exemplified in Fig. 6, from the output interface 42. Based on the signal, the image can be displayed on a display device (not shown) provided in the medical photometer 40 or on a display device remote from the medical photometer 40.

[0136] According to this configuration, the user can infer that the subject has edema through the notification based on at least one shape factor. Edema is an example of a pathological condition.

[0137] Instead of outputting the notification signal S3 corresponding to at least one shape factor, the processor 43 may output a notification signal S4 corresponding to an estimated result of edema. For example, the processor 43 is configured to estimate that the subject has edema when the second area A2 exceeds a predetermined threshold.

[0138] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that edema is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0139] Example 9: Estimation of septic shock symptoms In this example, the light-emitting unit 10 includes a light source that emits infrared light. The wavelength of the infrared light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is not easily affected by changes in oxygenation state is selected. Examples of such wavelengths of red light include 805 nm and 940 nm.

[0140] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit infrared light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the infrared light that has passed through biological tissue. The input interface 41 receives the signal S1.

[0141] The processor 43 acquires the change over time of the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. As a result, the change over time of the intensity of the signal S1 acquired in this manner becomes as shown in FIG. 5. The processor 43 acquires the value of the fourth gradient G4. The processor 43 repeats this operation to acquire a plurality of values ​​of the fourth gradient G4. The processor 43 acquires the change over time of the fourth gradient G4 as a feature amount.

[0142] It is known that when a patient develops sepsis, a delay of one hour in administering antibiotics increases the mortality rate by 7%. Therefore, it is important to detect the onset of sepsis early and intervene. However, the onset process of sepsis is complex and progresses quickly, making it difficult to detect early.

[0143] The change over time of the fourth gradient G4 can be used to estimate septic shock symptoms. When the subject is in a warm shock state, the refilling speed of the arterial blood after the compression operation is released increases relatively. Therefore, the value of the fourth gradient G4 becomes smaller (the negative gradient becomes steeper). On the other hand, when the subject is in a cold shock state, the refilling speed of the arterial blood after the compression operation is released decreases relatively. Therefore, the value of the fourth gradient G4 becomes larger (the negative gradient becomes gentler). In other words, the progress of septic shock symptoms can be estimated by monitoring the increase and decrease over time of the value of the fourth gradient G4 acquired through multiple compression operations. The change over time of the fourth gradient G4 is an example of the change over time of the amount of change in the intensity of infrared light per predetermined time after the compression operation is released.

[0144] The processor 43 outputs a notification signal S3 corresponding to the change over time of the fourth gradient G4 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a graph showing the change over time of the fourth gradient G4 can be displayed on a display device. Alternatively, when the value of the fourth gradient G4 exceeds or falls below a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0145] According to this configuration, the user can estimate the septic shock symptom of the subject through the notification based on the change over time of the fourth gradient G4. The septic shock symptom is an example of a pathological condition.

[0146] Instead of outputting the notification signal S3 corresponding to the change over time of the fourth gradient G4, the processor 43 may output a notification signal S4 corresponding to an inferred result of a septic shock symptom. For example, the processor 43 is configured to infer that the subject is in a warm shock state when the fourth gradient G4 falls below a predetermined threshold, and to infer that the subject is in a cold shock state when the fourth gradient G4 exceeds the predetermined threshold.

[0147] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an audible notification, and a tactile notification. For example, a suitable indicator indicating that a septic shock symptom is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0148] Example 10: Estimation of septic shock symptoms In this example, the light-emitting unit 10 includes a light source that emits infrared light. The wavelength of the infrared light is determined so that the difference between the absorbance due to oxygenated hemoglobin and the absorbance due to deoxygenated hemoglobin in blood is smaller than a predetermined value. In other words, a wavelength whose absorbance is not easily affected by changes in oxygenation state is selected. Examples of such wavelengths of red light include 805 nm and 940 nm.

[0149] The processor 43 outputs a control signal S2 for causing the light-emitting unit 10 to emit infrared light from the output interface 42. The light-receiving unit 20 outputs a signal S1 corresponding to the received light intensity of the infrared light that has passed through biological tissue. The input interface 41 receives the signal S1.

[0150] The processor 43 acquires the change over time of the intensity of the signal S1 while causing the compression control unit 44 to control the compression operation by the compression device 30. As a result, the change over time of the intensity of the signal S1 acquired in this manner becomes as shown in (A) of FIG.

[0151] Processor 43 obtains a correlation value between a waveform factor of a pulse wave superimposed on signal S1 before a compression operation is performed and a waveform factor of a pulse wave superimposed on signal S1 after the compression operation is performed. Examples of the correlation value include a difference value or a ratio. Specifically, processor 43 obtains a correlation value for waveform factors of the same type among the multiple waveform factors described with reference to FIG. 4B. For example, when focusing on amplitude Ap, processor 43 obtains a difference value (Ap1-Ap2) or a ratio (Ap1 / Ap2) as the correlation value.

[0152] The processor 43 repeats the above operations to obtain a plurality of correlation values, and obtains, as a feature, the change over time in the correlation values.

[0153] The change in the correlation value over time can be used to estimate septic shock symptoms. The change in the correlation value over time is an example of a change in the correlation value over time between the form factor of a pulse wave superimposed on the intensity change of infrared light before a compression is performed and the form factor of a pulse wave superimposed on the intensity change of infrared light after a compression is performed.

[0154] In a warm shock state, the dilatation ability of peripheral blood vessels is enhanced. In this case, blood vessels dilate after the compression operation is released, and the value of Ap2 increases. This causes the difference value (Ap1-Ap2) to decrease. On the other hand, in a cold shock state, the dilatation ability of peripheral blood vessels decreases. In this case, blood vessels do not dilate as easily after the compression operation is released, and the difference value (Ap1-Ap2) increases. In other words, if there is a change over time such that the difference value (Ap1-Ap2) increases, a decrease in the dilatation ability of peripheral blood vessels or a transition to a cold shock state can be estimated as an example of a septic shock symptom.

[0155] The processor 43 outputs a notification signal S3 corresponding to the change over time of the correlation value from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a graph showing the change over time of the correlation value can be displayed on a display device. Alternatively, when the correlation value exceeds or falls below a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0156] According to this configuration, the user can estimate the septic shock symptoms of the subject through the notification based on the change over time of the correlation value. The septic shock symptoms are an example of a pathological condition.

[0157] Instead of outputting the notification signal S3 corresponding to the change over time of the correlation value, the processor 43 may output a notification signal S4 corresponding to an inferred result of the septic shock symptom. For example, the processor 43 is configured to infer that the subject is transitioning to a cold shock state.

[0158] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an audible notification, and a tactile notification. For example, a suitable indicator indicating that a septic shock symptom is suspected may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0159] Example 11: Estimation of transition to cold shock state In this example, the light emitting unit 10 includes a first light source that emits red light and a second light source that emits infrared light. The wavelengths of the red light and the infrared light are determined so that they are absorbed by hemoglobin in blood at different levels. An example of the wavelength of the red light is 660 nm. An example of the wavelength of the infrared light is 940 nm.

[0160] The processor 43 outputs a control signal S2 from the output interface 42, which causes the light-emitting unit 10 to alternately emit red light and infrared light. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of red light that has passed through biological tissue and a signal S12 corresponding to the received light intensity of infrared light that has passed through biological tissue. The input interface 41 alternately receives the signals S11 and S12. The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12, while causing the compression control unit 44 to control the compression operation by the compression device 30.

[0161] In the same manner as in Example 1, the processor 43 obtains a difference value between the intensity of the signal S11 and the intensity of the signal S12. As a result, the change over time of the difference value becomes as illustrated in FIG. 2B. The difference value between the intensity of the signal S11 and the intensity of the signal S12 is an example of a first correlation value. Another example of the first correlation value is the ratio of the intensity of the signal S11 to the intensity of the signal S12.

[0162] The processor 43 acquires a difference value D21 (=d2-d1) between the difference value d1 at time t1 and the difference value d2 at time t2 as a feature. The difference value d1 is an example of a first correlation value before the compression operation by the compression device 30 is performed. The difference value d2 is an example of a first correlation value after the compression operation by the compression device 30 is performed. The difference value D21 is an example of a second correlation value.

[0163] The processor 43 further acquires a fourth gradient G4 as a feature amount. The definition of the fourth gradient G4 is in accordance with the definition of the fourth gradient G4 described with reference to Fig. 5. The fourth gradient G4 is an example of the amount of change in the first correlation value per predetermined time after the compression motion is released.

[0164] As another example of the first correlation value, the ratio between the intensity of the signal S11 and the intensity of the signal S12 may be obtained. In this case, as another example of the second correlation value, the difference between the ratio at time t1 and the ratio at time t2 is obtained.

[0165] As the warm shock state transitions to the cold shock state, blood flow in peripheral tissues cannot be maintained, leading to insufficient oxygen supply to the peripheral tissues. This can lead to multiple organ failure. Therefore, it is important to detect the change in the shock state early and intervene in treatment. However, the transition process to the shock state is complex and progresses quickly, making it known that early detection is difficult.

[0166] The difference value D21 and the fourth gradient G4 can be used to estimate a transition to a cold shock state. As the transition to a cold shock state accompanies insufficient oxygen supply to peripheral tissues, the oxygen saturation of the arterial blood removed by the compression action decreases. In this case, the intensity of the signal S12 increases, so the difference value D21 decreases. On the other hand, the blood flow supplied to the peripheral tissues decreases, so the value of the fourth gradient G4 increases (the negative gradient becomes gentler).

[0167] The processor 43 outputs a notification signal S3 corresponding to the difference value D21 and the fourth gradient G4 from the output interface 42. The notification unit 49 can provide notification based on the notification signal S3. The notification based on the notification signal S3 can be provided using at least one of visual notification, auditory notification, and tactile notification. For example, an indicator indicating the difference value D21 and an indicator indicating the fourth gradient G4 can be displayed on a display device. Alternatively, when the difference value D21 falls below a predetermined threshold and the fourth gradient G4 exceeds a predetermined threshold, an appropriate indicator can be displayed or an alarm sound can be output. The notification based on the notification signal S3 can be provided by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0168] According to this configuration, the user can estimate that the subject is transitioning to a cold shock state through the notification based on the difference value D21 and the fourth gradient G4. The transition to a cold shock state is an example of a pathological condition.

[0169] Instead of outputting the notification signal S3 corresponding to the difference value D21 and the fourth gradient G4, the processor 43 may output a notification signal S4 corresponding to an estimation result of a transition to a cold shock state. In this case, the processor 43 is configured to estimate that the subject is transitioning to a cold shock state when the difference value D21 falls below a predetermined threshold and the fourth gradient G4 exceeds a predetermined threshold.

[0170] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an audible notification, and a tactile notification. For example, a suitable indicator may be displayed to indicate that a transition to a cold shock state is occurring, or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0171] Example 12: Estimation of impaired oxygen utilization in biological tissues In this example, the light emitting unit 10 includes a first light source that emits red light and a second light source that emits infrared light. The wavelengths of the red light and the infrared light are determined so that they are absorbed by hemoglobin in blood at different levels. An example of the wavelength of the red light is 660 nm. An example of the wavelength of the infrared light is 940 nm.

[0172] The processor 43 outputs a control signal S2 from the output interface 42, which causes the light-emitting unit 10 to alternately emit red light and infrared light. The light-receiving unit 20 alternately outputs a signal S11 corresponding to the received light intensity of red light that has passed through biological tissue and a signal S12 corresponding to the received light intensity of infrared light that has passed through biological tissue. The input interface 41 alternately receives the signals S11 and S12. The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12, while causing the compression control unit 44 to control the compression operation by the compression device 30.

[0173] In the same manner as in Example 1, the processor 43 obtains a difference value between the intensity of the signal S11 and the intensity of the signal S12. As a result, the change over time of the difference value becomes as illustrated in FIG. 2B. The difference value between the intensity of the signal S11 and the intensity of the signal S12 is an example of a first correlation value. Another example of the first correlation value is the ratio of the intensity of the signal S11 to the intensity of the signal S12.

[0174] The processor 43 acquires a difference value D21 (=d2-d1) between the difference value d1 at time t1 and the difference value d2 at time t2 as a feature. The difference value d1 is an example of a first correlation value before the compression operation by the compression device 30 is performed. The difference value d2 is an example of a first correlation value after the compression operation by the compression device 30 is performed. The difference value D21 is an example of a second correlation value.

[0175] The processor 43 further acquires a fourth gradient G4 as a feature amount. The definition of the fourth gradient G4 is in accordance with the definition of the fourth gradient G4 described with reference to Fig. 5. The fourth gradient G4 is an example of the amount of change in the first correlation value per predetermined time after the compression motion is released.

[0176] As another example of the first correlation value, the ratio between the intensity of the signal S11 and the intensity of the signal S12 may be obtained. In this case, as another example of the second correlation value, the difference between the ratio at time t1 and the ratio at time t2 is obtained.

[0177] In this example, in addition to the compression device 30, a blood flow blocking device 50 is attached to the subject. The blood flow blocking device 50 is attached, for example, to the base of the finger of the subject on which the compression device 30 is attached. The blood flow blocking device 50 may include a cuff that compresses the biological tissue by air pressure, an actuator that compresses the biological tissue by a movable member, and the like.

[0178] The compression strength can be determined as a pressure sufficiently higher than the arterial blood pressure in the biological tissue. When a cuff is used, the air pressure can be, for example, 300 mmHg. When an actuator is used, the pressing force can be, for example, 500 gf. This prevents blood from flowing in and out of the biological tissue compressed by the compression device 30.

[0179] The compression control unit 44 is configured to change at least one of the amount of blood flowing into the biological tissue and the amount of blood flowing out of the biological tissue by controlling the compression operation by the blood flow blocking device 50 attached to the subject's body. In the following description, the compression operation by the blood flow blocking device 50 is referred to as a blood flow blocking operation.

[0180] When the blood flow blocking device 50 includes a cuff, the compression control unit 44 may include a pump and a valve for adjusting the air pressure in the cuff. When the blood flow blocking device 50 includes an actuator, the compression control unit 44 may include a circuit for outputting a control signal for adjusting the displacement amount of the actuator. In this case, the control signal may be output from the output interface 42. The operation of the compression control unit 44 may be controlled by the processor 43.

[0181] The processor 43 acquires the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12 while causing the compression control unit 44 to control the blood flow blocking operation by the blood flow blocking device 50. Fig. 7 illustrates the change over time in the intensity of the signal S11 and the change over time in the intensity of the signal S12 acquired in this manner.

[0182] Reference t10 indicates the time when the blood flow blocking operation by the blood flow blocking device 50 is started. Since oxygen in the blood is consumed in a state where the inflow and outflow of blood to and from the living tissue is blocked due to compression, the concentration of deoxygenated hemoglobin increases and the concentration of oxygenated hemoglobin decreases. At this time, the absorption of red light increases, so the intensity of signal S11 decreases, and the absorption of infrared light decreases, so the intensity of signal S12 increases.

[0183] Reference t20 indicates the time point when the blood flow blocking operation by the blood flow blocking device 50 is released. As blood flows into the biological tissue with the release of compression, the intensities of the signals S11 and S12 each recover to the intensities before compression.

[0184] The processor 43 obtains a difference value between the intensity of the signal S11 and the intensity of the signal S12 even during the blood flow blocking operation by the blood flow blocking device 50. The processor 43 obtains, as a feature amount, an amount of change in the difference value per predetermined time during the blood flow blocking operation.

[0185] It is known that when anaerobic metabolism is enhanced in sepsis patients, the patient falls into an oxygen utilization disorder in which aerobic metabolism does not recover even when peripheral circulation improves and oxygen supply is sufficient. It has been proposed that in order to treat oxygen utilization disorder, it is not enough to simply maintain circulatory conditions or administer oxygen, but it is also necessary to improve metabolic function.

[0186] The difference value D21, the fourth gradient G4, and the change amount per predetermined time of the difference value between the intensity of the signal S11 and the intensity of the signal S12 during the blood flow blocking operation can be used to estimate oxygen utilization disorder in biological tissue. When aerobic metabolism is performed normally during the blood flow blocking operation, the change in intensity of the signal S11 and the change in intensity of the signal S12 show the behavior exemplified in FIG. 7. On the other hand, when aerobic metabolism is not performed normally during the blood flow blocking operation, both the change in intensity of the signal S11 and the change in intensity of the signal S12 become small. Therefore, the change amount per predetermined time of the difference value between the two also decreases. When the difference value D21 and the fourth gradient G4 acquired through the compression operation by the compression device 30 are normal values, but the change amount per predetermined time of the difference value between the intensity of the signal S11 and the intensity of the signal S12 falls below a predetermined threshold, oxygen utilization disorder in biological tissue is estimated.

[0187] The processor 43 outputs a notification signal S3 corresponding to these feature quantities from the output interface 42. The notification unit 49 may perform notification based on the notification signal S3. The notification based on the notification signal S3 is performed using at least one of visual notification, auditory notification, and tactile notification. For example, an indicator indicating each feature quantity may be displayed on a display device. Alternatively, when the difference value D21 and the fourth gradient G4 are normal values ​​and the change amount of the difference value between the intensity of the signal S11 and the intensity of the signal S12 per predetermined time falls below a predetermined threshold, an appropriate indicator may be displayed or an alarm sound may be output. The notification based on the notification signal S3 may be performed by a device remote from the medical photometer 40. In this case, the notification signal S3 is transmitted to the remote device through the output interface 42.

[0188] According to this configuration, the user can estimate the oxygen utilization disorder in the biological tissue of the subject through the notification based on these feature amounts. The oxygen utilization disorder is an example of a physiological state or a pathological condition of the biological tissue.

[0189] Instead of outputting the notification signal S3 corresponding to these feature amounts, the processor 43 may output a notification signal S4 corresponding to an estimation result of oxygen utilization impairment in biological tissues of the subject. In this case, the processor 43 is configured to estimate oxygen utilization impairment in biological tissues of the subject when the difference value D21 and the fourth gradient G4 are normal but the change rate of the difference value between the intensities of the signals S11 and S12 per predetermined time period falls below a predetermined threshold.

[0190] The notification unit 49 may issue a notification based on the notification signal S4. The notification based on the notification signal S4 may be issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator may be displayed to indicate that oxygen utilization disorder in the living tissue is suspected, or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0191] 1, the processor 43 may be configured to estimate at least one of a pathological condition of the subject and a physiological state of the biological tissue using a classifier 431. The classifier 431 is a name for a processing algorithm executed by the processor 43.

[0192] The classifier 431 is configured through prior machine learning. The teacher data used for machine learning is formed by acquiring the relationship between input and output from a plurality of subjects. The input is a time-dependent change in the signal input to the input interface 41 accompanying the compression operation by the compression device 30 performed on each subject. The output is at least one of the pathological condition and the physiological state of the living tissue of each subject obtained as a result of focusing on a predetermined feature amount in the input. As the predetermined feature amount, those described with reference to the above examples 1 to 12 can be used. Therefore, at least one of the pathological condition and the physiological state of the living tissue can also be those described with reference to the above examples 1 to 12.

[0193] As an example, a case will be described where the processor 43 performs the estimation according to the above example 4 using a classifier. The feature amount is the difference value I31 exemplified in FIG. 3. The estimation target is edema. The classifier 431 is configured to determine the likelihood corresponding to the possibility that the subject providing the signal S1 currently input to the input interface 41 has edema through machine learning using the difference value I31 in the signal S1 acquired from the subject with edema and the difference value I31 in the signal S1 acquired from the subject without edema as training data. The classifier may be, for example, a support vector machine (SVM). In this case, the likelihood is calculated as an SVM score.

[0194] Specifically, the processor 43 obtains a difference value I31 of the signal S1 and inputs it to the classifier 431. The classifier 431 calculates an SVM score for the input difference value I31. If the calculated SVM score is equal to or greater than a predetermined value, the processor 43 estimates that the subject who provided the signal S1 is highly likely to have edema.

[0195] The processor 43 outputs a notification signal S4 corresponding to the estimated edema result. The notification unit 49 issues a notification based on the notification signal S4. The notification based on the notification signal S4 is issued using at least one of a visual notification, an auditory notification, and a tactile notification. For example, a suitable indicator indicating that edema is estimated may be displayed or an alarm sound may be output. The notification based on the notification signal S4 may be issued by a device remote from the medical photometer 40. In this case, the notification signal S4 is transmitted to the remote device via the output interface 42.

[0196] According to this configuration, the processor 43 can perform empirical estimation of at least one of the pathological condition of the subject and the physiological state of the biological tissue through machine learning using data previously acquired from multiple subjects. In this case, the flexibility of the system can be increased compared to strict rule-based estimation.

[0197] As another example of a classifier that identifies whether a desired estimation result is applicable or not, logistic regression may be used. When multiple feature values ​​are used for estimation as in the above examples 11 and 12, perceptrons, decision trees, random forests, etc. may be used as classifiers.

[0198] The teacher data used for the machine learning of the classifier 431 may include clinical data of each subject. The clinical data may include at least one of age, sex, height, weight, medical history data, vital data, biochemical test data, blood test data, administered drug data, artificial respirator settings, dialysis machine settings, extracorporeal circulator settings, severity score, and the like. The vital data may include at least one of heart rate, respiratory rate, blood pressure, arterial blood oxygen saturation, exhaled carbon dioxide concentration, and the like. The severity score may include at least one of SOFA (Sequential Organ Failure Assessment) score, qSOFA (quick SOFA) score, APACHE (Acute Physiology and Chronic Health Evaluation) score, SAPS (Simplified Acute Physiology Score), and the like. In the above example, the clinical data of a subject with edema is associated with the difference value I31 in the signal S1 acquired from the subject with edema. Similarly, the clinical data of the subject is associated with the difference value I31 in the signal S1 acquired from the subject without edema.

[0199] In this case, the processor 43 is configured to refer to clinical information of the subject when estimating at least one of the pathological condition of the subject and the physiological state of the biological tissue using the identifier 431. As illustrated in Fig. 1, at least a part of the clinical information C may be input to the input interface 41 from an external sensor or medical device. In addition to or instead of this, at least a part of the clinical information C may be stored in a storage 46 built into the medical photometer 40. The storage 46 is a storage device realized by a semiconductor memory or a hard disk device.

[0200] That is, the processor 43 uses the clinical information C to calculate the SVM score. For example, when a specific vital data shows a high tendency in teacher data acquired from a plurality of subjects with edema, and the value of the vital data acquired from the current subject is high, the SVM score corresponding to the possibility of edema is calculated to be higher. With this configuration, it is possible to improve the accuracy of estimation compared to the case where only the feature amount is input to the classifier 431.

[0201] The processor 43 having the functions described above may be realized by a general-purpose microprocessor operating 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 RAM and a ROM. In this case, the ROM may store a computer program that executes the above-mentioned processing. The processor 43 specifies at least a part of the computer program stored in the ROM, deploys it on the RAM, and executes the above-mentioned processing in cooperation with the RAM. A part of the storage 46 may be used as the above-mentioned general-purpose memory. The processor 43 may be realized by a dedicated integrated circuit such as a microcontroller, an ASIC, or an FPGA that can execute a computer program that realizes the above-mentioned processing. The processor 43 may be realized by a combination of a general-purpose microprocessor and a dedicated integrated circuit.

[0202] 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.

[0203] It has been described with reference to Fig. 5 that each of the first gradient G1, the second gradient G2, the third gradient G3, the fourth gradient G4, and the fifth gradient G5 can be a feature amount. However, each of the first period T1, the second period T2, the third period T3, the fourth period T4, and the fifth period T5 used to define these gradients can also be a feature amount. For example, a smaller value of the fifth gradient G5 (a steeper negative gradient) corresponds to a shorter fifth period T5.

[0204] The location where the compression device 30 is attached is not limited to the subject's fingertip. For example, the compression device 30 may be attached to the subject's forearm. In this case, the light receiving unit 20 may be configured to receive light emitted from the light emitting unit 10 and reflected by biological tissue. In this case, the blood flow blocking device 50 may be attached to the subject's upper arm. [Explanation of symbols]

[0205] 30: compression device, 40: medical photometer, 41: input interface, 42: output interface, 43: processor, 431: discriminator, 44: compression control unit, 50: blood flow blocking device, S1, S11, S12: signals corresponding to the intensity of light passing through biological tissue, S3: notification signal, S4: notification signal, C: clinical information

Claims

1. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating intraperitoneal bleeding of the subject from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light includes first infrared light having a difference between an absorbance by oxygenated hemoglobin and an absorbance by deoxygenated hemoglobin that is smaller than a predetermined value, and second infrared light having a greater absorbance by water than by hemoglobin; the processor acquires a first correlation value between the intensity of the first infrared light and the intensity of the second infrared light, and acquires, as the feature, a second correlation value corresponding to a correlation between the first correlation value before the compressing motion is performed and the first correlation value after the compressing motion is performed; Medical photometer.

2. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating a pathological condition in which an oxygenation state of a capillary bed of the subject is decreased from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is red light in which a difference between an absorbance by oxygenated hemoglobin and an absorbance by deoxygenated hemoglobin is greater than a predetermined value; The processor acquires, as the feature amount, a correlation value between an intensity of the red light before the compression motion is performed and an intensity of the red light after the compression motion is released. Medical photometer.

3. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating edema of the subject from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light that is absorbed more by water than by hemoglobin; The processor acquires, as the feature amount, an area under a waveform obtained by a change over time in the intensity of the infrared light after the compression motion is released. Medical photometer.

4. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating a pathological condition in which a vascular endothelial function of the subject is impaired from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, a correlation value between an intensity of the infrared light before the compressing motion is performed and an intensity of the infrared light after the compressing motion is performed. Medical photometer.

5. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating a pathological condition in which a vascular endothelial function of the subject is impaired from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, an area under a waveform obtained by a change over time in the intensity of the infrared light after the compression motion is released. Medical photometer.

6. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating at least one of a pathological condition of the subject and a physiological state of the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, a correlation value between a form factor of a pulse wave superimposed on the intensity change of the infrared light before the compression motion is performed and a form factor of a pulse wave superimposed on the intensity change of the infrared light after the compression motion is performed. Medical photometer.

7. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor that acquires a feature amount used to estimate a sign of shock, which is a drop in blood pressure of the subject, from a time-dependent change in the signal accompanying the compressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, an amount of change in intensity of the infrared light per predetermined time after the pressing motion is released. Medical photometer.

8. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating an oxygen metabolic state in the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface for outputting a signal corresponding to a result of the estimation; the light being red light and infrared light that are absorbed by hemoglobin to different degrees, The processor obtains a correlation value between the intensity of the red light and the intensity of the infrared light, and obtains, as the feature amount, an amount of change in the correlation value per predetermined time after the pressing motion is released. Medical photometer.

9. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating at least one of a pathological condition of the subject and a physiological state of the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light includes first infrared light having a difference between an absorbance by oxygenated hemoglobin and an absorbance by deoxygenated hemoglobin that is smaller than a predetermined value, and second infrared light having a greater absorbance by water than by hemoglobin; the processor acquires, as the feature amount, a shape factor of a locus of points determined by the intensity of the first infrared light and the intensity of the second infrared light on a coordinate plane formed by a first coordinate axis corresponding to the intensity of the first infrared light and a second coordinate axis corresponding to the intensity of the second infrared light; Medical photometer.

10. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor that acquires a feature amount used to estimate a septic shock symptom of the subject from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, a time-dependent change in an amount of change in intensity of the infrared light per predetermined time after the pressing motion is released. Medical photometer.

11. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating at least one of a pathological condition of the subject and a physiological state of the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light is infrared light having a difference between an absorbance of oxygenated hemoglobin and an absorbance of deoxygenated hemoglobin that is less than a predetermined value; The processor acquires, as the feature amount, a change over time in a correlation value between a form factor of a pulse wave superimposed on the intensity change of the infrared light before the compression motion is performed and a form factor of a pulse wave superimposed on the intensity change of the infrared light after the compression motion is performed. Medical photometer.

12. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating a transition of the subject to a cold shock state from a time-dependent change in the signal accompanying the pressing motion; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, the light being red light and infrared light that are absorbed by hemoglobin to different degrees, The processor obtains a first correlation value between the intensity of the red light and the intensity of the infrared light, and calculates, as the feature amount, a second correlation value corresponding to a correlation between the first correlation value before the compressing motion and the first correlation value after the compressing motion is performed; and a change amount of the first correlation value per predetermined time after the compression motion is released. Medical photometer.

13. an input interface for receiving a signal corresponding to the intensity of light passing through biological tissue of a subject; a compression control unit that controls a compression operation by a compression device attached to the body of the subject to change at least one of a thickness of the biological tissue, an amount of blood contained in the biological tissue, an amount of interstitial fluid contained in the biological tissue, an amount of blood flowing into the biological tissue, and an amount of blood flowing out of the biological tissue; a processor for acquiring a feature amount used for estimating oxygen utilization impairment in the biological tissue from a time-dependent change in the signal accompanying the pressing operation; an output interface that outputs a signal corresponding to the feature amount or a result of the estimation, The compression control unit is capable of controlling a blood flow blocking operation of a blood flow blocking device that blocks blood flow into the biological tissue by compression, the light being red light and infrared light that are absorbed by hemoglobin to different degrees, The processor obtains a first correlation value between the intensity of the red light and the intensity of the infrared light, and calculates, as the feature amount, a second correlation value corresponding to a correlation between the first correlation value before the compressing motion and the first correlation value after the compressing motion is performed; A change amount of the first correlation value per predetermined time after the pressing action is released; and a change amount of the first correlation value per predetermined time during the blood flow blocking operation; and Get Medical photometer.

14. 14. The medical photometer according to claim 1, wherein the processor performs the estimation using a classifier that has learned a relationship between a feature amount in the signal acquired from each of a plurality of subjects and a target of the estimation as training data.

15. The teacher data includes clinical information of each of the plurality of subjects, The processor performs the estimation.

15. The medical photometer of claim 14.

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