JP7732291B2 - Biological information measuring device and biological information measuring program - Google Patents

Description

The present invention relates to a biological information measurement device and a biological information measurement program.

Patent Document 1 discloses a biological information measuring device equipped with a notification means that sends a notification to a subject who has stopped breathing to restart breathing when a specified time that defines the period of breathing has been reached, and a measurement means that measures the oxygen circulation time, which indicates the time it takes for oxygen taken into the subject's body upon the resumption of breathing to reach a predetermined site.

Japanese Patent Application Laid-Open No. 2019-166147

Until now, when measuring oxygen circulation time multiple times using a bioinformation measurement device, changes in blood oxygen saturation were measured until a predetermined measurement time had elapsed before the next measurement was performed. Therefore, to measure oxygen circulation time three times, the time required to measure oxygen circulation time once multiplied by 3 was required.

The technology disclosed herein aims to provide a biological information measurement device and a biological information measurement program that, when measuring oxygen circulation time multiple times, can shorten the time required to measure oxygen circulation time multiple times compared to starting the next measurement of oxygen circulation time after the end of a predetermined measurement period of oxygen circulation time.

The biological information measurement device according to the first aspect includes a processor, and when measuring oxygen circulation time a predetermined number of times, the processor notifies the subject of oxygen circulation time measurement to stop breathing, a preparatory action for measuring oxygen circulation time in the next measurement, before the end of the measurement period of the predetermined oxygen circulation time in the previous measurement.

The biological information measuring device according to the second aspect is the biological information measuring device according to the first aspect, in which the processor varies the breathing adjustment time, which is the period from when the subject is instructed to resume breathing after stopping breathing until when the subject is instructed to stop breathing again in order to measure the oxygen circulation time in the next measurement, depending on the measurement status of the oxygen circulation time of the subject.

A biological information measuring device according to a third aspect is the biological information measuring device according to the second aspect, wherein the processor controls the breathing adjustment time so that the breathing adjustment time becomes longer as the measurement of the oxygen circulation time of the subject approaches the final measurement.

In the fourth aspect of the biological information measuring device, in the second aspect, the processor controls the breathing adjustment time to be the period from when the subject, who has stopped breathing, is instructed to resume breathing until an inflection point is detected at which the subject's blood oxygen saturation changes from decreasing to increasing as the subject resumes breathing.

A biological information measuring device according to a fifth aspect is the biological information measuring device according to the fourth aspect, wherein the processor controls the final oxygen circulation time measurement for the subject so that the measurement of the oxygen circulation time is not terminated until the inflection point is detected.

In a sixth aspect of the biological information measuring device, in the biological information measuring device according to any one of the first to fifth aspects, the processor controls the breathing hold time, which is the period from when the subject is instructed to stop breathing until when the subject is instructed to resume breathing, to shorten the breathing hold time as the measurement of the subject's oxygen circulation time approaches the final measurement.

A seventh aspect of the biological information measuring device is a biological information measuring device according to any one of the first to fifth aspects, in which the processor varies the breath-hold time, which is the period from when the subject is instructed to stop breathing to when the subject is instructed to resume breathing, depending on the difference between the lowest oxygen saturation value in the subject's blood and a predetermined oxygen saturation reference value that defines the lowest oxygen saturation value required for measuring oxygen circulation time.

The biological information measuring device according to the eighth aspect is the biological information measuring device according to the seventh aspect, wherein the processor shortens the breath-hold time as the difference increases when the minimum value is equal to or less than the reference value, and lengthens the breath-hold time as the difference increases when the minimum value exceeds the reference value.

The biological information measurement program according to the ninth aspect is a program for causing a computer to execute a process for notifying a subject whose oxygen circulation time is being measured to stop breathing, a preparatory action for measuring oxygen circulation time in the next measurement, before the end of the measurement period of the oxygen circulation time in the previous measurement, when the oxygen circulation time is measured a predetermined number of times.

The first and ninth aspects have the advantage that, when measuring the oxygen circulation time multiple times, the time required to measure the oxygen circulation time multiple times can be shortened compared to when the next measurement of the oxygen circulation time is started after the end of a predetermined measurement period of the oxygen circulation time.

The second aspect has the advantage of being able to shorten the time required to measure oxygen circulation time multiple times, compared to when a common breathing adjustment time is used for each measurement.

The third aspect has the effect of reducing the burden on the subject involved in measuring oxygen circulation time.

The fourth aspect has the advantage that, compared to measuring oxygen circulation time using a breathing adjustment time that is set regardless of the change in the subject's oxygen saturation, a breathing adjustment time can be set for each subject according to the change characteristics of the subject's oxygen saturation.

The fifth aspect has the advantage of being able to improve measurement accuracy in the final oxygen circulation time measurement, compared to when oxygen saturation measurement is terminated upon the end of a predetermined oxygen saturation observation period.

The sixth aspect has the advantage of reducing the burden on the subject associated with measuring oxygen circulation time compared to when a common breath-holding period is used for each measurement.

The seventh aspect has the advantage of being able to vary the breath-holding time.

The eighth aspect has the advantage of improving the accuracy of measuring oxygen circulation time while reducing the burden on the subject, compared to when the breath-holding time is set in advance.

FIG. 1 is a schematic diagram showing an example of measurement of blood oxygen saturation. 10 is a graph showing an example of changes in the amount of light absorbed by a living body. FIG. 2 is a diagram showing an example of the amount of light absorbed by oxygenated hemoglobin and reduced hemoglobin at each wavelength. FIG. 1 is a diagram illustrating an example of the configuration of a biological information measuring device. 1A and 1B are diagrams illustrating examples of the arrangement of light-emitting elements and light-receiving elements. 10A and 10B are diagrams illustrating other examples of the arrangement of light-emitting elements and light-receiving elements. FIG. 10 is a diagram showing an example of changes in blood oxygen saturation. FIG. 2 is a diagram illustrating an example of the configuration of a main part of an electrical system in the biological information measuring device. 10 is a flowchart illustrating the first half of an example of the flow of a biological information measurement process according to the first and second embodiments. 10 is a flowchart illustrating the second half of an example of the flow of the biological information measurement process according to the first embodiment. 10 is a graph showing an example of time variation in the oxygen saturation of a subject when the biological information measurement process according to the first embodiment is executed. 10 is a graph showing an example of the change over time in the oxygen saturation of a subject when the first LFCT measurement and the second LFCT measurement are not performed overlappingly. 10 is a flowchart illustrating the second half of an example of the flow of a biological information measurement process according to the second embodiment. 10 is a graph showing an example of the change in the oxygen saturation level of a subject over time in the final LFCT measurement when an inflection point in the oxygen saturation level of the subject is detected before the elapse of the follow-up observation time. 10 is a graph showing an example of the change over time in the oxygen saturation of a subject in the final LFCT measurement, in which an inflection point in the subject's oxygen saturation is detected after the elapse of a follow-up observation period. 10 is a diagram illustrating an example of the relationship between an inflection point of oxygen saturation and a reference value of oxygen saturation. FIG.

This embodiment will now be described with reference to the drawings. Note that the same components and processes will be assigned the same reference numerals throughout the drawings, and duplicate explanations will be omitted.

First Embodiment
The biological information measuring device 10 is a device that measures biological information, particularly biological information related to the circulatory system, among information (biological information) related to a living body 8. The circulatory system is a general term for a group of organs that circulate and transport body fluids, such as blood, within the body.

There are multiple indicators of biological information related to the circulatory system, but one indicator that shows the condition of the heart, which pumps blood into the blood vessels, is cardiac output (CO), which represents the amount of blood pumped from the heart.

It is known that if cardiac output drops below the reference value, there is a suspicion of left heart failure, and if cardiac output increases above the reference value, there is a suspicion of right heart failure. Cardiac output is used to test for various heart diseases or to confirm the effectiveness of medication.

One method for measuring cardiac output is to insert a catheter with a balloon at its tip into the pulmonary artery of the subject whose cardiac output is being measured, measure blood oxygen saturation while inflating and deflating the balloon, and calculate cardiac output from the measured oxygen saturation. Blood oxygen saturation is an example of an index of blood oxygen concentration, and is an index of the degree to which hemoglobin in the blood is bound to oxygen. A decrease in blood oxygen saturation indicates a greater likelihood of developing symptoms such as anemia. Like cardiac output, blood oxygen saturation is also an example of biometric information, and is used as an index of the subject's ability to take in oxygen. Hereinafter, blood oxygen saturation will be simply referred to as "oxygen saturation."

Measuring oxygen saturation and cardiac output using a catheter requires the catheter to be inserted into the subject's blood vessels, which requires surgical procedures and is more invasive for the subject than other measurement methods.

Therefore, a method of measuring oxygen saturation and cardiac output from the subject's pulse wave is used, which places less strain on the subject than catheter-based measurement methods. Note that the pulse wave is an indicator of changes in the pulsation of blood vessels as the heart pumps blood.

First, referring to Figure 1, we will explain how to measure oxygen saturation, one of the vital signs.

As shown in Figure 1, oxygen saturation is measured by irradiating light from a light-emitting element 1 onto the subject's body (living body 8), receiving the light from a light-receiving element 3, and measuring the intensity of the light reflected or transmitted by arteries 4, veins 5, capillaries 6, and other vessels throughout the subject's body, i.e., the amount of reflected or transmitted light received.

Figure 2 is a conceptual diagram showing, for example, the change in the amount of light absorbed by a living organism 8. As shown in Figure 2, the amount of light absorbed by the living organism 8 tends to fluctuate over time.

Furthermore, when examining the breakdown of variations in light absorption in the living body 8, it is known that the amount of light absorption varies mainly due to the arteries 4, while the amount of variation in the veins 5 and other tissues, including stationary tissue, is such that the amount of light absorption can be considered to be unchanged compared to the arteries 4. This is because arterial blood pumped from the heart moves within the blood vessels accompanied by a pulse wave, causing the arteries 4 to expand and contract over time along the cross-sectional direction of the arteries 4, changing the thickness of the arteries 4. Note that in Figure 2, the range indicated by arrow 94 indicates the amount of variation in light absorption corresponding to changes in the thickness of the arteries 4.

In FIG. 2, if the amount of light received at time t _a is I _a and the amount of light received at time t _b is I _b , the amount of change ΔA in the amount of light absorbed due to a change in the thickness of the artery 4 is expressed by equation (1).

(Number 1)

ΔA=ln(I _b /I _a )...(1)

In contrast, Figure 3 is a diagram showing an example of the light absorption at each wavelength of hemoglobin bound to oxygen (oxyhemoglobin) and hemoglobin not bound to oxygen (reduced hemoglobin) flowing through artery 4. In Figure 3, light absorption curve 96 represents the light absorption by oxygenated hemoglobin, and light absorption curve 97 represents the light absorption by reduced hemoglobin.

As shown in Figure 3, it is known that oxygenated hemoglobin is more likely than reduced hemoglobin to absorb light in the infrared (IR) region 99, which has a wavelength around 850 nm, and that reduced hemoglobin is more likely than oxygenated hemoglobin to absorb light in the red region 98, which has a wavelength around 660 nm.

Furthermore, it is known that oxygen saturation is proportional to the ratio of the change in absorbance ΔA at different wavelengths.

Therefore, by using infrared light (IR light) and red light, which are more likely to cause a difference in light absorption between oxygenated hemoglobin and reduced hemoglobin than other wavelength combinations, and calculating the ratio between the change in light absorption ΔA _IR when IR light is irradiated onto the living body 8 and the change in light absorption ΔA _Red when red light is irradiated onto the living body 8, the oxygen saturation level S can be calculated using equation (2). Note that in (2), k is a proportionality constant.

(Number 2)

S=k(ΔA _Red /ΔA _IR )...(2)

That is, when calculating oxygen saturation, multiple light-emitting elements 1, each emitting light of a different wavelength, are irradiated onto the living body 8. Specifically, light-emitting elements 1 that emit IR light and light-emitting elements 1 that emit red light are used on the living body 8. In this case, the light-emitting elements 1 that emit IR light and the light-emitting elements 1 that emit red light may have overlapping light-emitting periods, but it is preferable that the light-emitting elements 1 do not overlap. The light reflected or transmitted by each light-emitting element 1 is then received by the light-receiving element 3, and oxygen saturation is measured by calculating equations (1) and (2), or known equations obtained by modifying these equations, from the amount of light received at each time.

As a known formula obtained by transforming the above formula (1), for example, formula (1) can be expanded to express the change in light absorption amount ΔA as formula (3).

(Number 3)

ΔA=lnI _b -lnI _a ...(3)

Furthermore, equation (1) can be transformed into equation (4).

(Number 4)

ΔA=ln(I _b /I _a )=ln(1+(I _b -I _a )/I _a ) ...(4)

Normally, since (I _b - _{I a} ) << I _a , ln(I _b / I _a ) ≒ (I _b - _{I a} ) / I _a holds, so instead of equation (1), equation (5) can be used to represent the change ΔA in the amount of light absorption.

(Number 5)

ΔA≒(I _b - I _a )/I _a ...(5)

Hereinafter, when it is necessary to distinguish between the light-emitting element 1 that emits IR light and the light-emitting element 1 that emits red light, the light-emitting element 1 that emits IR light will be referred to as "light-emitting element 1A," and the light-emitting element 1 that emits red light will be referred to as "light-emitting element 1B."

With this method, oxygen saturation is measured by bringing the light-emitting element 1 and light-receiving element 3 close to the subject's body surface, which places less strain on the subject than measuring oxygen saturation by inserting a catheter into a blood vessel.

The subject's cardiac output is calculated using the measured oxygen saturation; details of this calculation method will be explained later.

Figure 4 is a diagram showing an example configuration of the biological information measuring device 10. As shown in Figure 4, the biological information measuring device 10 includes a photoelectric sensor 11, a pulse wave processing unit 12, an oxygen saturation measurement unit 13, an oxygen circulation time measurement unit 14, a cardiac output measurement unit 15, a timer unit 16, and a notification unit 17.

The photoelectric sensor 11 includes a light-emitting element 1A that emits IR light with a central wavelength of approximately 850 nm, a light-emitting element 1B that emits red light with a central wavelength of approximately 660 nm, and a light-receiving element 3 that receives the IR light and red light.

Figure 5 shows an example of the arrangement of light-emitting element 1A, light-emitting element 1B, and light-receiving element 3 in photoelectric sensor 11. As shown in Figure 5, light-emitting element 1A, light-emitting element 1B, and light-receiving element 3 are arranged side by side facing one side of living body 8. In this case, light-receiving element 3 receives IR light and red light reflected by capillaries 6, etc., of living body 8.

However, the arrangement of the light-emitting element 1A, the light-emitting element 1B, and the light-receiving element 3 is not limited to the example arrangement shown in Figure 5. For example, as shown in Figure 6, the light-emitting element 1A and the light-emitting element 1B may be arranged opposite the light-receiving element 3, with the living body 8 in between. In this case, the light-receiving element 3 receives IR light and red light that has passed through the living body 8.

Here, as an example, light-emitting elements 1A and 1B are described as surface-emitting laser elements such as VCSELs (Vertical Cavity Surface Emitting Lasers), but they are not limited to this and may also be edge-emitting laser elements. Light-emitting elements 1A and 1B may also be LEDs (Light Emitting Diodes).

The photoelectric sensor 11 is equipped with a clip (not shown) for attaching the photoelectric sensor 11 to a part of the subject's body. The photoelectric sensor 11 is attached so that it contacts the subject's body surface with the clip (not shown) to prevent IR light and red light from leaking outside. In order to receive the IR light and red light reflected by or transmitted through the subject's living body 8 as accurately as possible using the light-receiving element 3, it is preferable to position the photoelectric sensor 11 so that it contacts the subject's body surface. However, the photoelectric sensor 11 may also be attached at a distance from the body surface as long as the IR light and red light reflected by or transmitted through the subject's living body 8 is received by the light-receiving element 3.

The photoelectric sensor 11 converts the amount of IR light and red light received by the light receiving element 3 into, for example, a voltage value and notifies the pulse wave processing unit 12.

Since a predetermined amount of light is emitted from light-emitting element 1A and light-emitting element 1B, the amount of IR light and red light absorbed by living body 8 can be obtained from the amount of IR light and red light received by photoelectric sensor 11, respectively.

The pulse wave processing unit 12 therefore uses the respective amounts of IR light and red light received from the photoelectric sensor 11 to generate a pulse wave signal representing the subject's pulse wave obtained from IR light, and a pulse wave signal representing the subject's pulse wave obtained from infrared light. The pulse wave processing unit 12 amplifies the voltage values corresponding to the respective amounts of received IR light and red light so that they fall within a predetermined range suitable for generating pulse wave signals. The pulse wave processing unit 12 then generates each pulse wave signal from which noise components have been removed using a known filter or the like. The pulse wave processing unit 12 notifies the oxygen saturation measurement unit 13 of the generated pulse wave signals.

Upon receiving the pulse wave signal from the pulse wave processing unit 12, the oxygen saturation measurement unit 13 measures the oxygen saturation of the subject from the received pulse wave signal. Specifically, the oxygen saturation measurement unit 13 uses the pulse wave signal to calculate the amount of change ΔA _IR in the amount of IR light absorbed due to a change in the thickness of the artery 4 and the amount of change ΔA _Red in the amount of red light absorbed, respectively, according to equation (1). Then, using the calculated amounts of change ΔA _IR and ΔA _Red , the oxygen saturation measurement unit 13 measures the oxygen saturation of the subject from equation (2), for example, and notifies the oxygen circulation time measurement unit 14 of the measured oxygen saturation.

Although the following description will be given as an example in which the oxygen saturation measurement unit 13 measures the oxygen saturation of the subject, the oxygen saturation measurement unit 13 may measure any value that indicates the change in the oxygen saturation of the subject over time. For example, the oxygen saturation measurement unit 13 may measure a value that correlates with the change in oxygen saturation over time, such as the reciprocal of the oxygen saturation or the ratio of the change ΔA _Red to the change ΔA _IR .

The oxygen circulation time measurement unit 14 detects the inflection point of oxygen saturation by referencing the subject's oxygen saturation measured by the oxygen saturation measurement unit 13, and measures the oxygen circulation time.

Figure 7 is a graph showing an example of changes in oxygen saturation at a specific location on the subject, with the horizontal axis representing time and the vertical axis representing oxygen saturation.

When the subject stops breathing at time _t1 , the subject's oxygen saturation begins to decrease. Even if the subject resumes breathing after the end of the breath-hold period (time _t2 ), it takes time for the oxygen taken into the blood upon resumption of breathing to reach specific areas, so the subject's oxygen saturation continues to decrease after time _t2 . Eventually, as the oxygen taken into the blood upon resumption of breathing reaches specific areas from the lungs, the subject's oxygen saturation begins to increase. The point at which oxygen saturation changes from decreasing to increasing is called the "inflection point." If the time at which the inflection point appears is designated time _t60 , the oxygen circulation time is expressed as the difference between time _t2 and time _t60 .

In other words, oxygen circulation time represents the time it takes for oxygen to be transported from the lungs to a specific area, and is also called the "oxygen delivery time."

The oxygen circulation time measured from changes in oxygen saturation tends to vary in measurement accuracy depending on the variation in the breathing hold period, so the biological information measurement device 10 pre-sets a breathing hold period T1 that defines the length of the breathing hold period.

Specifically, if the subject resumes breathing while their oxygen saturation is decreasing, the oxygen saturation may begin to increase before it has fully decreased to the minimum value required for measuring the oxygen circulation time. If the oxygen circulation time is measured from a change in oxygen saturation that has not decreased to the minimum value required for measuring the oxygen circulation time, the accuracy of the oxygen circulation time measurement will be lower than if the oxygen circulation time is measured from a change in oxygen saturation that has decreased to the minimum value required for measuring the oxygen circulation time.

Therefore, the breath-hold time T1 is set so that, for as many subjects as possible, the minimum oxygen saturation level that can be achieved by the subject ceasing breathing is lower than the minimum oxygen saturation level required to measure oxygen circulation time.

Therefore, the breath-hold time T1 is determined in advance through experiments using an actual device such as the vital signs measuring device 10.

Hereinafter, the minimum oxygen saturation value required for measuring oxygen circulation time will be referred to as the "oxygen saturation reference value H." The oxygen saturation reference value H will also be determined in advance through experiments using the actual vital signs measurement device 10.

Note that the lowest oxygen saturation value falling below the oxygen saturation reference value H means that the lowest oxygen saturation value is equal to or lower than the oxygen saturation reference value H.

The oxygen circulation time measurement unit 14 stores the time when the inflection point of the oxygen saturation is detected as time _t60 , and measures the time represented by the difference between time _t2 and time _t60 as the oxygen circulation time. Note that "detecting an inflection point" includes detecting a position within a range shifted forward or backward along the time axis from the inflection point of the oxygen saturation, as long as it does not substantially affect the measurement of the oxygen circulation time.

The oxygen circulation time measurement unit 14 notifies the notification unit 17 and the cardiac output measurement unit 15 of the measured oxygen circulation time.

The location where the oxygen circulation time is measured is determined by the attachment position of the photoelectric sensor 11 on the subject. In this embodiment, as an example, the photoelectric sensor 11 is attached to a peripheral location on the subject. More specifically, it is attached to the fingertip, and the oxygen circulation time when oxygen is transported from the lungs to the fingertip is measured. This is because the longer distance from the lungs compared to other locations results in a longer oxygen circulation time, and therefore a more accurate oxygen circulation time can be obtained compared to when the photoelectric sensor 11 is attached to other locations. Note that a "peripheral location" refers to a location on the subject's body that is more peripheral than the neck, shoulders, or hip joints.

Therefore, the oxygen circulation time from the lungs to the fingertips is sometimes referred to as LFCT (Lung to Finger Circulation Time). In this embodiment, too, an example is described in which photoelectric sensor 11 is attached to the subject's fingertips and LFCT is measured by oxygen circulation time measurement unit 14, but the attachment location of photoelectric sensor 11 is not limited to fingertips. Photoelectric sensor 11 may be attached to any part of the subject's body as long as the measurement error of the obtained oxygen circulation time falls within a predetermined range. Note that "fingertip" refers to the fingertips of the subject's hands, but photoelectric sensor 11 may also be attached to the toes.

The cardiac output measurement unit 15 measures the subject's cardiac output using the LFCT received from the oxygen circulation time measurement unit 14. The cardiac output is calculated, for example, using a predetermined equation that represents the relationship between LFCT and cardiac output.

In addition to cardiac output, the cardiac output measurement unit 15 may also measure information related to cardiac output. "Information related to cardiac output" refers to information that is correlated with cardiac output, and includes, for example, cardiac index and stroke volume.

The "cardiac index" is the value obtained by dividing the subject's cardiac output by the subject's body surface area in order to correct for differences in cardiac output due to differences in the subject's physique. Furthermore, the "stroke volume" is a value indicating the amount of blood pumped into the artery 4 by the heart with one contraction, and is calculated by dividing the cardiac output by the subject's heart rate per minute.

The cardiac output measurement unit 15 notifies the notification unit 17 of the measured cardiac output. Note that although the biological information measurement device 10 shown in FIG. 4 has a cardiac output measurement unit 15 for measuring cardiac output, measuring cardiac output is not essential for the biological information measurement device 10. Therefore, the biological information measurement device 10 does not need to include the cardiac output measurement unit 15.

The notification unit 17 notifies the subject to begin holding their breath, and also works in conjunction with the timer unit 16 to measure the breathing hold time T1, and notifies the subject to resume breathing after the breathing hold time T1 has elapsed. The timer unit 16 is equipped with a timer that measures time, and measures the time of a section with a specified start and end.

Furthermore, when measuring the oxygen circulation time of the same subject multiple times, the notification unit 17 notifies the subject to resume breathing, and then notifies the subject to resume cessation of breathing in order to measure the oxygen circulation time in the next measurement.

The period from when a subject who has stopped breathing is instructed to resume breathing until they are instructed to stop breathing again in order to measure the oxygen circulation time for the next measurement is the period during which the subject regulates their breathing in preparation for the next oxygen circulation time measurement. Therefore, hereafter, the length of this period will be referred to as the "breathing regulation time T2."

Furthermore, the notification unit 17 notifies at least one of the subject and the medical professional in charge of the subject of the oxygen circulation time measured by the oxygen circulation time measurement unit 14 and the cardiac output measured by the cardiac output measurement unit 15.

In this embodiment, "notification" refers to making instructions from or information obtained by the biological information measuring device 10 recognizable to at least one of the subject and the medical professional in charge of the subject. Therefore, ways in which the biological information measuring device 10 notifies the subject of instructions such as restarting or stopping breathing include visual notification, such as displaying the instruction on a display; auditory notification, such as issuing an instruction audibly; and contact notification, such as transmitting an instruction via vibration, to the subject. Furthermore, ways in which biological information measured by the biological information measuring device 10 is notified include visual notification, such as displaying the measured biological information on a display; auditory notification, such as issuing the measured biological information audibly; notification using a storage device, such as storing the measured biological information in a storage device to which at least one of the subject and the medical professional in charge of the subject has read permission; notification using a recording medium, such as forming the measured biological information on a recording medium such as paper using an image forming device; and notification using a communication line, such as transmitting the measured biological information to an external device via a communication line.

The above-described biological information measuring device 10 is configured using, for example, a computer. Figure 8 is a diagram showing an example of the main configuration of the electrical system of a biological information measuring device 10 configured using a computer 20.

The computer 20 includes a CPU (Central Processing Unit) 21, which processes the pulse wave processing unit 12, oxygen saturation measurement unit 13, oxygen circulation time measurement unit 14, cardiac output measurement unit 15, timer unit 16, and notification unit 17 according to this embodiment, a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, non-volatile memory 24, and an input/output interface (I/O) 25. The CPU 21, ROM 22, RAM 23, non-volatile memory 24, and I/O 25 are connected to each other via a bus 26. There are no restrictions on the operating system used by the computer 20.

Non-volatile memory 24 is an example of a storage device that maintains stored information even if the power supplied to non-volatile memory 24 is cut off, and is, for example, a semiconductor memory, but may also be a hard disk.

The I/O 25 is connected to, for example, a photoelectric sensor 11, an input unit 27, a display unit 28, and a communication unit 29.

The photoelectric sensor 11 is connected to the I/O 25 via a wired or wireless connection. The vital information measuring device 10 and the photoelectric sensor 11 may be configured as separate units, or they may be housed in the same housing, so that they are integrated.

The input unit 27 is an input device that receives instructions from, for example, the user of the biological information measuring device 10 and notifies the CPU 21. The input unit 27 includes, for example, buttons, a touch panel, a keyboard, and a mouse. The user of the biological information measuring device 10 includes, for example, the subject and the medical professional in charge of the subject.

The display unit 28 is a display device that displays information processed by the CPU 21 to the user of the biological information measurement device 10. The display unit 28 may be a display device such as a liquid crystal display, an organic electroluminescence (EL) display, or a projector.

Note that the display unit 28 is not necessarily a required unit for the biological information measurement device 10; a unit appropriate for the form of user instructions and notification of biological information is connected to the I/O 25.

For example, if instructions from the biological information measuring device 10 and measured biological information are to be notified to the user of the biological information measuring device 10 by voice, a speaker unit may be connected to the I/O 25. Also, if instructions from the biological information measuring device 10 are to be notified to the user of the biological information measuring device 10 through a physical sensation, a vibration unit may be connected to the I/O 25.

The communication unit 29 has a communication protocol that connects the vital information measurement device 10 to a communication line such as the Internet, and performs data communication between the vital information measurement device 10 and other external devices connected to the communication line. The communication unit 29 may be connected to the communication line via a wired or wireless connection. If the vital information measurement device 10 does not need to perform data communication with other external devices connected to the communication line, the communication unit 29 does not need to be connected to the I/O 25.

Note that the units connected to I/O 25 are not limited to the examples described above; other units, such as a printing unit that prints measured biometric information on a recording medium, may also be connected to I/O 25.

Next, the operation of the biological information measuring device 10 will be described using Figures 9 and 10. Below, an example will be described in which, when the biological information measuring device 10 receives a measurement start instruction from the user via the input unit 27, the LFCT, which is an example of oxygen circulation time, is measured multiple times. The number of LFCT measurements is pre-stored in the non-volatile memory 24 of the biological information measuring device 10. The number of LFCT measurements stored in the non-volatile memory 24 can be changed by the user. The number of LFCT measurements performed by the biological information measuring device 10 in response to a single measurement start instruction needs to be two or more, and there is no restriction on the number of measurements. The number of LFCT measurements may also be specified by the user when issuing a measurement start instruction.

For ease of explanation, it is assumed that the number of LFCT measurements is set to "2" in the non-volatile memory 24 of the vital information measuring device 10. In other words, the vital information measuring device 10 will measure the LFCT twice in succession in response to a single measurement start instruction.

Furthermore, as explained using Figure 7, the time from when a subject who has stopped breathing resumes breathing until an inflection point in oxygen saturation appears varies for each subject. Therefore, the biological information measurement device 10 sets a reference time that specifies how long oxygen saturation measurement should continue after the subject resumes breathing. This reference time is called the "follow-up observation time T3."

The follow-up observation time T3 is set, for example, longer than the average LFCT so that LFCT can be measured even for subjects whose oxygen saturation inflection point appears later than other subjects. Specifically, the follow-up observation time T3 is determined in advance through experiments using an actual biological information measurement device 10. The follow-up observation time T3 is an example of the "oxygen circulation time measurement period" according to this embodiment.

In addition to the follow-up observation time T3, the non-volatile memory 24 of the vital information measuring device 10 also stores a predetermined breath-hold time T1 and a predetermined breath-adjustment time T2.

As an example, the following relationship exists between the breathing hold time T1, breathing adjustment time T2, and follow-up observation time T3:

Relationship 1: Breathing adjustment time T2 < follow-up observation time T3
Relationship 2: (breathing arrest time T1 + breathing adjustment time T2) > follow-up observation time T3

Figures 9 and 10 are flowcharts showing an example of the flow of the biometric information measurement process executed by the CPU 21 when a photoelectric sensor 11 is attached to the fingertip of the subject and an instruction to start measurement is received from the user via the input unit 27.

The biological information measurement program that defines the biological information measurement process is stored in advance, for example, in the ROM 22 of the biological information measurement device 10. The CPU 21 of the biological information measurement device 10 reads the biological information measurement program stored in the ROM 22 and executes the biological information measurement process.

When the biological information measurement device 10 receives an instruction to start measurement, it begins measuring oxygen saturation and stores the measured oxygen saturation in, for example, RAM 23.

Fig. 11 is a graph showing an example of time variation in the oxygen saturation level of the subject obtained by the biological information measurement process. The flow of the biological information measurement process will be described below with reference to the graph in Fig. 11. In the graph in Fig. 11, the biological information measurement device 10 receives an instruction to start measurement from the user via the input unit 27 at time _t0 .

First, in step S10 of Fig. 9, the CPU 21 notifies the subject to stop breathing as a preparatory action for the first LFCT measurement. In the graph of Fig. 11, the CPU 21 notifies the subject to stop breathing at time _t1 . That is, the first LFCT measurement starts at time _t1 .

In step S20, having notified the subject to stop breathing, the CPU 21 starts timer TM1. Timer TM1 is a timer for measuring the breathing stop time T1. The CPU 21 starts timer TM1, for example, using a timer function built into the CPU 21. If the CPU 21 does not have a built-in timer function, the CPU 21 may start timer TM1 using, for example, a timer unit (not shown) connected to the I/O 25.

In step S30, the CPU 21 determines whether the timer TM1 has reached the breathing stop time T1. If the timer TM1 has not reached the breathing stop time T1, the CPU 21 repeatedly executes the determination process of step S30 until the timer TM1 reaches the breathing stop time T1. Because the subject stops breathing until the timer TM1 reaches the breathing stop time T1, the subject's oxygen saturation level decreases after time _t1 , as shown in the graph of FIG. 11 .
Because there is a distance between the lungs and the fingertip, it takes time for the photoelectric sensor 11 attached to the fingertip to detect a decrease in oxygen saturation due to the subject's cessation of breathing. Therefore, after time _t1 , the oxygen saturation remains the same as before cessation of breathing, but then decreases towards time _t2 .

If it is determined in the determination process of step S30 in Figure 9 that the timer TM1 has reached the breathing arrest time T1, the process proceeds to step S40.

In step S40, the CPU 21 stops timer TM1. "Stopping" timer TM1 means halting the measurement of time by timer TM1 and setting the value of timer TM1 to "0." In other words, stopping timer TM1 is the same as resetting timer TM1.

In step S50, the CPU 21 notifies the subject to resume breathing. In the graph of Fig. 11, the CPU 21 notifies the subject to resume breathing at time _t2 , when breathing stop time T1 has elapsed since time _t1 . This causes the subject to resume breathing. In other words, the subject stops breathing for the entire breathing stop time T1.

As already explained, because there is a distance between the lungs and the fingertip, even if the subject resumes breathing at time _t2 , it takes time for the photoelectric sensor 11 attached to the fingertip to detect the increase in oxygen saturation due to the subject's resumption of breathing. Therefore, the oxygen saturation continues to decrease even after time _t2 has passed.

When the subject resumes breathing, the CPU 21 starts the first monitoring of oxygen saturation in step S60. "Starting monitoring of oxygen saturation" refers to a state in which the CPU 21 associates the time when the subject resumes breathing (time _t2 in this case) with the oxygen saturation measured at time _t2 when the subject resumes breathing, and then detects a change in the oxygen saturation used for measuring the LFCT.

Therefore, in step S70, the CPU 21 activates timers TM2 and TM3. Timer TM2 is a timer for measuring a breathing adjustment time T2. Timer TM3 is a timer for measuring a follow-up observation time T3. That is, the CPU 21 continues measuring oxygen saturation from time _t2 until the follow-up observation time T3 has elapsed.

Meanwhile, the subject who has resumed breathing will regulate their breathing in preparation for the second LFCT measurement.

In step S80, the CPU 21 determines whether the timer TM2 started in step S70 has reached the breathing adjustment time T2. If the timer TM2 has not reached the breathing adjustment time T2, the CPU 21 repeatedly executes the determination process of step S80 until the timer TM2 reaches the breathing adjustment time T2.

If it is determined in the determination process of step S80 that the timer TM2 has reached the breathing adjustment time T2, the process proceeds to step S90, where the CPU 21 stops the timer TM2.

In step S100, the CPU 21 notifies the subject to stop breathing as a preparatory action for the second LFCT measurement. In the graph of Fig. 11, the CPU 21 notifies the subject to stop breathing at time _t3 . That is, the second LFCT measurement starts at time _t3 .

After instructing the subject to stop breathing, in step S110, the CPU 21 starts timer TM1.

As already explained, due to the relationship "breathing adjustment time T2 < follow-up observation time T3," the first LFCT measurement continues even after time _t3 . That is, the CPU 21 redundantly performs the first LFCT measurement even after time _t3 , when the subject stops breathing to perform the second LFCT measurement. Therefore, even if the second LFCT measurement is started, it is possible to measure the LFCT of the subject such that the inflection point of oxygen saturation appears after the breathing adjustment time T2 has elapsed.

In step S120, the CPU 21 determines whether the timer TM3 started in step S70 has reached the elapsed observation time T3. If the timer TM3 has not reached the elapsed observation time T3, the CPU 21 proceeds to step S160 to continue the first LFCT measurement.

In step S160, the CPU 21 determines whether the timer TM1 started in step S110 has reached the respiratory arrest time T1. If the timer TM1 has not reached the respiratory arrest time T1, the process proceeds to step S120. That is, the CPU 21 alternately executes the determination process of step S120 and the determination process of step S160 until the timer TM3 has reached the follow-up observation time T3.

If it is determined in the determination process of step S120 that the timer TM3 has reached the elapsed observation time T3, the process proceeds to step S130. In the graph of Fig. 11, the timer TM3 has reached the elapsed observation time T3 at time _t4 .

When the first oxygen saturation observation ends at time _t4 , the first LFCT measurement also ends. Therefore, in step S130, the CPU 21 stops the timer TM3.

In step S140, the CPU 21 retrieves the oxygen saturation measured over the follow-up observation time T3 in chronological order from the RAM 23, detects the inflection point of the oxygen saturation, and then measures the time from the time _t2 when the subject resumes breathing to the time when the inflection point of the oxygen saturation is indicated, and sets this as the first LFCT measurement result.

In step S150, the CPU 21 notifies the user of the first LFCT measurement result measured in step S140, for example, by displaying it on the display unit 28. The CPU 21 then proceeds to step S160 and determines whether the timer TM1 has reached the breathing arrest time T1.

If the determination process in step S160 determines that timer TM1 has reached breathing arrest time T1, the process proceeds to step S170 in Figure 10.

Since measurement of the breathing hold time T1 has ended, in step S170, the CPU 21 stops the timer TM1.

In step S180, the CPU 21 notifies the subject to resume breathing. In the graph of Fig. 11, the CPU 21 notifies the subject to resume breathing at time _t5 , when the breathing stop time T1 has elapsed since time _t3 . This causes the subject to resume breathing.

As the subject resumes breathing, in step S190, the CPU 21 begins a second oxygen saturation monitoring. Therefore, in step S200, the CPU 21 activates timer TM3. Note that in the first oxygen saturation monitoring, in step S70 of FIG. 9, the CPU 21 activated timer TM2 in addition to timer TM3. However, since the second oxygen saturation monitoring is the final oxygen saturation monitoring, the subject does not need to regulate their breathing in preparation for the next LFCT measurement. Therefore, the CPU 21 does not need to activate timer TM2.

In step S210, the CPU 21 determines whether the timer TM3 started in step S200 has reached the elapsed observation time T3. If the timer TM3 has not reached the elapsed observation time T3, the CPU 21 repeatedly executes the determination process of step S210.

On the other hand, if it is determined in the determination process of step S210 that the timer TM3 has reached the elapsed observation time T3, the process proceeds to step S220. In the graph of Fig. 11, the timer TM3 has reached the elapsed observation time T3 at time _t6 .

When the second oxygen saturation observation ends at time _t6 , the second LFCT measurement also ends. Therefore, in step S220, the CPU 21 stops the timer TM3.

In step S230, the CPU 21 retrieves from the RAM 23 the oxygen saturation measured over the follow-up observation time T3 from time _t5 to time _t6 in chronological order, and detects the inflection point of the oxygen saturation. The CPU 21 then measures the time from time _t5 , when the subject resumes breathing, to the time when the inflection point of the oxygen saturation appears, and sets this as the second LFCT measurement result.

In step S240, the CPU 21 notifies the user of the second LFCT measurement result measured in step S230, for example, by displaying it on the display unit 28.

In step S250, the CPU 21 substitutes the first LFCT obtained in step S140 and the second LFCT measured in step S230 into a predetermined equation that represents the relationship between LFCT and cardiac output, for example, to measure the cardiac output for each measurement.

Note that even if the CPU 21 measures the subject's LFCT, it is not necessary to also measure the subject's cardiac output. Therefore, the CPU 21 does not need to execute the process of step S250.

The CPU 21 then terminates the biological information measurement process shown in Figures 9 and 10.

In this way, when the biological information measurement device 10 measures the subject's LFCT multiple times in response to a single measurement start instruction, it notifies the subject to stop breathing before the oxygen saturation follow-up observation time T3 from the previous measurement ends in order to prepare for the next LFCT measurement.

On the other hand, Figure 12 is a graph showing an example of the change in the oxygen saturation level of a subject over time when, after the oxygen saturation observation time T3 in the first LFCT measurement has ended, the subject is notified to stop breathing in preparation for the second LFCT measurement.

In the graph shown in Figure 12, the first follow-up observation time T3 from time _t2 to time _t3 and the second breath-hold time T1 from time _t3 to time _t5 do not overlap. Therefore, the time _t6 corresponding to the end of the second LFCT measurement shown in Figure ₁₂ is longer than the time t6 corresponding to the end of the second LFCT measurement shown in Figure 11 by the time ( _t4 - _t3 ) in Figure 11. In other words, the biological information measurement device 10 according to this embodiment can shorten the time required to measure LFCT multiple times compared to starting the next LFCT measurement after the previous LFCT measurement has ended. Furthermore, as the time required to measure LFCT is shortened, the time required to measure biological information calculated from LFCT, such as cardiac output, is also shortened.

In the biological information measurement process shown in Figures 9 and 10, an example has been described in which LFCT is notified for each LFCT measurement. However, after a specified number of LFCT measurements have been completed, the LFCT measured in each measurement may be notified together. Specifically, rather than notifying the LFCT for the first measurement in step S150 of Figure 9, the LFCT for the first measurement and the LFCT for the second measurement may be notified together in step S240 of Figure 10.

Furthermore, the biological information measurement device 10 does not need to measure LFCT for each LFCT measurement. Specifically, the biological information measurement device 10 stores only the chronological changes in oxygen saturation in the non-volatile memory 24 without executing steps S140, S150, S230, S240, and S250 of the biological information measurement process shown in FIGS. 9 and 10 . Then, after the biological information measurement process is completed, the biological information measurement device 10 retrieves the oxygen saturation from the non-volatile memory 24 in response to a user instruction and measures the LFCT for each measurement. By storing the oxygen saturation after the start of measurement in chronological order in the non-volatile memory 24, the biological information measurement device 10 can retrieve the measured oxygen saturation at any time later, thereby measuring the LFCT for each measurement at the timing instructed by the user. This LFCT measurement method is applicable, for example, to a situation in which a subject measures their oxygen saturation at home, and a medical professional later checks the subject's oxygen saturation and LFCT at a hospital.

Second Embodiment
In the first embodiment, the follow-up observation time T3 is a fixed value. However, in order to measure the LFCT of the subject, the oxygen saturation may be measured from the time the subject resumes breathing until an inflection point in the oxygen saturation is detected.

Therefore, in the second embodiment, we will describe a biological information measurement device 10 that performs control to vary the follow-up observation time T3 depending on the detection status of the oxygen saturation inflection point in the final LFCT measurement.

Figure 13 is a flowchart showing an example of the flow of the biological information measurement process executed by the CPU 21 following the biological information measurement process according to the first embodiment shown in Figure 9.

When the biological information measurement device 10 receives an instruction to start measurement, it begins measuring oxygen saturation and stores the measured oxygen saturation in, for example, RAM 23.

Note that, like the biological information measurement device 10 according to the first embodiment, the biological information measurement device 10 according to the second embodiment also performs two consecutive LFCT measurements in response to a single measurement start instruction.

In step S160 of the biological information measurement process shown in Figure 9, if it is determined that timer TM1, which was started when the subject stopped breathing for the second time, has reached breathing cessation time T1, the process proceeds to step S300 in Figure 13.

Now that the second measurement of the breathing hold time T1 has been completed, in step S300, the CPU 21 stops the timer TM1.

In step S310, the CPU 21 notifies the subject to resume breathing. This causes the subject to resume breathing.

When the subject resumes breathing, in step S320, the CPU 21 begins monitoring the oxygen saturation level during the second, or final, LFCT measurement.

In step S330, the CPU 21 acquires changes in oxygen saturation during follow-up and determines whether an inflection point in the subject's oxygen saturation has been detected. If an inflection point in oxygen saturation has not been detected, the determination process of step S330 is repeated until an inflection point in oxygen saturation is detected. On the other hand, if an inflection point in oxygen saturation has been detected, the process proceeds to step S340.

In step S340, the CPU 21 measures the time from time _t5 when the subject resumes breathing to time _t60 when an inflection point of oxygen saturation appears, and sets this as the second LFCT measurement result.

In step S350, the CPU 21 notifies the user of the second LFCT measurement result measured in step S340, for example, by displaying it on the display unit 28.

In step S360, the CPU 21 substitutes the first LFCT obtained in step S140 of FIG. 9 and the second LFCT measured in step S340 into a predetermined equation that represents the relationship between LFCT and cardiac output, for example, to measure the cardiac output for each measurement.

The CPU 21 then ends the biological information measurement process according to the second embodiment shown in Figures 9 and 13.

In other words, the CPU 21 of the biological information measurement device 10 according to the second embodiment performs control so that the period from when the subject resumes breathing until an inflection point in oxygen saturation is detected during the final LFCT measurement is the follow-up observation time T3.

FIG. 14 is a graph showing an example of the change in the oxygen saturation of a subject over time when, in the final LFCT measurement, the inflection point of the subject's oxygen saturation is detected from the time _t5 when the subject resumes breathing until the predetermined follow-up observation time T3, i.e., before the pre-change follow-up observation time T3, has elapsed.

As shown in Figure 14, if the time _t60 at which an inflection point in oxygen saturation appears is before time t6, which is the time from time _t5 to the original follow-up observation time _T3 , the follow-up observation time T3 is shortened to the period from time _t5 to time _t60 . In the example shown in Figure 14, the shortened follow-up observation time T3 is indicated by hatching.

In other words, the biological information measuring device 10 according to the second embodiment can shorten the time required from receiving an instruction to start measurement from the user to completing the final LFCT measurement, compared to when the second LFCT measurement is completed after the pre-change predetermined follow-up observation time T3 has elapsed.

On the other hand, Figure 15 is a graph showing an example of the change in the oxygen saturation level of the subject over time when, in the second LFCT measurement, the inflection point of the subject's oxygen saturation level is detected after the elapse of the pre-change follow-up observation time T3 from the time _t5 when the subject resumed breathing.

As shown in Figure 15, if the time _t60 at which an inflection point in oxygen saturation appears is after time t6, which is the time from time _t5 to the original follow-up observation time _T3 , the follow-up observation time T3 is extended to the period from time _t5 to time _t60 . In the example shown in Figure 15, the extended follow-up observation time T3 is indicated by hatching.

If breathing is repeatedly stopped, the oxygen saturation inflection point may appear later in the later LFCT measurements than in the earlier LFCT measurements.

In other words, the biological information measurement device 10 according to the second embodiment does not have to abort the LFCT measurement midway through, even if the oxygen saturation inflection point appears after the elapse of the pre-change follow-up observation time T3 during the final LFCT measurement. Therefore, the LFCT of the subject can be measured more accurately than when the length of the follow-up observation time T3 is not adjusted.

In the second embodiment, a control example was described in which the period from when the subject resumes breathing until an inflection point in oxygen saturation is detected in the final LFCT measurement is set as the follow-up observation time T3. The CPU 21 of the biological information measurement device 10 may also apply this control of varying the follow-up observation time T3 in accordance with the detection of an inflection point in oxygen saturation to other LFCT measurements other than the final LFCT measurement. In this case, the user may set a measurement in which the follow-up observation time T3 is varied in accordance with the detection of an inflection point in oxygen saturation.

<Modification>
Various modifications of the first and second embodiments will be described.

The CPU 21 of the biological information measuring device 10 may vary the breathing adjustment time T2 depending on the measurement status of the subject's LFCT, rather than setting the breathing adjustment time T2 to a fixed value.

For example, if a subject repeatedly stops breathing, even if the duration of each breath stop is the same, the longer the breath stop, the more difficult it tends to be. Therefore, the CPU 21 may perform control to adjust the breathing adjustment time T2 so that it becomes longer as the LFCT measurement for the same subject approaches the final measurement.

As the subject's breathing becomes more difficult, the oxygen saturation at the end of the fixed breathing adjustment time T2, i.e., the oxygen saturation before breathing stops, may decrease. Therefore, for each LFCT measurement, the CPU 21 may set the extension rate of the breathing adjustment time T2 using the rate of decrease in oxygen saturation before breathing stops in the immediately preceding LFCT measurement. For example, the CPU 21 may use the rate of decrease in oxygen saturation before breathing stops in the immediately preceding LFCT measurement as the extension rate of the breathing adjustment time T2 for the next LFCT measurement.

Note that the CPU 21 does not need to make the breathing adjustment time T2 for each LFCT measurement longer than the breathing adjustment time T2 for the immediately preceding LFCT measurement. For example, the breathing adjustment time T2 for each measurement up to a predetermined intermediate LFCT measurement (referred to as an "intermediate measurement") may be the same, and the breathing adjustment time T2 for each LFCT measurement after the intermediate measurement may be longer than the breathing adjustment time T2 for each LFCT measurement before the intermediate measurement.

In addition, rather than setting the breath-hold time T1 to a fixed value, the CPU 21 may vary the breath-hold time T1 depending on the measurement conditions of the subject's LFCT.

As already explained, subjects tend to find it more difficult to hold their breath as the final LFCT measurement approaches. In response to this, the length of the breathing adjustment time T2 was adjusted in the above example, but the CPU 21 may also perform control to adjust the breathing hold time T1 so that it is shorter as the LFCT measurement for the same subject approaches the final measurement.

In this case, the CPU 21 may set the shortening rate of the breathing hold time T1 for each LFCT measurement using the rate of decrease in oxygen saturation during normal times in the immediately preceding LFCT measurement. For example, the CPU 21 may use the rate of decrease in oxygen saturation before breathing hold in the immediately preceding LFCT measurement as the shortening rate of the breathing hold time T1 in the next LFCT measurement.

As mentioned above, there are individual differences in the time it takes for an oxygen saturation inflection point to appear after a subject resumes breathing. The oxygen saturation value at the inflection point also varies from person to person, resulting in variability. Therefore, the breathing hold time T1 is set to a length that will cause the oxygen saturation value at the inflection point to fall below the oxygen saturation reference value H for as many subjects as possible.

However, there are some subjects whose oxygen saturation inflection point does not fall below the oxygen saturation reference value H, for example, due to changes in their physical condition. The accuracy of the LFCT measured for such subjects may be lower than the accuracy of the LFCT measured when the oxygen saturation inflection point falls below the oxygen saturation reference value H.

On the other hand, there are some subjects whose oxygen saturation inflection point value is lower than the oxygen saturation reference value H by a significant amount. The accuracy of the LFCT measured on such subjects may not be different from the accuracy of the LFCT measured when the oxygen saturation inflection point value is the same as the oxygen saturation reference value H.

The value at the oxygen saturation inflection point varies depending on the length of the breathing pause time. Therefore, the CPU 21 may perform control to vary the breathing pause time T1 according to the difference between the subject's minimum oxygen saturation value, i.e., the value at the oxygen saturation inflection point, and the oxygen saturation reference value H.

Figure 16 is a diagram showing an example of the difference between the value at an oxygen saturation inflection point and the oxygen saturation reference value H. Oxygen saturation curve 30 in Figure 16 shows an example in which the value at the oxygen saturation inflection point is not below the oxygen saturation reference value H, while oxygen saturation curve 32 shows an example in which the value at the oxygen saturation inflection point is below the oxygen saturation reference value H. Furthermore, difference e1 represents the difference between the inflection point on oxygen saturation curve 30 and the oxygen saturation reference value H, and difference e2 represents the difference between the inflection point on oxygen saturation curve 32 and the oxygen saturation reference value H.

For a subject whose oxygen saturation value at the inflection point does not fall below the oxygen saturation reference value H, as in the oxygen saturation curve 30, the CPU 21 lengthens the breath-hold time T1 from the preset breath-hold time T1 as the difference between the oxygen saturation value at the inflection point and the oxygen saturation reference value H increases, so that the oxygen saturation inflection point falls below the oxygen saturation reference value H. By lengthening the breath-hold time T1 from the preset breath-hold time T1, the accuracy of the LFCT measurement is improved compared to before the breath-hold time T1 was extended.

Furthermore, for a subject whose oxygen saturation value at the inflection point is lower than the oxygen saturation reference value H by an unnecessarily large amount, as in the oxygen saturation curve 32, the CPU 21 shortens the breath-hold time T1 from the preset breath-hold time T1 so that the oxygen saturation inflection point falls below the oxygen saturation reference value H and approaches the oxygen saturation reference value H as the difference between the oxygen saturation value at the inflection point and the oxygen saturation reference value H increases. By shortening the breath-hold time T1 from the preset breath-hold time T1, the time required to measure the LFCT is reduced compared to before the breath-hold time T1 was shortened, while maintaining the accuracy of the LFCT measurement.

The above describes one aspect of the biological information measuring device 10 using an embodiment, but the disclosed form of the biological information measuring device 10 is just one example, and the form of the biological information measuring device 10 is not limited to the scope described in the embodiment. Various modifications or improvements can be made to the embodiment without departing from the gist of this disclosure, and forms incorporating such modifications or improvements are also included in the technical scope of the disclosure. For example, the order of the biological information measurement process shown in the first and second embodiments may be changed without departing from the gist of this disclosure.

Furthermore, in the above embodiment, an example has been described in which the biological information measurement process is implemented by software. However, processing equivalent to the biological information measurement process shown in Figures 9 and 10, and Figures 9 and 13, may also be performed by hardware. In this case, processing can be performed faster than when the biological information measurement process is implemented by software.

In the above embodiment, the term "processor" refers to a processor in a broad sense, including general-purpose processors (e.g., CPU 21) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

Furthermore, the processor operations in the above embodiments may not only be performed by a single processor, but may also be performed by multiple processors located in physically separate locations working together. Furthermore, the order of the processor operations is not limited to the order described in the above embodiments, and may be changed as appropriate.

In the above embodiment, an example was described in which the biological information measurement program is stored in ROM 22, but the storage location of the biological information measurement program is not limited to ROM 22. The biological information measurement program of the present disclosure can also be provided in a form recorded on a storage medium readable by computer 20. For example, the biological information measurement program may be provided in a form recorded on an optical disc such as a CD-ROM (Compact Disk Read Only Memory) or a DVD-ROM (Digital Versatile Disk Read Only Memory). The biological information measurement program may also be provided in a form recorded on a portable semiconductor memory such as a USB (Universal Serial Bus) memory or a memory card.

ROM 22, non-volatile memory 24, CD-ROM, DVD-ROM, USB, and memory cards are examples of non-transitory storage media.

Furthermore, the biological information measurement device 10 may download a biological information measurement program from an external device connected to the communication unit 29 via a communication line and store the downloaded biological information measurement program in a non-transitory storage medium. In this case, the CPU 21 of the biological information measurement device 10 reads the biological information measurement program downloaded from the external device from the non-transitory storage medium and executes the biological information measurement process.

1, 1A, 1B Light-emitting element 3 Light-receiving element 4 Artery 5 Vein 6 Capillary 8 Living body 10 Biological information measuring device 11 Photoelectric sensor 12 Pulse wave processing unit 13 Oxygen saturation measuring unit 14 Oxygen circulation time measuring unit 15 Cardiac output measuring unit 16 Timer unit 17 Notification unit 20 Computer 21 CPU
22 ROM
23 RAM
24 Non-volatile memory 25 I/O
26 Bus 27 Input unit 28 Display unit 29 Communication units 30, 32 Oxygen saturation curve 94 Arrows 96, 97 Light absorption curve 98 Red area 99 Infrared area H Reference value S Oxygen saturation T1 Breathing stop time T2 Breathing adjustment time T3 Follow-up observation times TM1, TM2, TM3 Timers e1, e2 Difference

Claims (9)

a processor;
The processor:
A biological information measuring device that, when measuring the oxygen circulation time, which is the time required for oxygen to circulate through the arteries, veins, and capillaries that are distributed throughout the body of a person being measured, and which is the time from when the person resumes breathing after having stopped it until an inflection point at which the oxygen saturation in the person's blood changes from decreasing to increasing is detected , continuously multiple times , notifies the person being measured to stop breathing if the elapsed time since the person being measured resumed breathing reaches a breathing adjustment time, which is the time from when the person is instructed to resume breathing until when the person is again instructed to stop breathing, as a preparatory action for measuring the oxygen circulation time in the next measurement, and which is set to a time shorter than the measurement period of the oxygen circulation time of the person being measured, before reaching a measurement period of the oxygen circulation time that is set to a predetermined length as a period for observing the oxygen saturation in the person 's blood. The biological information measurement device according to claim 1 , wherein the processor varies the respiration adjustment time in accordance with a measurement status of an oxygen circulation time of the measurement subject. The biological information measurement device according to claim 2 , wherein the processor controls the breathing adjustment time so that the breathing adjustment time becomes longer as the measurement of the oxygen circulation time of the subject approaches the final measurement. The biological information measuring device according to claim 2 , wherein the processor performs control to set the breathing adjustment time to the period from when the subject, who has stopped breathing, is instructed to resume breathing until when the inflection point is detected. The biological information measuring device according to claim 4 , wherein the processor controls the measurement of the oxygen circulation time so as not to end until the inflection point is detected in the final measurement of the oxygen circulation time for the subject. The processor controls the breathing hold time, which is the period from when the subject is instructed to stop breathing to when the subject is instructed to resume breathing, so as the measurement of the subject's oxygen circulation time approaches the final measurement. A biological information measuring device as described in any one of claims 1 to 5. The processor varies the breathing stop time, which is the period from when the subject is instructed to stop breathing to when the subject is instructed to resume breathing, depending on the difference between the lowest oxygen saturation value in the subject's blood and a predetermined oxygen saturation reference value that specifies the lowest oxygen saturation value required for measuring oxygen circulation time. A biological information measuring device as described in any one of claims 1 to 5. The biological information measuring device according to claim 7 , wherein the processor shortens the breath-hold time as the difference increases when the minimum value is equal to or less than the reference value, and lengthens the breath-hold time as the difference increases when the minimum value exceeds the reference value. A biological information measurement program for causing a computer to execute a process of notifying the subject to stop breathing when the elapsed time since the subject resumed breathing reaches a breathing adjustment time, which is the time from when the subject is instructed to resume breathing to when the subject is again instructed to stop breathing, as a preparatory action for measuring the oxygen circulation time in the next measurement, before reaching a measurement period for the oxygen circulation time set to a predetermined length as a period for observing the subject's blood oxygen saturation, in the case where the measurement of the oxygen circulation time is performed multiple times in succession, the program notifying the subject to stop breathing when the elapsed time since the subject resumed breathing reaches a breathing adjustment time, which is the time from when the subject is instructed to resume breathing to when the subject is again instructed to stop breathing, as a preparatory action for measuring the oxygen circulation time in the next measurement, before reaching a measurement period for the oxygen circulation time set to a predetermined length as a period for observing the subject's blood oxygen saturation.