Blood volume measuring method, blood volume measuring device, and program

Abstract

To provide a blood volume measuring method, a blood volume measuring device, and a program that allow calibration to be performed at an appropriate timing.SOLUTION: A blood volume measuring method for calculating cardiac output includes: a first measurement step of measuring a first value in a prescribed section of a first biological information parameter including at least one of a pulse wave propagation time and pulse pressure of a subject; a second measurement step of measuring a second value in a section longer than a prescribed section of a second biological information parameter including at least one of the pulse wave propagation time, a cardiac rate, and pulse pressure of the subject; a base line determination step of determining whether or not the difference between the first value and the second value is a threshold or less; a calibration step of calculating a coefficient unique to the subject on the basis of the second value when the difference between the first value and the second value is determined to be a threshold or less in the base line determination step; and a calculation step of calculating cardiac output on the basis of the first value and the coefficient unique to the subject calculated in the calibration step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a blood volume measurement method, a blood volume measurement device, and a program. [Background technology]

[0002] In medical facilities, it is necessary to monitor as continuously as possible the hemodynamic changes of subjects in operating rooms, intensive care units, emergency rooms, dialysis rooms, etc. Conventionally, such monitoring of hemodynamic changes of subjects has been mainly performed by directly monitoring blood pressure.

[0003] However, the living body regulates cardiac output and vascular resistance so that central blood pressure falls within a certain range. Therefore, direct blood pressure monitoring alone is not sufficient to know early changes in the subject's circulatory dynamics, and when a change in blood pressure is observed, it is necessary to know the cause. For this reason, in addition to monitoring blood pressure, cardiac output must be monitored. Methods for measuring cardiac output include thermodilution, dye dilution, and ultrasound.

[0004] However, all of the above-mentioned methods require advanced skills from medical professionals and are highly invasive to the subject, so they cannot be easily and continuously performed, making it difficult to use these methods to continuously monitor changes in the subject's circulatory dynamics at all times.

[0005] In response to this, the following Patent Document 1 discloses a method for measuring blood volume that can continuously and non-invasively monitor the circulatory dynamics of a subject, does not require the skills of a skilled medical professional, such as catheter insertion, and causes little pain to the subject. According to this blood volume measurement method, cardiac output is calculated by utilizing the correlation between pulse wave transit time and stroke volume. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4742644 Summary of the Invention [Problem to be solved by the invention]

[0007] In the blood volume measurement method disclosed in Patent Document 1, cardiac output is calculated from pulse wave transit time PWTT, pulse pressure PP, heart rate HR, and subject-specific coefficients α, β, and K. To obtain the coefficients α, β, and K (hereinafter also referred to as calibration), it is necessary to measure a plurality of calibration parameters including the pulse wave transit time PWTT, heart rate HR, and pulse pressure PP.

[0008] Instantaneous values ​​are used for the pulse wave transit time PWTT, pulse pressure PP, and heart rate HR used to calculate cardiac output. On the other hand, moving average values ​​over a certain period of time are used for the pulse wave transit time PWTT, heart rate HR, and pulse pressure PP used as calibration parameters, rather than instantaneous values, to reduce the influence of momentary noise such as sudden movements of the subject. Therefore, if calibration is performed at a time when the subject's circulatory dynamics are changing, the instantaneous value and the moving average value may deviate significantly, causing a large change in the calculated cardiac output before and after calibration.

[0009] Therefore, an object of the present disclosure is to provide a blood volume measurement method, a blood volume measurement device, and a program that can perform calibration at an appropriate timing. [Means for solving the problem]

[0010] A method for measuring blood volume according to one aspect of the present disclosure includes: A method for calculating cardiac output from a biological information parameter of a subject, comprising: a first measuring step of measuring a first value in a predetermined section of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject; a second measuring step of measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination step of determining whether a difference between the measured first value and the measured second value is equal to or less than a threshold value; a calibration step of calculating a coefficient specific to the subject based on the second value when the difference between the first value and the second value is determined to be equal to or less than the threshold value in the baseline determination step; A calculation step of calculating the cardiac output based on the first value and a coefficient specific to the subject calculated in the calibration step.

[0011] A blood volume measurement device according to one aspect of the present disclosure includes: A measurement device for calculating cardiac output from a biological information parameter of a subject, a first measurement means for measuring a first value of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject in a predetermined section; A second measuring means for measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination means for determining whether a difference between the measured first value and the measured second value is equal to or smaller than a threshold value; a calibration means for calculating a coefficient specific to the subject based on the second value when the baseline determination means determines that the difference between the first value and the second value is equal to or smaller than the threshold value; A calculation means calculates the cardiac output based on the first value and a coefficient specific to the subject calculated by the calibration means.

[0012] A program according to one aspect of the present disclosure includes: On the computer, a first measuring step of measuring a first value of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject in a predetermined section; a second measuring step of measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination step of determining whether a difference between the measured first value and the measured second value is equal to or less than a threshold value; a calibration step of calculating a coefficient specific to the subject based on the second value when the difference between the first value and the second value is determined to be equal to or less than the threshold value in the baseline determination step; A calculation step of calculating a cardiac output based on the first value and the subject-specific coefficient calculated in the calibration step is executed. Effect of the Invention

[0013] According to the present disclosure, it is possible to reduce the influence of momentary noise and prevent a large variation in the calculated value of cardiac output before and after calibration, thereby enabling accurate calculation of the cardiac output of the subject. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a configuration of one embodiment of a biological information monitor including a blood content measuring device according to the present disclosure. [Diagram 2] FIG. 2 is a diagram showing an example of a measurement form in which an electrocardiogram measuring means and a peripheral pulse wave detecting means are attached to a subject. [Diagram 3] 1 is a flowchart showing the procedure for calibrating α, β, and K to calculate esCCO. [Figure 4] FIG. 1 is a diagram showing the relationship between PEP, PWTTa, PWTTb, and PWTT. [Diagram 5] 11 is a graph showing the relationship between the instantaneous value and the moving average value of a calibration parameter. [Figure 6] 11 is a graph showing the relationship between a threshold value and the elapsed time from the start of moving average measurement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an embodiment of a blood volume measurement method and a blood volume measurement device according to the present disclosure will be described with reference to the accompanying drawings.

[0016] First, the principle of measuring the amount of blood ejected by the beating of the heart (Cardiac Output, CO) will be described below. Using the Windkessel model, a diagnostic index for blood vessels, the flow rate of blood flowing into the aorta during cardiac systole, that is, the stroke volume (SV: Stroke Volume) minus the flow rate (Qs) flowing out to the periphery during systole, can be expressed as follows using the aortic compliance (C) and pulse pressure (PP: Pulse Pressure, the difference between the systolic blood pressure (maximum blood pressure) value and the diastolic blood pressure (minimum blood pressure) value): SV-Qs=C*PP (Formula 1)

[0017] The flow rate (Qd) flowing out to the periphery during the diastole of the heart is equal to the above SV-Qs. Qs and Qd are calculated by dividing the systolic and diastolic arterial pressure (V) by the vascular resistance (R) and multiplying it by the systolic time Ts and the diastolic time Td, respectively. If we consider them to be proportional to Ts and Td, respectively, they can be expressed as follows: (Qd = )SV-Qs=SV*Td / (Ts+Td) (Equation 2)

[0018] From Equation 1 and Equation 2 SV*Td / (Ts+Td)=C*PP SV=C*PP*(1+Ts / Td) (Equation 3)

[0019] Here, assuming that C and Ts / Td are constant during the measurement period and C*(1+Ts / Td)=K, it can be expressed as follows. SV=K*PP (formula 4) PP=SV*1 / K (Formula 5) Thus, according to the Windkessel model, pulse pressure PP is proportional to stroke volume SV.

[0020] The pulse pressure PP1 actually measured consists of the pulse pressure PP2 based on Equation 5 (although Equation 5 uses PP, in the following explanation it will be referred to as PP2) and the increased pulse pressure PP3 seen when using a vasoconstrictor, etc., and can be expressed as follows: PP1=PP2+PP3 (Formula 6)

[0021] If PP3 does not exist, from Equation 4 and Equation 6, SV=K*PP1 (Formula 7) Thus, SV can be calculated from the measured blood pressure (pulse pressure PP1). However, when using vasoconstrictors, PP1 includes PP3, which causes SV to be overestimated. This has been a problem when calculating SV from blood pressure.

[0022] As mentioned above, regarding the measurement accuracy of the device that calculates stroke volume and cardiac output from the invasively measured arterial blood pressure waveform, it has been reported that "in a subject who was admitted to the ICU (intensive care unit) after surgery, when the vascular resistance changed by about 60% due to the administration of the vasoconstrictor phenylephrine, the measurement value of the device mentioned above showed a significantly higher bias than the measurement value of the thermodilution cardiac output meter used as the standard, so in such cases it is necessary to recalibrate with a thermodilution cardiac output meter." It is known that when a vasoconstrictor is used, the pulse pressure increases due to the influence of reflected waves from the peripheral side, and PP3 corresponds to this.

[0023] The pulse wave transit time (PWTT), which is the time it takes for the R wave of the electrocardiogram to reach the peripheral SpO2 pulse wave, can be expressed as follows: PWTT=PEP+PWTTa+PWTTb (Formula 8)

[0024] FIG. 4 is a diagram showing the waveforms of each pulse wave measured from a subject. As shown in the figure, PEP is the pre-ejection time of the heart, which is the time from when the heart starts to be electrically excited to when the aortic valve opens. In addition, PWTTa is the time from when the aortic valve opens and a pulse wave is generated in the aorta to when it propagates to the peripheral artery where blood pressure measurement is usually performed invasively. In addition, PWTTb is the time until the pulse wave propagates from the peripheral artery to the blood vessel where the peripheral photoelectric pulse wave is measured.

[0025] Ten adult dogs were used to measure the time from the R wave of the electrocardiogram (ECG) to the onset of the femoral artery pulse wave (PEP+PWTTa).The relationship between the time of PEP+PWTTa and blood pressure was measured under the following conditions: administration of a vasoconstrictor, administration of a vasodilator, enhancement of cardiac contractility, reduction of cardiac contractility, and blood removal.A correlation was found between pulse pressure PP1 and the time of PEP+PWTTa.

[0026] The relationship between pulse pressure PP1 and PEP+PWTTa can be expressed as follows. PEP+PWTTa=a*PP1+b (Equation 9) Moreover, the relationship between PWTTb and PP1 is expressed as follows: PWTTb=c*PP1+d+e (Equation 10)

[0027] It was found that when PP3 appears due to the use of a vasoconstrictor, etc., PWTTb tends to be prolonged compared to under other conditions, and the amount of prolongation corresponding to this was designated as e (here, e is not necessarily a constant).

[0028] Therefore, by rewriting Equation 8 into Equation 9 and Equation 10, it can be expressed as follows. PWTT = (a*PP1+b) + (c*PP1+d+e) PP1=1 / (a+c)*(PWTT-bde) (Equation 11)

[0029] Substituting the right side of equation 5 into PP2 in equation 6 gives the following: PP1=SV*1 / K+PP3 (Formula 12) From equations 11 and 12, the following can be expressed: 1 / (a+c)*PWTT-(b+d) / (a+c)=SV*1 / K+PP3+e / (a+c) SV=K*(1 / (a+c)*PWTT-(b+d) / (a+c))-K*(PP3+e / (a+c)) (Equation 13)

[0030] As mentioned above, we experimentally found that when PP3 appears due to the use of vasoconstrictors, PWTTb tends to be prolonged. When phenylephrine is administered, PP3 appears and PP1 increases. However, the relationship between PWTTb and PP1, as seen during blood loss or pentobarbital administration, is no longer seen when phenylephrine is administered, and PWTTb tends to be prolonged. Therefore, we experimentally found that the negative correlation between SV and PWTT is maintained even when phenylephrine is administered, similar to that under other conditions, and therefore the second term on the right side of Equation 13, "K*(PP3+e / (a+c))," can be almost ignored.

[0031] Therefore, if we set 1 / (a+c)=α and -(b+d) / (a+c)=β, we can express it as follows. SV=K*(α*PWTT+β) (Equation 14) α and β are values ​​that are calibrated and calculated using parameters obtained from the subject, such as PWTT, and are coefficients unique to the subject.

[0032] Furthermore, based on the relationship SV = CO / HR, the estimated continuous cardiac output (esCCO) can be calculated as follows (HR: Heart Rate): esCCO=K*(α*PWTT+β)*HR (Equation 15) where esCCO is cardiac output in L / min and K is a subject-specific constant.

[0033] Incidentally, Equation 15 can also be replaced as follows: esCCO=(αK*PWTT+βK)*HR (Equation 16) αK and βK are coefficients specific to the subject.

[0034] When SV and esCCO are calculated using PWTT as in Equations 14, 15, and 16, the relationship between SV and PWTT is maintained similar to that under other conditions even when pulse pressure is increased by using a vasoconstrictor, thus resolving the problems seen when SV is calculated using conventional blood pressure. Therefore, CO is not overestimated.

[0035] Next, one embodiment of a biological information monitor equipped with a blood content measuring device according to the present disclosure will be described with reference to Fig. 1. In the description, Fig. 2 showing an example of a measurement form by the biological information monitor will be referred to as appropriate.

[0036] The vital sign monitor M comprises a blood volume measuring device 1 for measuring the subject's blood volume, a non-invasive blood pressure measuring device 2 for measuring the blood pressure during systole and diastole, a pulse wave transit time detecting device 3 for detecting electrocardiogram R waves and peripheral pulse waves, and an invasive blood pressure measuring device 4.

[0037] The non-invasive blood pressure measuring device 2 is a device that measures the blood pressure of a subject by a non-invasive blood pressure (NIBP) measurement method, and is equipped with a cuff 21, an exhaust valve 22, a pressure pump 23, a pressure sensor 24, a cuff pressure detection unit 25, and an A / D converter 26.

[0038] Specifically, as shown in FIG. 2, the non-invasive blood pressure measuring device 2 measures blood pressure by attaching a cuff 21 to the upper arm of a subject.

[0039] The inside of cuff 21 is opened or closed to the atmosphere by opening or closing exhaust valve 22. Exhaust valve 22 is opened or closed based on a control signal output from blood volume measuring device 1. Air is supplied to cuff 21 from pressure pump 23. The supply of air is controlled based on the control signal output from blood volume measuring device 1.

[0040] In addition, a pressure sensor 24 (cuff pulse wave sensor) is connected to the cuff 21, and the output of this sensor is detected by a cuff pressure detection unit 25. The output of the cuff pressure detection unit 25 is converted into a digital signal by an A / D converter 26 and input to the NIBP pulse pressure measurement means 11 of the blood volume measurement device 1.

[0041] The exhaust valve 22, the pressure pump 23, the pressure sensor 24, the cuff pressure detection unit 25, and the A / D converter 26 are provided in a biological information monitor main body (bedside monitor) M1, which is the main body of the biological information monitor M shown in FIG.

[0042] The pulse wave transit time detecting device 3 includes a reference point measuring means 31, a photoelectric pulse wave detecting sensor 32, a pulse wave detecting section 33, and an A / D converter .

[0043] The reference point measuring means 31 measures the time point of an R wave occurrence in an electrocardiogram as a reference point of a time interval. The output of the reference point measuring means 31 is converted into a digital signal by an A / D converter and input to the heart rate calculating means 12 and the pulse wave transit time measuring means 13 of the blood volume measuring device 1.

[0044] Specifically, the reference point measuring means 31 is composed of electrocardiogram electrodes 31a (electrocardiogram measuring means) attached to the chest of the subject as shown in Fig. 2. Data measured by the electrocardiogram electrodes 31a is wirelessly transmitted from a measurement data transmitter 65 electrically connected to the electrocardiogram electrodes 31a to the biological information monitor main body M1. The transmitted measurement data is converted into a digital signal by an A / D converter in the biological information monitor main body M1 and input to the heart rate calculation means 12 and the pulse wave transit time measuring means 13. In this way, an electrocardiogram waveform as shown in Fig. 4(a) is obtained. The function of the measurement data transmitter 65 may be modularized and built into the biological information monitor main body M1.

[0045] 2, photoplethysmography sensor 32 is attached to a peripheral part of the subject, such as a finger, to measure the pulse wave. Photoplethysmography sensor 32 is electrically connected to measurement data transmitter 65, and data measured by photoplethysmography sensor 32 is wirelessly transmitted to biological information monitor main body M1.

[0046] This measurement data is sent to a pulse wave detection unit 33 in the vital sign monitor main body M1, which detects the pulse wave (photoelectric pulse wave) at the site where the subject is attached. The output of the pulse wave detection unit 33 is converted into a digital signal by an A / D converter 34 and input to the pulse wave propagation time measurement means 13 of the blood volume measuring device 1. In this way, a photoelectric pulse wave waveform (peripheral waveform) as shown in Fig. 4(d) is obtained.

[0047] The invasive blood pressure measuring device 4 measures blood pressure by an invasive blood pressure (IBP) method, i.e., by inserting a catheter into the blood vessel of the subject. Blood pressure data measured by the invasive blood pressure measuring device 4 is input to the invasive blood pressure pulse pressure measuring means 16 of the blood volume measuring device 1.

[0048] The blood volume measuring device 1 is a device for measuring cardiac output, and includes an NIBP pulse pressure measuring means 11, a heart rate calculating means 12, a pulse wave transit time measuring means 13, a cardiac output calculating means 14, a subject-specific coefficient calculating means 15, and an invasive blood pressure pulse pressure measuring means 16. The blood volume measuring device 1 is provided inside the vital sign monitor main body M1.

[0049] The NIBP pulse pressure measuring means 11 measures the NIBP pulse pressure based on the blood pressure data measured by the non-invasive blood pressure measuring device 2. The NIBP pulse pressure is calculated from the difference between the systolic (maximum) blood pressure value and the diastolic (minimum) blood pressure value. The measured NIBP pulse pressure is input to the subject-specific coefficient calculating means 15.

[0050] The heart rate calculation means 12 calculates the number of beats per minute (heart rate) based on the reference point (time point of R wave occurrence) measured by the reference point measurement means 31. The calculated heart rate is input to the cardiac output calculation means .

[0051] The pulse wave transit time measuring means 13 measures the pulse wave transit time (PWTT) based on the reference point (time point of R wave generation) measured by the reference point measuring means 31 and the peripheral waveform detected by the photoelectric pulse wave detection sensor 32. The measured pulse wave transit time is input to the cardiac output calculating means 14 and the subject-specific coefficient calculating means 15. The pulse wave transit time is indicated by the time difference from the R wave of the electrocardiogram to the rising edge of the peripheral pulse wave, as shown in FIG. 4.

[0052] The subject-specific coefficient calculation means 15 calculates a subject-specific coefficient based on biological information parameters including at least one of the NIBP pulse pressure measured by the NIBP pulse pressure measurement means 11, the heart rate calculated by the heart rate calculation means 12, and the pulse wave transit time measured by the pulse wave transit time measurement means 13. The calculated coefficient is input to the cardiac output calculation means 14.

[0053] The cardiac output calculation means 14 calculates the cardiac output based on bioinformation parameters including at least one of the heart rate calculated by the heart rate calculation means 12 and the pulse wave propagation time measured by the pulse wave propagation time measurement means 13, and a coefficient calculated by the subject-specific coefficient calculation means 15.

[0054] Moreover, input means 5 is connected to blood content measuring device 1, and necessary data is externally input by a medical professional via input means 5. Moreover, a display unit 61 is connected to blood content measuring device 1, and the measured biological information of the subject is displayed on display unit 61. Furthermore, an alarm unit 62 is connected to blood content measuring device 1, and an alarm is issued via alarm unit 62 when an abnormality is detected in the measured biological information.

[0055] Next, a blood volume measurement method for calculating the estimated continuous cardiac output (esCCO) from Equation 16 will be described with reference to the flowchart of FIG.

[0056] The subject-specific coefficients α, β, and K are determined by calibration to calculate esCCO. Calibration of α and β is performed when there is no increase in pulse pressure (PP) due to administration of vasoconstrictors, etc.

[0057] First, the initial value of coefficient α is read (step 1). Next, PWTT (pulse wave transit time) and HR (heart rate) are obtained by actual measurement (step 2). PWTT is calculated and obtained from the R wave of the electrocardiogram and the photoelectric pulse wave measured by the photoelectric pulse wave detection sensor 32. HR is calculated and obtained from the R wave of the electrocardiogram measured by the reference point measurement means 31.

[0058] Next, it is determined whether the coefficient β is present (step 3). α and β are coefficients specific to the subject that are experimentally determined. If the coefficient β is not present in step 3 (step 3: No), a message requesting that the calibration blood pressure be measured is displayed on the display unit 61 (step 4).

[0059] Next, the calibration blood pressure is measured, and the instantaneous values ​​of PP (pulse pressure), PWTT, and HR (also called first biological information parameters), and the moving average values ​​of PP, PWTT, and HR (also called second biological information parameters) are calculated as calibration parameters (step 5). Here, the instantaneous value means an instantaneous value in time series data, and the moving average value means an average value for a certain interval in time series data. The certain interval in the moving average value is, for example, 3 to 10 minutes. Moreover, PP is a value measured by the NIBP pulse pressure measuring means 11 or the invasive blood pressure pulse pressure measuring means 16.

[0060] Next, a baseline determination is performed to determine whether the difference between the calculated instantaneous value and the moving average value is equal to or less than a predetermined threshold value Th (step 6), and if the difference between the instantaneous value and the moving average value is greater than the threshold value Th (step 6: No), the instantaneous value and the moving average value are calculated again (step 5). If the difference between the instantaneous value and the moving average value is equal to or less than the threshold value Th (step 6: Yes), the PP, PWTT, and HR are stored as PP1, PWTT1, and HR1, respectively, in a register (not shown) in the subject-specific coefficient calculation means 15 (step 7).

[0061] Here, the instantaneous value and moving average value of the calibration parameter will be specifically described with reference to Fig. 5. Fig. 5 is a graph showing the relationship between the instantaneous value and moving average value of PWTT, which is an example of a calibration parameter. At times t1 and t2 (t2>t1), the absolute value of the difference between the instantaneous value of PWTT and the moving average value of PWTT is △PWTT. t1 , △PWTT t2 It is expressed as:

[0062] For example, if instantaneous noise occurs at time t1, the noise component is superimposed on the instantaneous value, and the noise component is superimposed on the moving average with a delay (a delay occurs). Therefore, at time t1, the instantaneous value and the moving average value greatly differ. In this way, the timing when the instantaneous value and the moving average value greatly differ, that is, △PWTT t1 If calibration is performed when esCCO is large, the calculated esCCO values ​​before and after calibration will differ significantly, reducing the accuracy of esCCO.

[0063] Therefore, △PWTT t1 If is less than the predetermined threshold Th, calibration is performed at time t1, and △PWTT t1 If the difference between the instantaneous value of PWTT and the moving average value of PWTT at time t2 is less than the predetermined threshold value Th, calibration is not performed at time t1, and the instantaneous value and the moving average value of PWTT are calculated again at time t2. t2 If is less than or equal to the predetermined threshold Th, calibration is performed at time t2. t2 If is greater than the predetermined threshold value Th, no calibration is performed at time t2, and the instantaneous value and the moving average value are calculated again.

[0064] A method for setting the threshold value Th will be described with reference to Fig. 6. Fig. 6 is a graph showing the relationship between the threshold value Th and the time elapsed since the start of moving average measurement. The threshold value Th may be a fixed value or a variable value. Fig. 6(a) shows the case where the threshold value Th is a fixed value, and Fig. 6(b) shows the case where the threshold value Th is a variable value.

[0065] As shown in (a) of Fig. 6, when the threshold value Th is a fixed value, calibration can be performed in a range in which the difference between the instantaneous value and the moving average value is always equal to or less than the threshold value Th. On the other hand, within, for example, one minute after the start of the moving average measurement, there are few cases in which the instantaneous value and the moving average value greatly deviate from each other as shown at time t1 in Fig. 5. Therefore, there is a risk that the baseline determination will not function effectively within a predetermined time after the start of the moving average measurement.

[0066] In contrast, as shown in (b) of FIG. 6, if the threshold value Th at the start of the moving average measurement is set to a lower value than the fixed value, and the threshold value Th is increased according to the elapsed time from the start of the moving average measurement to time t3 (for example, 1 minute) to widen the allowable range, the baseline determination is performed more strictly from the start of the moving average measurement to time t3, so that the baseline determination can function effectively. This makes it possible to maintain the calculation accuracy of esCCO even if the time required for esCCO calibration is shortened. In the example shown in (b) of FIG. 6, the threshold value Th is set to a constant value after time t3.

[0067] Returning to the explanation of the flowchart in Figure 3, the stored values ​​of PP1 and PWTT1 and the initial value α read in at step 1 are substituted into the formula β=PP1-α*PWTT1 to calculate the coefficient β (step 8). This formula is derived from formulas 4 and 14. After calculating the coefficient β, the process proceeds to step 15, where it is determined whether or not the coefficient K is present.

[0068] On the other hand, if the coefficient β is present in step 3 (step 3: Yes), a determination is made as to whether or not to recalibrate the initial value α read in step 1 (step 9). If the recalibration of α is not performed in step 9, the process proceeds to step 15, where a determination is made as to whether or not the coefficient K is present.

[0069] In step 9, if recalibration of α is to be performed, a message requesting measurement of a calibration blood pressure is displayed on the display unit 61 (step 10).

[0070] Next, similarly to steps 5 to 7, the calibration blood pressure is measured, and the instantaneous values ​​of PP (pulse pressure) and PWTT, and the moving average values ​​of PP, PWTT, and HR are calculated (step 11). It is determined whether the difference between the calculated instantaneous value and the moving average value is equal to or less than a predetermined threshold value (step 12). If the difference between the instantaneous value and the moving average value is greater than the threshold value (step 12: No), the instantaneous value and the moving average value are calculated again (step 11). If the difference between the instantaneous value and the moving average value is equal to or less than the threshold value (step 12: Yes), the PP, PWTT, and HR are stored as PP2, PWTT2, and HR2, respectively, in a register (not shown) in the subject-specific coefficient calculation means 15 (step 13).

[0071] Next, the coefficients α and β are calculated from the following two equations using PP1, PWTT1, and PP2, PWTT2 stored in the register (step 14). PP1=αPWTT1+β (Equation 17), PP2=αPWTT2+β (Equation 18)

[0072] Next, if the determination in step 9 is NO, or after the processes in steps 8 and 14, it is determined whether or not the coefficient K is present (step 15).

[0073] If the coefficient K is not available in step 15 (step 15: No), a request to input a CO value for calibration is displayed on the display unit 61 (step 16). Then, it is determined whether a CO value for calibration has been input (step 17), and if not (step 17: No), the system waits until it is input. On the other hand, if a CO value has been input (step 17: Yes), the input CO value is stored as CO1 in a register (not shown) in the subject-specific coefficient calculation means 15 (step 18).

[0074] Next, the stored CO1 and the above calculated α, β, PWTT1, and HR1 are substituted into the following equation to calculate the coefficient K (step 19). K=CO1 / ((α*PWTT1+β)*HR1) (Equation 19) Incidentally, Equation 19 is derived from the following two equations. K=CO1 / (PP1*HR1) (Equation 20) PP1=α*PWTT+β (Equation 21)

[0075] The coefficients α, β, and K found by calibration are then substituted into equation 15 to calculate esCCO (step 20). If coefficient K is found in step 15 (step 15: Yes), the process also proceeds to step 20 and esCCO is calculated. In this way, by performing calibration at an appropriate timing where the instantaneous value and the moving average value do not diverge significantly, large fluctuations in the calculated cardiac output before and after calibration can be prevented, and the subject's cardiac output can be accurately calculated.

[0076] The calculated esCCO is displayed on the display unit 61 (step 21). Then, the process returns to step 2, and the above-mentioned processing is sequentially repeated.

[0077] As described above, according to the blood volume measurement method and the measurement device of the embodiment, the cardiac output is calculated using a moving average value, making it less susceptible to the effects of momentary noise, and the calculation value of cardiac output is prevented from fluctuating greatly before and after calibration by performing calibration at an appropriate timing where the instantaneous value and the moving average value do not deviate greatly as shown in steps 6 to 8 and steps 12 to 14. This allows the cardiac output of the subject to be calculated accurately.

[0078] Although the embodiment of the present disclosure has been described above, it goes without saying that the technical scope of the present disclosure should not be interpreted as being limited by the description of the embodiment. The present embodiment is merely an example, and it is understood by those skilled in the art that various modifications of the embodiment are possible within the scope of the invention described in the claims. The technical scope of the present disclosure should be determined based on the scope of the invention described in the claims and its equivalents.

[0079] For example, in step 5 in the biological information monitor M according to the present embodiment, PP and PWTT are set as the first biological information parameters, and PP, PWTT, and HR are set as the second biological information parameters as the calibration parameters, but at least one of PP and PWTT may be set as the first biological information parameter, and at least one of PP, PWTT, and HR may be set as the second biological information parameter. Note that the second biological information parameter includes at least one parameter included in the first biological information parameter.

[0080] In addition, in steps 5 and 6 in the biological information monitor M according to this embodiment, an example has been shown in which the instantaneous values ​​of PP and PWTT and the moving average values ​​of PP, PWTT and HR are calculated, and it is determined whether or not the difference between the calculated instantaneous values ​​and the moving average values ​​is equal to or less than a predetermined threshold value Th, but the subject of the determination is not limited to the difference between the instantaneous values ​​and the moving average values. A first moving average value in a first predetermined interval ta of PP and PWTT, and a second moving average value in a second predetermined interval tb longer than the first predetermined interval Ta of PP, PWTT and HR may be calculated, and it may be determined whether or not the difference between the calculated first moving average value and the second moving average value is equal to or less than a predetermined threshold value Th.

[0081] Moreover, each process in the biological information monitor M according to this embodiment can be realized as a computer program that runs on the blood volume measuring device 1, the non-invasive blood pressure measuring device 2, and the pulse wave transit time detecting device 3.

[0082] The program can be stored in a non-transitory computer-readable medium and read by the computer. Examples of the non-transitory computer-readable medium include a magnetic recording medium, a magneto-optical recording medium, a CD-ROM, a CD-R, a CD-R / W, and a semiconductor memory (including an EPROM and a flash ROM). The program may also be read by the computer by various types of temporary computer-readable media. Examples of the temporary computer-readable medium include an electric signal, an optical signal, and an electromagnetic wave. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or via a wireless communication path. [Explanation of symbols]

[0083] M: Vital Information Monitor 1: Blood volume measuring device 2: Non-invasive blood pressure measuring device 3: Pulse wave transit time detector 4: Invasive blood pressure measuring device 5: Input method 11: NIBP pulse pressure measurement means 12: Heart rate calculation method 13: Pulse wave transit time measuring means 14: Cardiac output calculation means 15: Subject-specific coefficient calculation means 16: Invasive blood pressure pulse pressure measuring means

Claims

1. A blood volume measurement method for calculating cardiac output from a biological information parameter of a subject, comprising: a first measuring step of measuring a first value in a predetermined section of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject; a second measuring step of measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination step of determining whether a difference between the measured first value and the measured second value is equal to or less than a threshold value; a calibration step of calculating a coefficient specific to the subject based on the second value when the difference between the first value and the second value is determined to be equal to or less than the threshold value in the baseline determination step; A blood volume measuring method comprising: a calculation step of calculating the cardiac output based on the first value and a coefficient specific to the subject calculated in the calibration step.

2. 2. The method of claim 1, wherein the first value is an instantaneous value and the second value is a moving average value.

3. The method of claim 1 , wherein the threshold is variable.

4. The method for measuring blood volume according to claim 3 , wherein the threshold value increases with the elapsed time from the start of the second value measuring step.

5. In the calculation step, the cardiac output is calculated by the formula CO=K(α*PWTT+β)*HR, CO represents cardiac output, PWTT represents pulse wave transit time, HR represents heart rate, and α, β, and K each represent a coefficient specific to the subject.

2. The method of claim 1 .

6. A blood volume measurement device that calculates cardiac output from a biological information parameter of a subject, a first measurement means for measuring a first value of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject in a predetermined section; A second measuring means for measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination means for determining whether a difference between the measured first value and the measured second value is equal to or smaller than a threshold value; a calibration means for calculating a coefficient specific to the subject based on the second value when the baseline determination means determines that the difference between the first value and the second value is equal to or smaller than the threshold value; a calculation means for calculating the cardiac output based on the first value and a coefficient specific to the subject calculated by the calibration means.

7. On the computer, a first measuring step of measuring a first value of a first biological information parameter including at least one of a pulse wave transit time and a pulse pressure of the subject in a predetermined section; a second measuring step of measuring a second value of a second biological information parameter including at least one of a pulse wave transit time, a heart rate, and a pulse pressure of the subject in a section longer than the predetermined section; a baseline determination step of determining whether a difference between the measured first value and the measured second value is equal to or less than a threshold value; a calibration step of calculating a coefficient specific to the subject based on the second value when the difference between the first value and the second value is determined to be equal to or less than the threshold value in the baseline determination step; a calculation step of calculating a cardiac output based on the first value and a coefficient specific to the subject calculated in the calibration step.

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