JP3662683B2 - Cardiac output estimation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cardiac output estimation device that estimates the amount of blood pumped out of a heart of a living body, that is, the cardiac output.
[0002]
[Prior art]
Since the blood circulation state of the living body is extremely important for the maintenance of the life of the living body, it is necessary to grasp the blood circulation state using the blood pressure value or the like during surgery or intensive care with general anesthesia of the living body. ing. However, since a general automatic blood pressure measuring device determines a blood pressure value based on a change in Korotkoff sound or pulse wave generated in the process of changing the compression pressure of a part of a living body using a cuff, Not only does it take several tens of seconds to measure the value, but the measurement cycle is at least several minutes to avoid the effects of congestion, and there is a risk that it will be delayed to notice changes in the condition of the living body.
[0003]
On the other hand, for example, as described in PCT Application Publication No. WO 88/04910, a pressure pulse wave generated in an artery of a living body is detected for each beat, and the pressure pulse wave is detected from a preset relationship. There has been proposed a continuous blood pressure monitoring apparatus that estimates a blood pressure value of a living body for each beat based on the size. According to this, since the blood pressure value of the living body is estimated for each beat, it is possible to quickly know the change in the blood pressure value of the living body.
[0004]
[Problems to be Solved by the Invention]
However, since the blood flow volume of the living body, that is, the cardiac output is not in a one-to-one relationship with the blood pressure value, there may be a case where the blood pressure value is not sufficient even if it is sufficient. For example, if peripheral vascular resistance increases due to the influence of nerves or drugs, the blood pressure value also increases due to weak pulsation of the heart. In such a case, the cardiac output may not be sufficient. is there. Therefore, there are cases where the living body cannot be sufficiently monitored only by monitoring the blood pressure value with the conventional continuous blood pressure monitoring device.
[0005]
The present invention has been made in the background as described above, and an object thereof is to provide a cardiac output estimation device capable of continuously estimating cardiac output in a non-invasive manner. .
[0006]
[Means for Solving the Problems]
As a result of various investigations on the basis of the above circumstances, the present inventors have expressed the degree of fall of the diastolic waveform of the biological pressure pulse wave as a time constant, which corresponds to the peripheral resistance. Therefore, it was found that the cardiac output can be estimated based on the time constant and the blood pressure value at that time. The present invention has been made based on such findings.
[0007]
That is, the gist of the present invention is a cardiac output estimation device that estimates the amount of blood pumped from the heart of a living body, and (a) detects a pressure pulse wave generated in the artery of the living body. A pressure pulse wave detecting device, (b) a blood pressure value determining means for determining a blood pressure value of the living body when the pressure pulse wave detected by the pressure pulse wave detecting device is generated, and (c) the pressure pulse wave detecting device. A diastole determining means for determining the diastole of the pressure pulse wave from the shape of the pressure pulse wave detected by (d), and (d) the time constant of the waveform of the diastole pressure pulse wave determined by the diastole determining means. Based on the diastolic waveform time constant calculating means for calculating (e) the time constant calculated by the diastolic waveform time constant calculating means and the blood pressure value determined by the blood pressure value determining means. And a cardiac output calculating means for calculating the amount.
[0008]
【The invention's effect】
In this way, the cardiac output calculating means calculates the cardiac output based on the time constant calculated by the diastolic waveform time constant calculating means and the blood pressure value determined by the blood pressure value determining means. Calculated. Therefore, according to the cardiac output estimation apparatus of the present invention, the cardiac output is continuously estimated non-invasively, and the reliability of monitoring of the circulatory state of the living body is improved.
[0009]
Other forms of the invention
Preferably, the blood pressure value determining means determines an average blood pressure value of the living body, and the cardiac output calculating means is a product of the average blood pressure value and the reciprocal of the time constant. Based on the above, the cardiac output is calculated. Preferably, the blood pressure value determining means determines a blood pressure waveform corresponding to the pressure pulse wave of the living body, and the cardiac output calculating means includes a plurality of sections for dividing the blood pressure waveform. The cardiac output is calculated based on the integral value of the product of each value and the reciprocal of the time constant. In any of the above cases, the cardiac output is continuously estimated.
[0010]
Preferably, the pressure pulse wave detection device includes a pressure pulse wave sensor having a pressure detection element on a flat pressing surface that presses an artery located directly under the skin of the living body, and a flatness of the pressure pulse wave sensor. A pressure device that presses the pressure pulse wave sensor until a part of the arterial wall just below the skin is flattened by the pressing surface, and detects the pressure pulse wave in the artery without blood pressure It is. In this way, there is an advantage that the influence of the tension of the artery wall of the artery is suppressed and the shape of the pressure pulse wave corresponding to the pressure in the artery can be obtained.
[0011]
Preferably, the diastolic determination means detects a minimum inclination point in the diastolic waveform after the aortic valve closing time of the pressure pulse wave detected by the pressure pulse wave detection device, and the waveform of the pressure pulse wave Of these, the part after the minimum inclination point is determined as the diastole. In this way, there is an advantage that the start point of the diastole is determined as early as possible and the calculation accuracy of the time constant is improved. The diastolic determination means sequentially calculates a differential point in the diastolic waveform using a smooth differential equation, and determines the minimum point of the differential value as the minimum inclination point.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a circuit configuration of a cardiac output estimation device 8 to which the present invention is applied.
[0013]
In the cardiac output estimation device 8 of FIG. 1, a rubber bag is provided in a cloth belt-like bag, and the cuff 10 is wound around the upper arm 12 of a patient, for example, and the cuff 10 is connected to the cuff 10 via a pipe 20. A connected pressure sensor 14, a switching valve 16, and an air pump 18 are provided. The switching valve 16 has a pressure supply state that allows supply of pressure into the cuff 10, a slow discharge state that gradually discharges the inside of the cuff 10, and a quick discharge state that rapidly discharges the inside of the cuff 10. It is configured to be switched to one state.
[0014]
The pressure sensor 14 detects the pressure in the cuff 10 and supplies a pressure signal SP representing the pressure to the static pressure discrimination circuit 22 and the pulse wave discrimination circuit 24, respectively. The static pressure discriminating circuit 22 includes a low-pass filter, discriminates a cuff pressure signal SK representing a steady pressure, that is, a cuff pressure included in the pressure signal SP, and electronically controls the cuff pressure signal SK via an A / D converter 26. Supply to device 28. The pulse wave discriminating circuit 24 includes a band-pass filter, discriminates the pulse wave signal SM ₁ that is a vibration component of the pressure signal SP in terms of frequency, and the pulse wave signal SM ₁ is electronically controlled via the A / D converter 30. 28. The cuff pulse wave represented by the pulse wave signal SM ₁ is a pressure vibration wave generated from the brachial artery (not shown) and transmitted to the cuff 10 in synchronization with the heartbeat of the patient.
[0015]
The electronic control unit 28 includes a CPU 29, a ROM 31, a RAM 33, and a so-called microcomputer having an I / O port (not shown). The CPU 29 has a storage function of the RAM 33 according to a program stored in the ROM 31 in advance. By executing signal processing while using, a drive signal is output from the I / O port to control the switching valve 16 and the air pump 18.
[0016]
The pressure pulse wave detection device 34 is in a state where the open end of the housing 36 that forms a container faces the body surface 38 at the wrist 42 on the downstream side of the artery of the upper arm 12 with or without the cuff 10 attached. The attachment band 40 is detachably attached to the wrist 42. A pressure pulse wave sensor 46 is provided inside the housing 36 through a diaphragm 44 so as to be relatively movable and projectable from the open end of the housing 36. A pressure chamber 48 is formed by the housing 36 and the diaphragm 44 and the like. Has been. In the pressure chamber 48, pressure air is supplied from the air pump 50 via the pressure regulating valve 52, so that the pressure pulse wave sensor 46 has a pressing force P corresponding to the pressure in the pressure chamber 48. It is pressed against the body surface 38 by _HD . The housing 36, the diaphragm 44, and the like constituting the pressure chamber 48 function as a pressing device for the pressure pulse wave sensor 46.
[0017]
The pressure pulse wave sensor 46 is configured by, for example, a large number of semiconductor pressure-sensitive elements (not shown) arranged on a pressing surface 54 of a semiconductor chip made of single crystal silicon or the like. The pressure vibration wave generated from the radial artery 56 and transmitted to the body surface 38, that is, the pressure pulse wave P _A (t) as shown in FIG. _A pressure pulse wave signal SM ₂ representing the pressure pulse wave P _A (t) is supplied to the electronic control unit 28 via the A / D converter 58. The pressure pulse wave sensor 46 detects the pressure pulse wave while being pressed by the diaphragm 44 until a part of the tube wall of the radial artery 56 becomes flat by the flat pressing surface 54. Therefore, the pressure pulse wave signal SM ₂ roughly indicates the pressure in the radial artery 56.
[0018]
The CPU 29 of the electronic control unit 28 outputs drive signals to the air pump 50 and the pressure regulating valve 52 in accordance with a program stored in advance in the ROM 31 to press the pressure in the pressure chamber 48, that is, the pressure pulse wave sensor 46 against the skin. Adjust pressure. Thereby, in the continuous blood pressure monitoring, the optimum pressing force P _HDP of the pressure pulse wave sensor 46 is determined based on the pressure pulse wave sequentially obtained in the pressure change process in the pressure chamber 48, and the optimum pressing force of the pressure pulse wave sensor 46 is determined. The pressure regulating valve 52 is controlled so as to maintain the pressure P _HDP .
[0019]
FIG. 2 is a functional block diagram for explaining a main part of the control function of the electronic control device 28 in the blood pressure monitoring device 8. In FIG. 2, the blood pressure measuring means 70 is about 3 mmHg / sec after the cuff pressure control means 72 rapidly raises the compression pressure of the cuff 10 to a predetermined target pressure value P _CM (for example, a pressure value of about 180 mmHg). Within the slow pressure reduction period in which the pressure is gradually lowered at the speed, the systolic blood pressure value BP _SYS and the lowest blood pressure are measured using a well-known oscillometric method based on the change in the amplitude of the pulse wave represented by the sequentially collected pulse wave signal SM _1. The blood pressure value BP _{DIA and the} like are determined.
[0020]
Correspondence determining means 74 is the highest and lowest values of blood pressure value BP measured by blood pressure measuring means 70 and the highest value of pressure pulse wave P _A (t) detected by pressure pulse wave detecting device 34 at that time. By determining the coefficients α and β of the relational expression between the pressure pulse wave P _A (t) and the continuous blood pressure value EBP (t) expressed by Equation 1, based on the lowest value, the correspondence unique to the living body is determined. .
[0021]
[Expression 1]
EBP (t) = αP _A (t) + β
[0022]
The blood pressure value determining means 76 determines the continuous blood pressure value EBP (t), as shown in FIG. 3, based on the actual pressure pulse wave P _A (t) that is sequentially obtained from the correspondence relationship of Equation 1. The continuous blood pressure value EBP (t) on peak systolic blood pressure value EBP _SYS, because the lower peaks correspond to the lowest blood pressure value EBP _DIA, the blood-pressure determining means 76, the systolic blood pressure value EBP _SYS and the diastolic blood pressure value EBP _DIA Are obtained continuously for each beat and are displayed on the display 32 as necessary.
[0023]
The blood pressure value determining means 76 calculates the mean blood pressure EBP _MEAN from the continuous blood pressure value, that is, the blood pressure waveform EBP (t). This average blood pressure value EBP _MEAN is not an intermediate value between the upper peak value and the lower peak value of the blood pressure waveform EBP (t), but an average value (∫EBP (t) within one cycle of the continuous blood pressure value EBP (t). dt / 1 period, or ΣEBP (t) / number of samplings within one period), preferably in order to mitigate the influence of noise, for example, the average blood pressure value obtained sequentially for every predetermined number of periods, for example, about 10 beats A moving average blood pressure value is adopted.
[0024]
The diastolic determination means 80 obtains the time constant of the waveform corresponding to the cardiac diastole from the waveform representing the pressure pulse wave P _A (t), that is, the continuous blood pressure value EBP (t). Determine the start point of diastole after aortic valve closure. The timing of closing the aortic valve is limited to a certain range from the upper peak point of the above waveform (at time t _{0 in} FIG. 3), and an empirical rule is used that shows the steepest descent in the early diastole. The diastolic determination means 80 is set so that even the youngest person having the longest time from the upper peak point of the waveform to the aortic valve closing time (time t _{1 in} FIG. 3) is after the start of the diastole. Period A, for example, after a time of about 250 ms from the upper peak point, the minimum inclination point (maximum inclination point in absolute value) [d (P _A (t)) / dt)] _min, that is, at time t _{2 in} FIG. Is detected, the period corresponding to the diastole of the waveform is determined.
[0025]
In the diastolic determination means 80, the minimum slope [d (P _A (t)) / dt)] _min is preferably the minimum value of the differential value calculated by the smooth differential equation shown below. It is done. In this smooth differential equation, for example, as shown in FIG. 4, sampling data near a predetermined time point t _i within the diastole of the waveform is x _i−3 , x _i−2 , x _i−1 , x _i. when a _{x i + 1, x i +} 2, x i + 3, from equation 2 (the slope of the waveform) a differential value of the predetermined time t _i sub _i is determined. In Equation 2, T _s is a sampling period.
[0026]
[Expression 2]
sub _i = (x _{i + 1} + x _{i +2} + x _{i +3} -x _{i -3} -x _i -2 -x _i-1 ) / (12 × T _s )
[0027]
The diastolic waveform time constant calculating unit 82 calculates the time constant τ from the logarithmic curve of the waveform corresponding to the diastolic phase in the pressure pulse wave P _A (t) determined by the diastolic determining unit 80. For example, it is calculated using Equation 3. In Equation 3, P ₂ and P ₃ are the pressure values at two arbitrary points at both ends of the interval where the integration is performed in the waveform within the expansion period. In this embodiment, in order to improve the calculation accuracy of the time constant τ, P ₂ is set as the diastole start point (minimum slope point of the waveform), and P ₃ is set as the diastole end point (minimum point of the waveform). Note that Equation 3 expresses both sides of the approximate expression P _A (t) = A · e ^{−t / CR} (where τ = CR) for times 0 to t _d in the interval between P ₂ and P _3. It is derived by integrating. C represents vascular compliance, and R represents vascular peripheral resistance.
[0028]
[Equation 3]
τ = ∫P _A (t) dt / (P ₂ −P ₃ )
[0029]
The cardiac output calculating means 84 is preset based on the time constant τ calculated from the diastolic waveform by the diastolic waveform time constant calculating means 82 and the blood pressure value determined by the blood pressure value determining means 76. The cardiac output (relative value) Q _relative is calculated for each beat from the obtained mathematical formula 4. The relationship between the average stroke volume Q _AV , the average blood pressure P _AV , and the peripheral vascular resistance R can be expressed by R = P _AV / Q _AV while a concept similar to Ohm's law can be applied. Since τ is the product of the vascular compliance C and the peripheral vascular resistance R as described above, τ is expressed by τ = C · P _AV / Q _AV . By using this modified expression Q _AV = C · P _AV / τ, it is possible to calculate the average cardiac output Q _AV, that is, the cardiac output, but it is difficult to determine the compliance C of the blood vessel. Therefore, if it is assumed that the compliance C of the blood vessel of the living body is constant within a short time, the relative value Q _relative can be obtained by Expression 4 in which the compliance C is set to “1”, for example.
[0030]
[Expression 4]
Q _relative = P _AV / τ
[0031]
The display control means 86 calculates the cardiac output (relative value) Q _relative calculated for each beat by the cardiac output calculation means 84, for example, one beat along the time axis 88 as shown in FIG. A trend graph for connecting the calculated values to each other is displayed on the display 32. Further, bar-shaped marks indicating the systolic blood pressure value EBP _SYS and the diastolic blood pressure value EBP _DIA determined by the blood pressure value determining means 76 are continuously displayed along the common time axis 88, and the blood pressure value and the cardiac output Q _relative are displayed. Can be compared. The upper and lower ends of the bar-shaped marks indicate the maximum blood pressure value EBP _SYS and the minimum blood pressure value EBP _DIA , respectively.
[0032]
FIG. 6 and FIG. 7 are flowcharts for explaining a main part of the control operation in the electronic control device 28 of the cardiac output estimating device 8, which is repeatedly executed in a predetermined control cycle. FIG. 6 shows a blood pressure measurement routine, and FIG. 7 shows a cardiac output calculation routine.
[0033]
In FIG. 6, after an initial process for clearing a counter and a register (not shown) is executed in step SA <b> 1 (hereinafter, step is omitted), in SA <b> 2 corresponding to the cuff pressure control means 72, the switching valve 16 is in the pressure supply state. And the air pump 18 is driven to start the rapid pressure increase of the cuff 10 for blood pressure measurement. In subsequent SA3, whether a cuff pressure P _C is the target compression pressure P _CM or which is previously set to about 180mmHg is determined. If the determination at SA3 is negative, the cuff pressure P _C continues to rise by repeatedly executing the above SA2 and subsequent steps.
[0034]
However, if the determination of SA3 is affirmed due to the increase in the cuff pressure P _C , the blood pressure measurement algorithm is executed in SA4 corresponding to the blood pressure measurement means 70. That is, by stopping the air pump 18 and switching the switching valve 16 to the slow exhaust pressure state, the pressure in the cuff 10 is lowered at a predetermined moderate speed of about 3 mmHg / sec. In accordance with a well-known oscillometric blood pressure value determination algorithm based on the change in the amplitude of the pulse wave represented by the pulse wave signal SM ₁ sequentially obtained at _{1, the} maximum blood pressure value BP _SYS , the average blood pressure value BP _MEAN , and the minimum blood pressure value The BP _DIA is measured, and the pulse rate and the like are determined based on the pulse wave interval. Then, the measured blood pressure value and pulse rate are displayed on the display 32, and the switching valve 16 is switched to the rapid exhaust pressure state so that the inside of the cuff 10 is rapidly exhausted.
[0035]
Next, at SA5, one pressure pulse wave P _A (t) detected by the pressure pulse wave detector 34 is read, and then at SA6 corresponding to the correspondence determining means 74, the pressure is detected. Based on the peak value, that is, the maximum value and the minimum value of the pulse wave P _A (t) and the maximum blood pressure value BP _SYS and the minimum blood pressure value BP _DIA measured in SA4, their relationship EBP (t) = αP _A (t ) + Β is determined.
[0036]
In SA7, it is determined whether or not one pressure pulse wave P _A (t) detected by the pressure pulse wave detector 34 is newly read. If the determination of SA7 is negative, the execution of SA7 is repeated. If the determination is positive, in SA8 and SA9 corresponding to the blood pressure value determining means 76, the relationship EBP (t) = αP _A (t) Based on the actual pressure pulse wave P _A (t) from + β, a continuous blood pressure value, that is, a blood pressure waveform EBP (t), a maximum blood pressure value EBP _SYS , a minimum blood pressure value EBP _{DIA, and the} like are determined, and a blood pressure waveform EBP (t) The average blood pressure value EBP _MEAN within one cycle is determined.
[0037]
In SA10, it is determined whether or not a preset period of about 15 to 20 minutes, that is, a calibration period has elapsed since the blood pressure measurement by the cuff 10 was performed in SA4. If the determination of SA9 is negative, the continuous blood pressure measurement routine below SA7 is repeatedly executed, and the continuous blood pressure value, that is, the blood pressure waveform EBP (t) is continuously determined for each beat. In the case where the above determination is affirmed, the relationship EBP (t) = αP _A (t) + β is updated by executing SA2 and subsequent steps in order to redetermine the correspondence relationship.
[0038]
In cardiac output calculation routine of Figure 7, after one of the pressure pulse wave P _A (t) is read in SB1, the SB2 corresponding to the diastolic determining means 80, the pressure pulse wave P _A of (t) By detecting the minimum slope (maximum slope in absolute value) [d (P _A (t)) / dt)] _min after the set period A has elapsed from the upper peak point, that is, the time t _{2 in} FIG. The start point of the diastole of the waveform is determined. The two-dot chain line in FIG. 3 indicates the minimum inclination [d (P _A (t)) / dt)] _min .
[0039]
Next, in SB3 corresponding to the diastolic waveform time constant calculating means 82, a predetermined interval in the diastolic period of the pressure pulse wave P _A (t) determined in SB2, the minimum slope point in this embodiment (FIG. 3). lowest point from t ₂ time) of (in the t ₃ time points) to the section of FIG. 3 (time 0 to t _d), the time constant τ of the logarithmic curve in the section, the pressure value of t ₂ time points from the formula 3 calculated based on P ₂ and t ₃ time pressure value P ₃ of the.
[0040]
Next, at SB4, the average blood pressure EBP _MEAN determined by the blood pressure value determining means 76 is read. Subsequently, in SB 5 corresponding to the cardiac output calculation means 84, the time constant τ calculated from the diastolic waveform of the pressure pulse wave P _A (t) in SB 3 and the blood pressure value determination means 76 are determined. Based on the average blood pressure EBP _MEAN , the cardiac output (relative value) Q _relative (= P _AV / τ) is calculated for each beat from Equation 4 set in advance.
[0041]
Then, in SB6 corresponding to the display control means 86, the cardiac output (relative value) Q _relative calculated for each beat by the SB5 is set to one beat along the time axis 88 as shown in FIG. A trend graph that interconnects the values calculated for each is displayed on the display 32. Further, bar marks indicating the maximum blood pressure value EBP _SYS and the minimum blood pressure value EBP _DIA determined by the blood pressure value determining means 76 are continuously displayed along the common time axis 88, and the blood pressure value and the cardiac output Q _relative are displayed. Can be compared.
[0042]
As described above, according to this embodiment, the cardiac output calculation unit 84 (SB5) calculates the diastolic waveform time constant calculation unit 82 (SB3) from Equation 4 (Q _relative = P _AV / τ). The cardiac output Q _relative is calculated based on the time constant τ and the average blood pressure value EBP _MEAN determined by the blood pressure value determining means 76 (SA9). Therefore, according to the cardiac output estimation apparatus 8 of the present embodiment, the cardiac output Q _relative is continuously estimated non-invasively, and the reliability of monitoring of the circulatory state of the living body is improved.
[0043]
The blood pressure value determining means 76 (SA9) of this embodiment determines the average blood pressure value EBP _MEAN of the living body for each beat, and the cardiac output calculating means 84 (SB5) is the average blood pressure value. since calculates a cardiac output Q _relative to each one heartbeat based on the multiplication value of the reciprocal of the time constant τ and EBP _MEAN, cardiac output Q _relative is continuously estimated.
[0044]
In addition, the pressure pulse wave detection device 34 of the present embodiment includes a pressure pulse wave sensor 46 having a number of pressure detection elements on a flat pressing surface 54 that presses the radial artery 56 located directly under the skin of the living body, and the pressure thereof. A pressing device (36, 44) for pressing the pressure pulse wave sensor 46 until a part of the tube wall of the radial artery 56 just below the skin becomes flat by the flat pressing surface 54 of the pulse wave sensor 46; Since the pressure pulse wave P _A (t) in the radial artery 56 is detected non-invasively, the influence of the tension of the tube wall of the radial artery 56 is suppressed, and the pressure in the artery is reduced. There is an advantage that the shape of the corresponding pressure pulse wave P _A (t) can be obtained.
[0045]
Further, the diastolic determination means 80 (SB2) of the present embodiment is the minimum slope point in the diastolic waveform after the aortic valve closing timing of the pressure pulse wave P _A (t) detected by the pressure pulse wave detecting device 34, that is, [ d that _{(P a (t)) /} dt) ] detects the t ₂ time points in FIG. 3 is _min, and determining diastolic its minimum inclination point after one of the waveform of the pressure pulse wave P _a (t) Therefore, there is an advantage that the start point of the diastole is determined as early as possible and the calculation accuracy of the time constant τ is improved. In addition, the diastolic determination means 80 (SB2) sequentially calculates the differential point in the diastolic waveform using a smooth differential equation, and determines the minimum point of the differential value as the minimum slope point. Is suppressed, and the determination accuracy is improved.
[0046]
As mentioned above, although one Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.
[0047]
For example, the cardiac output calculation means 84 of the above-described embodiment calculates the cardiac output Q _relative for each beat based on the product of the average blood pressure value EBP _MEAN and the inverse of the time constant τ. However, by integrating the product of the instantaneous value of the continuous blood pressure value EBP (t) and the inverse of the time constant τ within one period of the waveform, the cardiac output Q _relative [= ∫ (1 / τ ) EBP (t) dt] may be calculated. In short, it is only necessary to calculate the cardiac output Q _relative based on the time constant τ calculated by the diastolic waveform time constant calculating means 82 and the blood pressure value determined by the blood pressure value determining means 76.
[0048]
In the above-described embodiment, the cardiac output Q _relative is calculated in real time for each beat, but may be calculated for every few beats or tens of beats.
[0049]
In the diastolic waveform time constant calculating means 82, the time constant τ is calculated in the diastolic waveform after the aortic valve closing time of the pressure pulse wave P _A (t), but the continuous blood pressure value EBP (t) The time constant τ may be calculated in the diastole waveform after the aortic valve closing time.
[0050]
In the above-described embodiment, the mean blood pressure value EBP _MEAN is determined for each beat by the blood pressure value determining means 76. However, it may be determined for each preset period longer than one beat. The average blood pressure value EBP (t) _MEAN may be calculated from the continuous blood pressure value EBP (t) by the blood pressure value determining means 76. Furthermore, instead of the average blood pressure value EBP _MEAN , the average blood pressure value determined from the cuff pressure when the maximum pulse wave amplitude is generated may be used for a predetermined period in the process of measuring blood pressure by the oscillometric method.
[0051]
In the above-described embodiment, the pressure pulse wave P _A (t) in the radial artery 56 is used as the pressure pulse wave of the artery at a predetermined site downstream of the aorta. The pressure pulse wave of the other part may be used. However, when pressed by the flat pressing surface 54 of the pressure pulse wave sensor 46, it is desirable to press until a part of the tube wall becomes flat, but try to press until a part of the tube wall becomes flat. In such a case, for example, the carotid artery is not possible because there is no hard backup, and it is desired that the carotid artery be backed up by bone or the like so that the artery does not escape. In this regard, the radial artery 56 or the dorsal artery is desirable.
[0052]
In the above-described embodiment, the blood pressure measuring means 70, the correspondence determining means 74, and the blood pressure value determining means 76 are provided. However, the pressure pulse wave P ₂ (t) output from the pressure pulse wave detecting device 34 is provided. When the absolute value is highly reliable and calibration based on the blood pressure value measured using the cuff 10 is not required, the blood pressure measuring means 70, the correspondence determining means 74, and the blood pressure determining means 76 are not provided. There is no problem.
[0053]
The present invention can be modified in various other ways without departing from the spirit of the present invention.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a circuit configuration of a cardiac output estimating apparatus according to an embodiment of the present invention.
FIG. 2 is a functional block diagram illustrating a main part of a control function of the electronic control unit 28 in the embodiment of FIG.
3 is a diagram showing an example of a pressure pulse wave detected by the pressure pulse wave detection device of the embodiment of FIG. 1; FIG.
4 is a diagram for explaining a smooth differential calculation used for obtaining the slope of a pressure pulse wave in the diastole determining means of FIG. 2. FIG.
FIG. 5 is a diagram showing a trend display of cardiac output displayed by the display control unit of FIG.
6 is a flowchart for explaining a main part of the control operation of the electronic control unit 28 in the embodiment of FIG. 1 and showing a blood pressure measurement routine. FIG.
7 is a flowchart for explaining a main part of the control operation of the electronic control unit 28 in the embodiment of FIG. 1, and showing a cardiac output calculation routine. FIG.
[Explanation of symbols]
34: pressure pulse wave detection device 46: pressure pulse wave sensor 54: pressure surface 76: blood pressure value determining means 80: diastolic period determining means 82: diastolic waveform time constant calculating means 84: cardiac output calculating means 86: display control means

Claims (5)

A cardiac output estimator that estimates the volume of blood pumped from the heart of a living body,
A pressure pulse wave detection device for detecting a pressure pulse wave generated in the artery of the living body;
A blood pressure value determining means for determining a blood pressure value of the living body at the time of occurrence of the pressure pulse wave detected by the pressure pulse wave detecting device;
From the shape of the pressure pulse wave detected by the pressure pulse wave detection device, diastole determination means for determining the diastole of the pressure pulse wave;
Diastolic waveform time constant calculating means for calculating the time constant of the waveform of the diastolic pressure pulse wave determined by the diastolic determining means;
A cardiac output calculating means for calculating a cardiac output based on the time constant calculated by the diastolic waveform time constant calculating means and the blood pressure value determined by the blood pressure value determining means. An apparatus for estimating cardiac output. The blood pressure value determining means determines an average blood pressure value of the living body, and the cardiac output calculating means is based on a product of the average blood pressure value and the reciprocal of the time constant. The cardiac output estimation apparatus according to claim 1, wherein the cardiac output is calculated. The blood pressure value determining means determines a blood pressure waveform corresponding to the pressure pulse wave of the living body, and the cardiac output calculating means is configured to determine individual values of a plurality of sections dividing the blood pressure waveform and the time. The cardiac output estimating apparatus according to claim 1, wherein the cardiac output is calculated based on an integral value of a multiplication value of a reciprocal of a constant. The pressure pulse wave detecting device includes a pressure pulse wave sensor having a pressure detection element on a pressing surface that presses an artery located directly under the skin of the living body, and an artery directly under the skin by a flat pressing surface of the pressure pulse wave sensor. A pressure device that presses the pressure pulse wave sensor until a part of the tube wall becomes flat, and detects the pressure pulse wave in the artery by non-invasive blood pressure. Cardiac output estimation device. The diastolic determination means detects a minimum slope point in the waveform after the aortic valve closing time of the pressure pulse wave detected by the pressure pulse wave detection device, and after the minimum slope point in the waveform of the pressure pulse wave The cardiac output estimating apparatus according to any one of claims 1 to 4, wherein the cardiac output is estimated to be diastole.

Images