JPS6335238A - Apparatus for meauring time constant characteristic of terminal blood vessel - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a blood vessel time constant for measuring the product of peripheral blood vessel compliance and its resistance based on blood flow or blood vessel-related electrical signals. This invention relates to a characteristic measuring device.

[Problems to be solved by the prior art and the invention] Conventionally, the arterial system has been considered as an elastic model using the wind keratin theory, and the blood volume of the elastic element (corresponding to its volume) is Q, and the blood pressure of that part is An analysis is performed to obtain C from the relationship dQ=cdP, where P is the compliance of the elastic element and C is the compliance of the elastic element, and it is also applied clinically, such as in the diagnosis of arteriosclerosis.

Furthermore, according to JP-A-58-216034, the above-mentioned elastic model was replaced with an electric circuit, and based on the volume pulse wave signal detected as an electric signal, arterial blood flow was determined as blood flowing in and out of the elastic elements of the blood vessel and flowing toward the distal side. A blood flow measurement device that can be separated into blood flow and blood flow has been proposed. However, the analysis of vascular properties' measurement of factors related to vascular resistance has two important implications:
In view of these points, the present invention provides a device for measuring time constant characteristics of peripheral blood vessels that electrically measures time constant characteristics corresponding to the product of peripheral vascular resistance and its compliance. With the goal.

[Means for solving problems]

As shown in Fig. 6, the arterial system can be considered by replacing it with an electric circuit formed by capacitance and electric resistance, and the electric impedance change Z in such a circuit is Z=kV... It has also been confirmed that it is given by (1) (K: constant of proportionality, ■=vascular volume)
, The differential value of the blood vessel volume with respect to time t is given by the difference between the outflow blood flow F6 to the measurement region and the outflow blood flow F6 from the more peripheral region as follows.

t On the other hand, the compliance C of the blood vessel is defined by the following equation.

Assuming that C is constant for blood pressure P=O~P,
The following equation is obtained from equation (3).

dV=cdP (4) By integrating this equation, we get the following.

Therefore, the following equation is obtained.

V=CP+K ・・・・・・・・・(6) Here,
K is an integral constant, and when P=0, since V=0, it becomes =O, so the following equation is obtained.

V=CP ・・・・・・・・・(7) As a result,
The outflow blood flow F from the measurement area to a more peripheral area is as follows.

Here, Pp: peripheral blood pressure; R: peripheral resistance pp approximates venous pressure and is sufficiently smaller than P, so Pp can be ignored; therefore, Fl is as follows.

R=□　・・・・・・・・・(9) By equations (7) and (9), ■ From equations (2) and (10), we get the following.

Setting α = 1/K and β = 1/KCR, the formula (
From 1) and (11), we have the following.

[1t CR=□ ・・・・・・・・・(13) β In actual measurements, F and Z are obtained as periodic functions F(t), 2(1) with respect to time t of heartbeat cycle T, Therefore, these are given as follows.

F(t)=ro+r(t) ・・・−−−・−・(
14) Z(t) = z0+ z(t) ---(
15) Here, fo and z6 are F(t) and Z(t)
The average value of each is as follows.

Therefore, if we rewrite equation (12) as a function of t, we get
Therefore, the following equation is obtained.

Since it is possible to set Z(0) = Z(T), the first term on the right side of this equation is 0, and therefore F6=βZo is obtained. Therefore, formulas (14), (15) and (19)
The following formula can be obtained from

As shown in Figure 7, this equation is expressed as p of f(t) detected by an electromagnetic blood flow meter in the central caudal artery of a rat.
The p-p value calculated from the -p value and the signal detected by the electrical impedance measuring device based on the right side of equation (18) is as follows:
It has been confirmed that a correlation exists over a wide range of levels. Therefore, in equation (20), dz(t
)ldt is rewritten as z'(t), 1=1+ and 1=
12 as follows.

f (t + ) = a z' (t +) + βz (t
+) ---(21)f (tZ) = (X Z
' (tZ) 10 βz (t2) --・= (22
) This results in the following based on Cramer's formula.

Here, Therefore, the time constant can be obtained by the following calculation as CR=α/β.

Therefore, in order to measure CR based on equation (26), the device for measuring time constant characteristics of peripheral blood vessels of the present invention is designed to measure blood flowing from the vicinity of the peripheral blood vessels to the peripheral side according to the heartbeat, as shown in FIG. A blood flow change signal detection means 1 that detects a change in flow as a blood flow change signal f(t), and an impedance change signal that detects a volume change due to heartbeat at the measurement site as an impedance change signal z(t). Detection means 2 and z
(t) to generate a differential signal z'(t), and a measurement time point setting for setting arbitrary two points in the heartbeat cycle, t1, t1, and t2, at which these signals are to be sampled. It is comprised of means 4 and time constant calculation means 5 which performs calculations based on equation (26).

[Effect]

The blood flow change signal detection means 1 detects r(t) of the measurement site, and the impedance change signal detection means 2 detects its z(t).
) is detected. The differentiating means 3 differentiates the detected z(t) to generate z'(t). The measurement time point setting means 4 uses a zero time constant to set arbitrary two points t+ and tZ in the heartbeat cycle based on r(t), z(t), z'(t) or a separate heartbeat signal. The calculation means 5 calculates the time point t.

blood flow change signal f(t+), impedance change signal Z(t+), and differential impedance change signal 2'
(t1) and blood flow change signal r (t L
), the measured values of the impedance change signal z(t2) and the differential impedance change signal z'(t2) are taken in, and the time constant is calculated according to equation (26).

[Embodiments of the invention]

FIG. 2 shows an embodiment of the present invention, which includes an ultrasonic blood flow meter 11 that detects blood flow in the radial artery, and an impedance plethysmograph 12 that detects changes in the arterial volume as impedance. , A that digitizes each detected value.
/Il converter 3.14 and a microcomputer 5 that takes in these digital signals and performs arithmetic processing.
It is composed of a cathode ray tube device 16 that monitors the waveform for performing this arithmetic processing, a printer 17 that prints out the preoperative waveform and the calculated OR value, and a numerical display 18 that displays the OR value.

The microcomputer 15 includes RAM, ROM,
By incorporating a CPU and the like, it is programmed to perform the circuit functions shown in FIG. That is, 1
51 is a storage means for storing sampling values of about 50 points of the blood flow signal F(t) and impedance signal 2(1) for at least one heartbeat cycle, and outputting them for signal processing; A heartbeat cycle detection means for detecting a heartbeat cycle T based on a signal, for example F(t); 153 a blood flow average value component calculation means for calculating a blood flow average value component 'L for one cycle to be measured; 154 a blood flow average value component calculation means Impedance average value component calculation means 155 calculates the impedance average value component Z+ for one cycle, and 155 calculates the blood flow change signal r by subtracting the blood flow average value component element o from the blood flow signal F(t) of the associated cycle. (
t), and 15B is the impedance average value component 2 from the impedance signal 2(1) of the period to which it belongs.
By subtracting ゜, the impedance change signal z(
t), the subtraction means 157 differentiates the output signal of this subtraction means to generate a differential impedance change signal 2'(
Differentiating means 158 for outputting 1) determines the measurement time by detecting the first zero point in the period to which the output signal of the subtracting means 155 belongs, and by detecting the second zero point of the output signal of the subtracting means 15B. Measurement time t1, t2
159 is a time constant calculating means that calculates a time constant based on equation (2B) using signal values at these points in time. Each of these parts 151 , 153 ,
At 155, the blood flow change signal detection means l shown in FIG.
51, 154, and 158 constitute impedance change signal detection means 2, and each section +51, 152, and +58 constitute measurement time point setting means 4.

During measurement, the microcomputer 15 controls the ^/D converter 13 based on an external command signal or intermittently.
．． Sampling data 9 F(t
) and 2 (1), hereafter, (7) CPU is the third
The processing operations of the circuit functions shown in the figure are performed. That is, as shown in FIG. 4, the first zero time of f(t) in the period T is tl and the first zero time of z(t) is tλ, and the sampling data f(tl) at these times is , f
(tl), z(tl), z(t2), z'(tl
), the time constant CR is calculated based on z'(t2). The waveform to be measured shown in FIG. 4 is monitored by the cathode ray tube device 18 and recorded on the printer 17. Further, the value of CR is displayed on the numerical display 18 and recorded on the printer 17.

In this embodiment, the values of tl and tZ can be set by extrapolation, for example, tl, t1, and t2 can be set as z(t
)=O and z'(t)=O, equation (26) becomes a simple arithmetic expression as follows.

FIG. 5 shows another embodiment in which the blood flow signal F(t) and the impedance signal 2(1) are connected to the capacitors 21 and 22.
By separating the DC component, the blood flow change signal f(
t) and an impedance change signal z(t) are generated. 23 is a heartbeat cycle detection circuit that detects the start and end points of a heartbeat based on the blood flow signal F(t). 24 is a peak detection circuit that defines the first measurement time point t1 by detecting the peak value of the blood flow signal F(t). 25 is a delay circuit that defines the next measurement time t2 by delaying this time t1 by a predetermined time Δt. 26
is a differentiation circuit that differentiates the impedance change signal z(t) using a capacitor and a resistance circuit. 27-28
are measurement time tl, f(t) at tl, z(t),
The sampling circuits 31 to 33 for the z'(t) signal are A/D converters that digitize the respective sampling values. 34 is these sampling data f(
tl), f(t2), Z(L), 2(t2), z
This is a CPU-based time constant calculation means that performs calculations based on equation (28) based on '(tl) and z'(t2). As a result, when a periodic signal is generated manually or automatically, CR is calculated based on the sampled value at the measurement point based on the peak value of the blood flow signal F(t) within that period. .

〔Effect of the invention〕

As described above, according to the present invention, by electrically detecting blood flow signals near peripheral blood vessels and volume changes in blood vessels, a value corresponding to the product of compliance and vascular resistance of peripheral blood vessels on the peripheral side is automatically determined. be able to measure it accurately. Therefore, it can be said that the present invention has great clinical significance in preventing arteriosclerosis and cerebral thrombosis.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the circuit configuration of a blood vessel time constant characteristic measuring device according to the present invention, FIG. 2 is a diagram showing the configuration of a time constant measuring circuit according to an embodiment of the present invention, and FIG. 3 is a diagram showing the operation of the microcomputer. Fig. 4 is a diagram showing its operating waveforms, Fig. 5 is a diagram showing the configuration of a time constant measurement circuit according to another embodiment, and Fig. 6 is a model of the electric circuit of the Windkera cell. The explanatory diagram and FIG. 7 are diagrams showing experimental data for confirming the feasibility of the present invention.

Claims (1)

[Scope of Claims] Blood flow change signal detection means for detecting, as an electrical signal f(t), a change in blood flow flowing from a measurement site near a peripheral blood vessel to a peripheral side in response to a heartbeat; impedance change signal detection means for detecting a volume change due to electrical impedance z(t); differentiating means for generating a differential signal z'(t) of the detected impedance change signal; measurement time point setting means for setting two time points t_1 and t_2;
Blood flow change signal f(t_1), impedance change signal z(t_1) and differential impedance change signal z'(t_1) at time t_1, blood flow change signal f(t_2) and impedance change signal at time t_2 z(t_
2) and differential impedance change signal z'(t_2)
Based on CR={f(t_1)z(t_2)-f(t_2)z(
t_1)/f(t_2)z'(t_1)-f(t_1)
z'(t_2)} (C: Compliance of peripheral blood vessels,
R: Peripheral vascular resistance).