SU1480811A1 - Device for measuring blood flow rate - Google Patents

Abstract

The invention relates to medical technology. A device for measuring blood flow velocity comprises a sensor 1, a generator of 2 signals, an amplifier 3, a filter 4, a level indicator. In order to improve the measurement accuracy while simplifying the design, a shaper 6 of the control signal, a mixer 7, a frequency meter 8 are inserted into it, and the sensor is made in the form of two cylindrical piezoelectric elements 9, 10 of variable cross section. The principle of operation is based on the fact that when a variable-section ultrasound signal of a fixed frequency is applied to a piezoelectric element, only a narrow portion of the piezoelectric element corresponding to the value of this frequency operates. If a piezoelectric element with a variable cross section and radius R of the radiating surface is fed into the frequency range ΔF _max , then when the frequency changes, the acoustic axis of the transducer will move along an arc of a circle of radius R and pass through the focus point 0. 4 Il.

Description

$ s

00

about

00

; /

5 w g

Fig /

The invention tends toward medical technology, namely, devices for measuring diagnostic parameters of the cardiovascular system.

The aim of the invention is to improve the measurement accuracy while simplifying the design.

FIG. I shows a block diagram of a device for measuring blood flow velocity in FIG. 2 - design features and functioning of the piezoelectric element included in the device sensor; Figures 3 and 4 show the transmission patterns of ultrasonic beams at different frequencies of the signal generated by the device generator.

A device for measuring blood flow velocity (Fig. 1) contains a sensor 1, to the input of which a signal generator 2 is connected, and an amplifier 3 connected to the output, a filter 4 and a level indicator 5 connected to the output, a control signal generator 6 the control input of the signal generator 2, the mixer 7, the first input of which is connected to the output of the signal generator 2, and the second input to the output of the amplifier 3, and the frequency meter 8 connected to the output of the filter 4, and the sensor 1 is made in the form of two cylindrical piezoelectric elements 9 and 1 About variable cross section The first piezoelectric element 9 is connected to the generator output 2 signals, and the second piezoelectric element 10 is connected to the input of the amplifier 3.

In a preferred embodiment of the device, the generator 2 can be made in the form of a controlled oscillator with electronic frequency tuning by a signal applied to its control input. Frequency meter 8 can be made in the form of a mean frequency meter. As a generator 6, a switch can be used that connects to the control input of the generator 2 a voltage corresponding to a logic zero level or a logic unit level. Filter 4 can be made in the form of a bandpass filter, and level indicator 5 - in the form of series-connected audio frequency amplifier and sound radiator (speaker). The sensor 1 is applied through a layer of wetting fluid 11 to the surface 12 of the patient in the vicinity of the blood vessel 13, in which the red blood cells 14 move in the direction indicated by the arrow in FIG. one .

The principle of operation of the device is based on the fact that when a variable-section ultrasound signal of a fixed frequency is applied to a piezoelectric element, only a narrow portion of the piezoelectric element corresponding in thickness to the frequency operates. The maximum eigenfrequency difference of the piezoelectric element is equal to

bf

 d 4 - d 2

(P

max j Lo,

where d is the average thickness of the piezoelectric element;

d is the maximum thickness of the piezoelectric element,

d - minimum thickness of the piezoelectric element}

f0 is the natural frequency of the piezoelectric element with thickness d. If the piezoelectric element has a variable cross section, as shown in FIG. 2, and with a radius R of the radiating surface, supply frequencies from the range, then when the frequency changes, the acoustic axis of the transducer moves along an arc of a circle of radius R and passes through the focus point O.

A device for measuring blood flow velocity works as follows.

The ultrasonic frequency signal from generator 2 is fed to the first piezoelectric element 9, as well as to the first input of the mixer 7. The ultrasonic signal passed through the wetting fluid 11 and the surface of the body 12 is reflected by red blood cells 14. The reflected signal is received by the second piezoelectric element 10, amplified by the amplifier 3 and fed to the second input of the mixer 7. The Doppler frequency signal, separated by a band-pass filter 4, is fed to the inputs of the level indicator 5 and the frequency meter 8. After measuring the average frequency for a specified time using a frequency generator 6, generator 2 is changed and the measurement process is repeated.

Using the level 5 indicator, the amplitude and frequency of the Doppler signal are monitored by ear, while achieving the maximum amplitude of the Doppler signal by changing the inclination of sensor I relative to body surface 12, which provides accurate guidance of sensor I focus point on vessel 13, in which blood flow velocity.

Consider the process of measuring blood flow velocity in more detail. When applying to the control input of the generator 2 from the generator 6 a signal of logical zero, the generator 2 produces an ultrasonic signal with a frequency

f f - - (d di} f ° 2 (d; f °

which enters the first piezoelectric element 9 of variable cross section. At this frequency, only the narrow section A corresponding to it in thickness is excited (Fig. 3). The ultrasonic signal emitted by the concave surface propagates along its acoustic axis in the form of a narrow beam. The ultrasonic signal reflected by the moving red blood cells 14 of the blood is received only by section A of the second piezoelectric element 10 corresponding to the thickness of the frequency. The electrical signal from the second piezoelectric element 10 is fed through amplifier 3 to the second input of the mixer 7, to the first input of which a signal comes from generator 2. From the output of the mixer 7, the signal goes to the input of filter 4, where the Doppler frequency signal is extracted.

fdi | vcos (A) ftf (3)

where v is the particle velocity

blood; c is the speed of ultrasound in

environment

/}, is the angle of incidence of the ultrasonic beam;

oi.t is the reflection angle of the ultrasonic beam;

f (is the frequency of the emitted ultrasonic signal (Fig. 3). When a signal of a logical unit is applied to the control input of generator 2, generator 2 produces an ultrasonic signal with frequency

fZ

cb

(four)

which arrives on the first piezo

Step 9. In this case, only the narrow section B corresponding to the thickness of this frequency is excited (Fig. 4). The ultrasonic signal emitted by the concave surface propagates along its acoustic axis in the form of a narrow beam. The signal reflected by the erythrocytes 14 is received according to the thickness of this frequency.

Section B of the second piezoelectric element 10.

Next, the electrical signal passes

along the circuit as well as in

case of frequency measurement fd ,,. The Doctler frequency is allocated at 154.

and,. | .co. (. e) (1

(five)

where $ g is the angle of incidence of the ultrasound beam;

2 shows the angle of reflection of the ultrasound beam (Fig. 4). Equations (3) and (5) constitute a system of two equations with two unknowns.

thirty

fd | L C08 (4-) ff.

fd - X-owls (,,

(6)

Considering that 35 ..b. (7)

where g is a parameter defined by the constructive structure of sensor 1, which depends on the angle between the axes of piezoelectric elements 9 and 10,

and using expressions (2) and (4), one can solve the system of equations (6) with respect to the blood flow velocity

45

v fd.

2fc

(eight)

H

The measurements of the fd and fdЈ values by the frequency meter 8 over a specified time, then using the formula (8) are (using previously prepared nomograms or tables, or using computer technology) the average linear velocity of blood flow.

The device has high accuracy in measuring blood velocity

FIG. g

Fi.Z

Claims (2)

Claim A device for measuring blood flow velocity, comprising a sensor, to the input of which a signal generator is connected, and an amplifier, and a filter and level indicator connected in series, characterized in that, in order to increase the measurement accuracy while simplifying the design, a shaper is introduced a control signal connected to the control input of the signal generator, a mixer, the first input of which is connected to the output of the signal generator, and the second input to the output of the amplifier, and a frequency meter connected to the filter output, and the sensor IR is made in the form of two cylindrical. piezoelectric elements of variable cross section, the first piezoelectric element connected to the output of the signal generator, and the second to the input of the amplifier. Wii. FIG. 2 i480811 Fig. 3 FIG. 9