JP2915343B2 - Blood flow measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a blood flow measuring device. In more detail, it is excellent in quickness of measurement, accuracy and reproducibility of measurement value accuracy, and is easy to operate, zero correction of measurement value, fine adjustment of probe measurement angle and accurate advance of blood vessel diameter at measurement. The present invention relates to a blood flow measurement device that does not require investigation.

[0002]

2. Description of the Related Art Conventionally, many types of blood flow measuring devices have been proposed and used for surgical operations and other medical procedures. Almost all of these blood flow measurement devices or blood flow meters use the following three types of methods as their measurement principles. That is, electromagnetic flow measurement,
A flow rate measurement method using the Doppler principle and a flow rate measurement method using the transit time principle.

The electromagnetic flow measurement method is based on the principle that blood and other body fluids are electrically conductive, and a voltage is generated in an electric circuit when an electrically conductive substance such as blood moves in a direction perpendicular to a magnetic field. The generated voltage is proportional to the flow rate. In this electromagnetic flow measurement method, a clip-on type device is generally used as a blood flow detection sensor, and in order to obtain accurate measurement values, it is necessary to make good contact between the blood vessel wall and the electrodes during measurement. In addition, there is a problem that skill is required to select and select a probe having an appropriate inner diameter, and it takes time, time, and the like to perform preliminary investigation, selection, and setting. In addition, the measured value always requires zero point compensation, and the potential at this zero flow point tends to drift,
Skillful techniques are required to obtain accurate measurement values. Furthermore, in this method, the measurement depends on the hematocrit of the blood.

[0004] The Doppler principle flow velocity measurement method utilizes the backscattering of ultrasonic waves, and the Doppler shift of a wave is proportional to the moving speed of an object. In blood, the frequency shift differs according to the difference in the moving speed of blood, and the faster the moving speed, the greater the frequency shift. Recent advances in technology have provided measurement devices with an excellent signal / noise ratio for a wide range of frequencies, and thus good detection sensitivity. This method has an advantage that the contact area between the probe and the blood vessel may be small, and therefore, the method can be applied to a thin blood vessel. In addition, there is an advantage that the output can be increased and measurement can be performed even when the vessel does not directly contact the blood vessel wall. However, since the Doppler shift varies in proportion to the incident angle of the ultrasonic wave, measurement of the volume flow rate, for example, expressed in ml / min presents a troublesome problem in this method. That is, even a slight change in the probe angle can cause a substantial speed change. To calculate the volume flow rate by this method, it is necessary to know the exact inner diameter of the blood vessel. Unless this inner diameter is measured by some other means, the accurate volume flow rate is not measured by this Doppler principle. Can not know. The linear velocity of blood in a blood vessel varies depending on its position. For example, the linear velocity near a blood vessel wall differs from the velocity near its center, so its flow velocity spectrum (shape of flow velocity distribution curve) differs for each blood vessel position. Because.

The flow rate measurement method using the transit time principle is different in the case where the propagation time of an ultrasonic wave over a certain distance propagates along the flow of a fluid and the case where it propagates against the flow. The time is based on the principle that the time is shorter than when the fluid is at rest and longer when the fluid is against the flow. In this transit time flow rate measurement method, since the flow rate in the blood vessel is directly measured, it is not necessary to strictly adjust the incident angle of the ultrasonic wave and to know the accurate blood vessel inner diameter. In addition, although there is an advantage that the measurement of the zero compensation value is not particularly required and that the measurement can be performed quickly, the propagation time difference proportional to the blood flow velocity is extremely small (picoseconds). ; About ^10-12 s), it was difficult to manufacture measuring instruments such as a probe and a processing device capable of accurately measuring the volume flow rate. Did not appear. Recently,
This type of device has been put to practical use for animal experiments and has been commercially available, but its accuracy and reproducibility are not yet sufficient.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional blood flow measuring apparatus, namely, zero compensation for each measurement data, fine adjustment of the probe measurement angle, and accurate blood vessel inner diameter. Ultra-transit-time blood flow that eliminates the need for simple investigations and solves all the problems of flow measurement devices that use the conventional transit time principle, and is excellent in speed, accuracy, reproducibility, and easy operation. It is to provide a measuring device.

Another object of the present invention is to obtain accurate blood flow and blood pressure at the same time, and to directly operate the obtained in-time measurement signal values to directly display the vascular impedance. It is an object of the present invention to provide an ultrasonic transit time type blood flow measuring device. Still another object of the present invention is to provide an ultrasonic transit time type blood flow measuring device which has an electronic element circuit such as an EEPROM in a probe and can calibrate detection data.

[0008]

According to the present invention, there is provided a blood flow measuring probe comprising an ultrasonic transmitting / receiving section, a blood vessel holding section with a slide-openable cover for inserting and removing a blood vessel, a connecting cord with a connector, and a handle. An ultrasonic processing device configured to receive an electrical signal from the perove via the connection cord to calculate a blood flow and calculate a blood flow, and an ultrasonic transit time type blood flow measurement device comprising at least a data display device; The ultrasonic transmission / reception unit has a band-shaped smooth, flat surface in contact with the blood vessel held by the blood vessel holding unit, and is arranged at an inner side thereof at an interval along the band-shaped plane, the inner diameter of the blood vessel or more. A pair of plate-shaped piezo elements capable of transmitting and receiving ultrasonic waves having a beam width of about 5 mm are built in, and the blood vessel holding section is arranged on the back side of the holding blood vessel in parallel with the plane of the ultrasonic transmitting / receiving section. And an ultrasonic reflector is provided at an intermediate point between the two piezo elements. First, an ultrasonic beam is emitted from one of the elements in an oblique direction toward the reflector, and the beam is transmitted to the plane and the blood vessel. To reach the reflector, is reflected by the reflector, passes through the blood vessel and the plane again, is received by the other piezo element, and then operates by reversing the transmission and reception of the two elements, There is provided an ultrasonic transit time type blood flow measuring device which measures a blood flow based on a phase difference between two received ultrasonic frequencies received by an operation.

The blood flow measuring device of the present invention is a flow measuring device utilizing the principle of ultrasonic transit time. Unlike the Doppler flow velocity measuring method utilizing the so-called Doppler shift effect, the blood flow measuring device directly measures the blood flow in the blood vessel. Is what you do.

The blood flow measuring apparatus of the present invention using the ultrasonic transit time method uses a piezo element as an ultrasonic transmitting / receiving element, and a wide ultrasonic beam sent from the entire surface of the element passes through the entire fluid cross section. Form a uniform ultrasonic field.

As apparent from the attached drawing (FIG. 3), first, an ultrasonic burst wave is transmitted from the upstream piezo element (132 in FIG. 3), and the blood vessel and the surrounding medium tissue , Reaches the reflector provided below the blood vessel, is reflected there, passes through the blood vessel again, and is received by the downstream piezo element (132 ′).

At this time, the propagation of the ultrasonic wave in the medium is accelerated by the blood flow, and the arrival time is earlier than when the blood flow is zero, and the arrival time is detected as a phase difference from the basic signal of the master oscillator.

In the next cycle, the transmitting and receiving functions are reversed to propagate the ultrasonic burst wave from the downstream side to the upstream side, but the propagation at this time is decelerated by the blood flow, contrary to the first cycle. And the arrival time is delayed. This received signal is similarly detected as a phase difference, and the blood flow is calculated and calculated because it is directly proportional to the phase difference between these two cycles.

In this case, in order to accurately detect the phase difference value between the two cycles, the ultrasonic beam width must be at least wider than the inner diameter of the blood vessel to be measured, and irradiation must be uniform at least within the range of the width. In the apparatus of the present invention, a plate-shaped piezo element is used as an ultrasonic transmission and reception element of the probe, and the front surface in contact with the blood vessel of the probe housing is formed in a smooth band-shaped plane, so that the irradiation ultrasonic wave is emitted. Undesirable scattering and dispersion are avoided, and a very accurate measurement of the phase difference value is enabled.

The blood flow velocity in a blood vessel differs depending on the position in the blood vessel. For example, in a normal blood flow, the blood flow velocity is the fastest in the central part of the blood vessel when viewed from the cross section of the blood vessel, near the wall. This apparatus detects a blood flow velocity corresponding to each position in these blood vessels as a phase difference value, and transmits this as a signal to the arithmetic processing unit. Then, the total flow rate in the blood vessel is calculated from these signals by a conversion operation circuit provided in the apparatus and displayed on the data display device.

Therefore, in the apparatus of the present invention, for example, the blood flow can be directly measured without particularly requiring a compensation operation such as a zero point compensation required in an apparatus using another method such as an electromagnetic flow measurement method. It has the advantage that it can be obtained quickly and accurately.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing basic components of the apparatus of the present invention. The apparatus of the present invention typically includes a probe (1) for measuring blood flow, and receives a signal from the probe to obtain a blood sample. An arithmetic processing unit (2) for calculating the flow rate, a data display unit (3), and a keyboard (4) for inputting operation conditions, detection data processing conditions, and display conditions such as data.
It is composed of

A code 11 is connected to the probe, and a connector 12 for connecting to an arithmetic processing unit is attached to a terminal of the code.

FIGS. 2a and 2b show the structure of the probe of the present invention.
As can be seen from reference, the probe (1) includes a probe housing (13) as an ultrasonic transmitting and receiving unit, a blood vessel holding unit (14) with a sliding cover, and an ultrasonic reflecting plate ( 142), a handle (15) attached to the housing for properly guiding and arranging the blood vessel holding portion and the housing of the probe at a location of a blood vessel whose flow rate is to be measured, and measuring data to the arithmetic processing device. The code (11) is transferred as a signal.

As shown in the figure, a flat and smooth frontal plane (131) in the form of a strip in contact with the blood vessel to be measured is formed on the probe housing (13) (ultrasonic transmission / reception unit). It is inserted between this plane and the reflector (142).

In the housing, two piezo elements (132, 13) are arranged at a distance along a band-shaped front plane.
2 ') is installed, as shown in FIG.
An ultrasonic beam is emitted from one of the elements toward a reflector located at the midpoint between the two piezo elements and on the back side of the measurement blood vessel. The irradiated beam passes through the front surface of the housing, passes through the blood vessel, reaches the reflector, is reflected there, passes through the blood vessel again, reaches the piezo element on the other side via the plane, and is received. . The electric signal received by the piezo element is transmitted to an arithmetic processing device and is subjected to arithmetic processing.

In the actual measurement, the transmission of the ultrasonic wave is repeated alternately from one of the elements to the other, as described above, and the phase difference between the two measurements is used as a parameter of the blood flow. Transmitted. The piezo element is a flat plate having a width of at least the inner diameter of the measured blood vessel,
Although not necessarily limited to this, it is preferable that at least the transmitting surface is formed of silicone.

It is necessary that the ultrasonic reflecting plate has an area large enough to appropriately reflect the irradiating beam and a flat reflecting plane, and a stainless steel surface polishing plate is preferably used as the material. Is done.

The slide type open / close cover (13) is inserted into the blood vessel holding portion (13) of the probe so that a measuring blood vessel can be inserted or removed between the front surface (131) of the housing and the reflecting surface (142). 141) is provided.

This cover of the present invention is a sliding type that does not require so-called screwing, so that it is not necessary to loosen the screws and move the cover. This has the advantage that the inconvenience of dropping or losing the probe into the blood flow measuring section of the probe is avoided.

In the apparatus of the present invention, it is preferable to use a probe having a size that matches the diameter of the blood vessel to be measured, in particular, the size of the probe, in particular, the size of the housing and the blood vessel holding portion. It is important to obtain, and it is therefore preferable to prepare various kinds of probes having different sizes. It is also important that the blood vessel to be measured is properly accommodated and arranged in the blood vessel holding portion so that the blood vessel to be measured is uniformly and well contacted along the front surface of the housing in order to obtain an accurate blood flow value. It is more preferable that a mechanism for judging the proper accommodation arrangement state and its indicator be provided.

Further, it is more preferable that the probe of the present invention is provided with an electronic circuit such as an EEPROM having an automatic calibration function of data, in which related parameters for flow rate calculation are stored, and thereby the accuracy of the measured value is improved. Can be further improved, and quickness can be further improved.

The arithmetic unit used in the present invention processes the measurement data signal transmitted from the probe, calculates the volume blood flow rate, and sets a display format (a table showing a numerical value / time relationship, Graph, etc.) on the display device according to the present invention. However, as the arithmetic processing unit of the arithmetic processing device of the present invention, except that the circuit mechanism for the arithmetic processing is incorporated in the form of, for example, a printed board board or the like. You can use a regular computer.

Typically, the same type as a commercially available personal computer may be used. Transit time calculation and data processing are performed by dedicated hardware compatible with a personal computer motherboard and dedicated software compatible with an operating system of a personal computer. The transit time probe is connected to a computer and transmits data signals to dedicated hardware.

Since the arithmetic processing unit of the present invention can be set so that signals from a plurality of probes can be processed simultaneously, a plurality of connection terminals, usually two to four connection terminals, may be provided.

The arithmetic processing device of the present invention can simultaneously perform arithmetic processing and display blood pressure, body temperature, electrocardiogram, respiratory rate, heart rate and the like measured and detected by a method known per se, in addition to the above-described blood flow. In, for example, a blood pressure and heart rate measurement mechanism is provided in parallel, the blood pressure value and the heart rate are simultaneously displayed together with the blood flow rate, and the impedance of the blood vessel is obtained in-time by using the obtained measurement signal values, for example, by Fourier transform, It is preferable to display this value. In such a case, the arithmetic unit is provided with a terminal group for inputting those data signals.

The blood flow impedance is an important parameter in a surgical operation such as a cardiac surgery, for example, and its value represents a dynamic aspect of blood flow in a blood vessel.
It differs from the blood flow resistance which is a static average value.

According to signal theory, a time-varying signal value is represented as an integrated sum of individual sinusoidal waves, each having a different amplitude, frequency and phase, the frequency of each wave always being an integral multiple of the fundamental frequency. Becomes That is, this value can be mathematically represented as the following Fourier series.

[0034]

(Equation 1) Here, P ₀ is the average blood pressure value, and t is the time

In the above equation, assuming that P (t) represents a time-varying dynamic pressure waveform at a certain position in a blood vessel, P (t) is, as can be seen from equation (1), the average pressure. It consists of a value term and an integrated sum term of sinusoidal waves. The first term of the term of the sum of sinusoidal waves is represented by P ₁ · sin (ω ₀ t−Ψ ₁ ) (2), where P ₁ is a frequency (ω ₀ ) ω ₀ = 2π · f ₀ ( 3) where f ₀ is the amplitude of the sine curve of the fundamental frequency.

In the medical field, as in the case of the present invention, this f ₀ always represents the heart rate. All frequencies of the signal are
Therefore, it becomes an integral multiple of the heart rate, and becomes a so-called harmonic frequency signal. This harmonic frequency is represented by ω _n = 2π · nf ₀ (4) n = 2,. The blood flow value (Q (t)) is similarly represented,

(Equation 2) Here, q ₀ is the average volume flow value.

Therefore, the impedance value (Z (t))
Is the ratio of P (t) to Q (t), that is,

(Equation 3) Is represented by As can be seen from the equation (6), the impedance value includes the average resistance value R = p ₀ / q ₀ and the time-varying signal value, and more completely represents the flow state of the blood flow in the blood vessel. It is.

As can be clearly understood from the above description and the equation of Z (t), the calculation of the blood flow impedance value requires accurate measurement of the blood flow value and the blood pressure value, which change every moment due to pulsation. is there. The blood flow impedance is obtained after the time-varying P (t) and Q (t) are calculated and converted by the rapid Fourier transform method, and are expressed as component values at predetermined time intervals.

Since the blood flow measuring device of the present invention is based on the transit time method, it is possible to display a time-varying blood flow waveform very accurately.
Therefore, by combining known blood pressure measurement methods, it is possible to obtain impedance values significantly more accurately and quickly than in the conventional case.

FIG. 4 is a schematic diagram showing an example of a screen displaying a blood flow diagram, a blood pressure diagram and an impedance value obtained by the blood flow measuring apparatus according to this embodiment of the present invention.

Further, in the blood flow measuring device of the present invention, for example, a Doppler shift type probe utilizing the Doppler principle is connected, and the blood flow value measured by the transit time probe and the blood flow rate measured by the Doppler shift probe are measured. Can be displayed simultaneously.

The data processed and calculated by the arithmetic processing unit of the present invention is displayed on a screen by a display (CRT) or the like in principle. The data can be printed out from a printer and displayed as a document, or a fixed disk or a floppy disk can be displayed. It is also optional to fill out and save on a disk or the like.

As the display device, output device, data storage device, and keyboard for inputting control conditions such as measurement conditions, display conditions, and output conditions, those known per se can be used.

The blood flow measuring device of the present invention has a very small flow rate accuracy of about ± 2% as a relative error and an absolute error within ± 10%, which is extremely superior to the conventional product.

[0045]

EXAMPLE Blood blood flow was measured at 356 places of blood vessels of 10 pigs at an ultrasonic frequency of 2.5 MHz using a probe of 5 mm size (measurement flow rate range 0 to 580).
ml / min). At the same time as the above measurement, the blood flow of the same blood vessel is received by the container with the correction scale, and the flow rate is measured. Calculated. The average value of the errors expressed as the number of absolute values at 356 points was 4.7%.

[0046]

The blood flow measuring device of the present invention uses the transit time method and measures the blood flow using the probe having the above-mentioned specific structure, and thus is compared with the conventional electromagnetic flow measuring device. It does not require a high level of skill in the measurement operation, does not require zero point compensation for each data required for this type of apparatus, and is extremely excellent in accuracy. Furthermore, unlike the case of the electromagnetic flow measurement method, the measurement value is not affected by the red blood cell concentration (hematocrit) in the blood. Furthermore, unlike the Doppler shift velocimeter, it is not only possible to perform quick measurement without requiring strict fine adjustment of the probe angle, but also it is not necessary to know an accurate inner diameter of a blood vessel by a preliminary investigation. In addition, compared to the transit-time type blood flow meter that has been used for conventional animal experiments, etc., it shows extremely excellent measurement value accuracy and reproducibility, and is excellent in operability. It exhibits excellent performance when applied to surgery, for example, femoral bypass graft surgery, cardiac surgery, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing components of an ultrasonic transit time type blood flow measuring instrument of the present invention.

FIG. 2 is a diagram showing a configuration of a probe in the apparatus of the present invention.

FIG. 3 is a schematic diagram for explaining a measurement principle of the apparatus of the present invention.

FIG. 4 is a schematic diagram showing an example of a blood flow, blood pressure, and impedance value diagram obtained by a blood flow measurement device of the present invention provided with an impedance value measurement calculation mechanism.

[Explanation of symbols]

 Reference Signs List 1 probe 2 arithmetic processing unit 3 data display device 4 keyboard 11 code 12 connector 13 probe housing (ultrasonic transmission / reception unit) 14 blood vessel holding unit 15 handle 100 blood vessel 131 front plane 132, 132 'piezo element 141 slide type cover 142 reflector

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) A61B 8/06

Claims (4)

(57) [Claims] 1. A blood flow measuring probe comprising: an ultrasonic transmitting / receiving unit; a blood vessel holding unit with a slide-openable cover for inserting and removing a blood vessel; a connection cord with a connector; and a handle;
An ultrasonic transit time type blood flow measuring device comprising at least an arithmetic processing device that receives an electric signal from the probe via a connection cord to calculate a blood flow, and a data display device, The sound wave transmission and reception unit has a band-shaped smooth, flat plane in contact with the blood vessel held by the blood vessel holding unit,
And a pair of plate-shaped piezo elements capable of transmitting and receiving ultrasonic waves having a beam width equal to or larger than the inner diameter of the blood vessel, which are arranged at intervals along the band-shaped plane on the inner side thereof, are built-in. On the back side of the blood vessel, an ultrasonic reflector is provided in parallel with the plane of the ultrasonic transmission / reception unit and at an intermediate point between the two piezo elements.First, an oblique direction is reflected from one of the piezo elements. Emits an ultrasonic beam towards the plate, the beam passes through the plane and the blood vessels, reaches the reflector, is reflected by the reflector, passes through the blood vessels and the plane again, is received by the other piezo element, and then An ultrasonic transit time blood flow measuring device, wherein the operation is performed by reversing the transmission and reception of the two elements, and measuring the blood flow based on the phase difference between the two received ultrasonic frequencies received by the two operations. . 2. The apparatus according to claim 1, further comprising a blood pressure measuring mechanism.
The ultrasonic transit time type blood flow measuring device as described in the above. 3. The arithmetic processing device according to claim 2, further comprising an arithmetic mechanism for calculating an impedance value of a blood vessel from the obtained blood flow measurement value and blood pressure measurement value, and capable of displaying an impedance curve. Ultrasonic transit time type blood flow measurement device. 4. The ultrasonic transit time blood flow measuring device according to claim 1, wherein said probe is provided with an electronic circuit capable of automatically calibrating the detected data.