JP2018105879A - Fluid evaluation device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid evaluation device that suitably calculates at least one of a flow rate and flow velocity of fluid while taking the concentration of the fluid into account.SOLUTION: A fluid evaluation device 1 comprises: irradiation means 11 for irradiating a measurement object 100 inside of which fluid is flowing with a laser beam LB; light-receiving means 12 for receiving the laser beam radiated to the measurement object and generating a light-receiving signal; and calculation means for calculating flow velocity of the fluid. The calculation means calculates flow velocity so that, under a situation where frequency change of the light-receiving signal caused by Doppler shift of the laser beam radiated to the measurement object are the same, flow velocity that is calculated when the concentration of the fluid is low is smaller than flow velocity that is calculated when the concentration is high.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technical field of a fluid evaluation apparatus and method for evaluating a fluid by detecting at least one of a flow rate and a flow velocity of the fluid such as a blood flow.

  As this type of fluid evaluation apparatus, for example, there is a laser blood flow meter that calculates a blood flow (see, for example, Patent Document 1). This laser blood flow meter calculates the blood flow rate of the living body based on the change in the wavelength of the laser light caused by the Doppler shift that occurs when the laser light applied to the living body is scattered. More specifically, when a living body is irradiated with laser light, scattered light scattered by a blood flow in the blood vessel of the living body (i.e., movement of blood cells that are scatterers) and other fixed tissues (particularly, Scattered light is generated by skin tissue, non-moving tissue such as a transparent tube forming a window or a flow path). The frequency of the scattered light scattered by the scatterer blood cell is changed by the laser Doppler action corresponding to the moving speed of the scatterer blood cell compared to the frequency of the scattered light scattered by other fixed tissues. Yes. Therefore, by receiving these two types of scattered light, a signal component corresponding to a so-called frequency difference signal resulting from the mutual interference between the two types of scattered light can be obtained. By analyzing this signal component (for example, a power spectrum is calculated), the blood flow rate of the living body is calculated.

  Other prior art documents related to the present invention include Patent Document 2 and Patent Document 3. Patent Document 2 discloses a fluid evaluation apparatus that calculates blood flow velocity and blood concentration indirectly indicating blood flow volume using light emitted from the same light source. Patent Document 3 discloses a fluid evaluation apparatus that calibrates a blood flow detected using an ultrasonic Doppler signal based on a blood flow detected using a thermodilution method.

Japanese Patent No. 3313841 JP-A-62-212669 Japanese Patent Publication No. 7-16490

  The fluid evaluation apparatus disclosed in Patent Document 1 mainly calculates the blood flow volume of blood flowing in a blood vessel of a living body. In this case, the concentration of blood in the blood vessel (for example, the concentration of blood cells such as red blood cells) hardly fluctuates. On the other hand, the fluid evaluation apparatus may detect not only the blood flowing in the blood vessel but also the blood flow rate of the blood flowing in a conduit outside the living body (for example, a transparent tube) used during artificial dialysis.

  However, the concentration of blood flowing through a conduit outside the living body used during artificial dialysis can vary greatly due to the nature of artificial dialysis. As described above, when the blood concentration fluctuates, the fluid evaluation apparatus disclosed in Patent Document 1 cannot calculate the blood flow volume suitably (in other words, with high accuracy). have. This is because, particularly when the blood concentration is relatively low, noise due to the parasitic capacitance of the input terminal of the amplifier that amplifies the received light signal, which is the light reception result of the scattered light of the laser light irradiated to the conduit. This is because the influence becomes relatively large.

  Note that the above-described technical problem can occur not only when blood flow is detected, but also when the flow rate of an arbitrary fluid flowing through an arbitrary pipeline (or a flow rate indirectly indicating the flow rate) is detected.

  The present invention has been made in view of the above problems, for example, and provides a fluid evaluation apparatus and method capable of suitably calculating at least one of the flow rate and flow velocity of a fluid while considering the concentration of the fluid. Is an issue.

  A first fluid evaluation apparatus for solving the above problem includes an irradiation unit capable of irradiating at least a laser beam to a measurement target in which a fluid flows, and the laser beam irradiated to the measurement target. A light receiving means for generating a light reception signal by converting the received laser light into an electrical signal, and a calculation means for calculating a flow rate of the fluid, wherein the calculation means irradiates the object to be measured. The flow rate calculated when the concentration of the fluid is low is calculated when the concentration is high in a situation where the frequency change of the light reception signal caused by the Doppler shift of the laser beam is the same. The flow rate is calculated so as to be smaller than the flow rate.

  A second fluid evaluation apparatus for solving the above-described problems includes an irradiation unit capable of irradiating at least laser light to a measurement target in which a fluid flows, and the laser light irradiated to the measurement target. A light receiving means for generating a light reception signal by converting the received laser light into an electrical signal, and a calculation means for calculating the flow velocity of the fluid, wherein the calculation means irradiates the object to be measured. The flow rate calculated when the concentration of the fluid is low in a situation where the frequency change of the light reception signal caused by the Doppler shift of the laser beam is the same is calculated when the concentration is high The flow rate is calculated so as to be smaller than the flow rate.

  A third fluid evaluation apparatus for solving the above-described problems includes an irradiating means capable of irradiating at least a laser beam to a measurement target in which a fluid flows, and the laser beam irradiated to the measurement target. A light receiving means for generating a light reception signal by converting the received laser light into an electrical signal, and a calculation means for calculating a flow rate of the fluid, wherein the calculation means irradiates the object to be measured. The flow rate calculated when the fluid concentration is the first concentration under the situation where the frequency change of the light reception signal due to the Doppler shift of the laser beam is the same, the fluid concentration is The flow rate is calculated so as to be smaller than the flow rate calculated when the second concentration is higher than the first concentration.

  A fourth fluid evaluation apparatus for solving the above-described problems includes an irradiating means capable of irradiating at least a laser beam to a measurement target in which a fluid flows, and the laser beam irradiated to the measurement target. A light receiving means for generating a light reception signal by converting the received laser light into an electrical signal, and a calculation means for calculating the flow velocity of the fluid, wherein the calculation means irradiates the object to be measured. The flow rate calculated when the concentration of the fluid is the first concentration under the situation where the frequency change of the received light signal caused by the Doppler shift of the laser beam is the same, the concentration of the fluid is The flow rate is calculated so as to be smaller than the flow rate calculated when the second concentration is higher than the first concentration.

It is a block diagram which shows the structure of the blood flow rate calculation apparatus of 1st Example. It is a flowchart which shows the flow of operation | movement of the blood flow rate calculation apparatus of 1st Example. The correlation between the light intensity signal and the blood flow concentration when the light receiving element receives the forward scattered light of the laser light, and the light intensity signal and the blood flow concentration when the light receiving element receives the back scattered light of the laser light. It is a graph which shows the correlation between. Sample of beat signal when blood flow rate is relatively slow and power spectrum (that is, frequency-power characteristics) obtained by performing FFT on beat signal sample value when blood flow rate is relatively fast It is a graph which shows the power spectrum obtained by performing FFT with respect to a value. When the blood flow concentration is relatively high, the FFT is performed on the beat signal sample value when the power spectrum obtained by performing the FFT on the beat signal sample value and the blood flow concentration is relatively low. It is a graph which shows both each ideal value and actual value of the power spectrum obtained by (1). It is a graph which shows the correlation between the flow velocity of blood and the average frequency of a power spectrum according to blood flow concentration. It is a graph which shows the relationship between each of the inclination correction value and intercept correction value applied when calculating the blood flow velocity from the average frequency of a power spectrum, and blood flow concentration. It is a block diagram which shows the structure of the blood flow rate calculation apparatus of 2nd Example. It is a block diagram which shows the structure of the blood flow rate calculation apparatus of 3rd Example. It is a block diagram which shows the structure of the blood flow rate calculation apparatus of 4th Example. It is a block diagram which shows the structure of the specific example of the light receiving element and amplifier with which the blood flow rate calculation apparatus of 4th Example is equipped with the blood flow rate calculation apparatus of 1st Example.

  Hereinafter, embodiments of a fluid evaluation apparatus and method will be described in order as modes for carrying out the invention.

(Embodiment of fluid evaluation apparatus)
<1>
The fluid evaluation apparatus according to the present embodiment includes an irradiating unit capable of irradiating at least a laser beam to a measurement target in which a fluid flows, and a light receiving unit capable of receiving at least the laser beam irradiated to the measurement target. Means, a first calculation means for calculating the concentration of the fluid from a first received light signal based on the signal intensity of the received light signal received by the light receiving means, and (i) the laser beam irradiated to the measurement target A second light receiving signal based on a frequency change of the light receiving signal caused by a Doppler shift, and (ii) a second flow for detecting at least one of the flow rate of the fluid and the flow velocity of the fluid from the concentration calculated by the first calculation means. Calculating means.

  According to the fluid evaluation apparatus of the present embodiment, the irradiation unit irradiates the measurement target with laser light. A fluid flows inside the object to be measured. The laser light is preferably applied to the fluid. Examples of the measurement target and the fluid include living bodies such as humans and animals and blood. Alternatively, as another example of the measurement target and the fluid, an artificial conduit through which blood flows and blood can be cited. Alternatively, as another example of the object to be measured and the fluid, a tube having a light transmissive window and a transparent tube, and a fluid flowing in the tube or the tube (for example, ink, oil, sewage, seasoning, etc. A fluid containing at least a scatterer that scatters light as a constituent element).

  The light receiving unit receives the laser beam irradiated to the measurement target by the irradiation unit. Specifically, for example, the light receiving unit receives laser light (so-called scattered light) scattered by the measurement target. At this time, the light receiving means may receive laser light transmitted through the object to be measured (so-called forward scattered light corresponding to transmitted light), or laser light reflected by the object to be measured (so-called reflected light). May be received. As a result, a light receiving signal corresponding to the received laser light (particularly, scattered light of the laser light) is output from the light receiving means.

  The first calculation means uses the first received light signal (in other words, the signal component indicating the signal intensity of the received light signal) based on the signal intensity of the received light signal (for example, the average signal intensity or the signal intensity of the DC component included in the received signal). The fluid concentration is calculated from the corresponding first light receiving signal). For example, when the light receiving means receives laser light (that is, forward scattered light) that has passed through the object to be measured, the higher the concentration of the fluid (that is, the scatterer that prevents the transmission of the laser light, etc.) The more it is included, the smaller the signal intensity of the received light signal (for example, the amplitude value or peak value of the first received light signal). Alternatively, for example, when the light receiving means receives laser light (that is, backscattered light) reflected by the object to be measured, the higher the concentration of the fluid (that is, the scatterer that reflects the laser light). The more it is contained in the fluid), the greater the signal intensity of the received light signal. The first calculation means calculates the density using the relationship between the signal intensity and the density of the received light signal.

  Since the concentration is calculated using the relationship between the signal intensity and the concentration of such a light reception signal, the “fluid concentration” in this embodiment is the scatterer included in the fluid. Corresponds to concentration.

  The second calculation means is a second light reception signal (in other words, the frequency of the light reception signal) based on the frequency change of the light reception signal caused by the Doppler shift of the laser light (particularly, the scattered light of the laser light) irradiated to the measurement target. At least one of the flow rate of the fluid and the flow rate of the fluid is calculated from the second received light signal corresponding to the signal component including the change. Specifically, for example, when laser light is irradiated on the measurement target, scattered light is generated due to the flow of fluid inside the measurement target. This scattered light includes scattered light scattered by scatterers contained in the fluid (especially moving scatterers) and other fixed tissues (especially skin tissues, transparent tubes forming windows and channels). And scattered light scattered by a non-moving tissue). The frequency of the scattered light scattered by the moving scatterer is changed by the laser Doppler action corresponding to the flow velocity of the fluid, compared with the frequency of the scattered light scattered by other fixed tissues. Due to the mutual interference between these two types of scattered light, the received light signal includes a signal component corresponding to a so-called frequency difference signal. By analyzing this signal component, at least one of the flow rate and the flow velocity is calculated.

  In the present embodiment, in particular, the second calculation unit is configured to determine the flow rate and the flow rate based on the concentration calculated by the first calculation unit in addition to the second light reception signal based on the frequency change of the light reception signal caused by the Doppler shift of the laser light. At least one of the flow rates is calculated. For example, conventionally, the second calculation means calculates the same flow rate (or the same flow rate) when the frequency change of the received light signal is the same. However, in the present embodiment, the second calculation means may calculate different flow rates (or different flow velocities) even when the frequency changes of the received light signals are the same, and when the concentrations are different. For example, assuming that the second calculation means calculates the first flow rate (or the first flow velocity) when the frequency change is a predetermined mode and the concentration is the first concentration, the frequency change is a predetermined mode. The second flow rate is different from the first flow rate (or the second flow rate is different from the first flow rate). 2) may be calculated.

  If at least one of the flow rate and the flow velocity is calculated without being based on the concentration calculated by the first calculation means, at least one of the flow rate and the flow velocity may not be calculated appropriately. This is because when the concentration of the fluid is relatively low, the number of scatterers that move in the fluid per unit volume is small, and therefore, in the received light signal due to the Doppler shift of the laser light caused by the movement of the scatterers. The power of the optical beat signal included in the signal is reduced. On the other hand, since the noise power caused by the parasitic capacitance of the input terminal of the amplifier that amplifies the received light signal, which is the result of receiving the scattered light of the laser light irradiated to the object to be measured, does not change, the influence of noise is relatively large. Because it becomes. In other words, when the fluid concentration is relatively low, it is strongly influenced by noise caused by the parasitic capacitance of the input terminal of the amplifier, and the light receiving result that is the result of receiving the scattered light of the laser light irradiated to the measurement target. This is because the frequency change of the signal may be different from the frequency change that should appear originally. Even in the case where the concentration of fluid is relatively high, similar technical problems may occur accordingly. Therefore, depending on the concentration of the fluid, the frequency change of the received light signal, which is the result of receiving the scattered light of the laser light irradiated to the object to be measured, may change unintentionally from the frequency change that should originally appear. . However, since the fluid evaluation apparatus according to the present embodiment refers to the concentration of the fluid so as to eliminate the influence of such noise, it is possible to suitably calculate at least one of the flow rate and the flow velocity.

  As described above, the fluid evaluation apparatus according to the present embodiment can calculate (in other words, with high accuracy) at least one of the flow rate of the fluid and the flow velocity of the fluid in consideration of the concentration of the fluid. In particular, in the fluid evaluation apparatus of this embodiment, the blood (that is, the concentration (for example, the concentration of red blood cells) flowing through a conduit (for example, a transparent tube) external to the living body used during artificial dialysis varies relatively. Even when blood that is easy to do is an example of a fluid, at least one of the flow rate and flow velocity of the fluid (that is, blood) can be suitably calculated. Of course, the fluid evaluation apparatus according to the present embodiment allows the flow rate of the fluid (that is, blood) even in the case where blood flowing in the blood vessel of the living body (that is, blood whose concentration is relatively difficult to change) is an example of the fluid. And at least one of the flow velocity can be suitably calculated.

  Note that, under the condition that the flow paths through which the fluid flows are the same, the flow rate of the fluid and the flow velocity of the fluid have a positive correlation. That is, if the flow rate of the fluid flowing through a certain flow path increases, the flow rate of the fluid flowing through the flow path increases, whereas if the flow rate of the fluid flowing through the certain flow path decreases, the flow rate of the fluid flowing through the flow path. Has a correlation of slowing down. Therefore, it can be said that the calculation of the flow rate and the calculation of the flow velocity are substantially the same. That is, the calculation of the flow velocity is substantially equivalent to the indirect calculation of the flow rate, and the calculation of the flow rate is substantially equivalent to the indirect calculation of the flow rate.

<2>
In another aspect of the fluid evaluation apparatus of the present embodiment, the irradiating means includes: (i) a first irradiating means that irradiates the measurement target with measurement light that is a type of light different from the laser light; (ii) second irradiating means for irradiating the object to be measured with the laser light, and the light receiving means (i) receives the measurement light irradiated to the object to be measured to receive the first light. (Ii) acquiring the second received light signal by receiving the laser beam irradiated to the measurement target, and the first calculating means, from the first received light signal, The concentration is calculated, and the second calculation means calculates at least one of the flow rate and the flow velocity from (i) the second received light signal and (ii) the concentration calculated by the first calculation means.

  According to this aspect, the irradiation unit is separated into the first irradiation unit mainly used for calculating the concentration and the second irradiation unit mainly used for calculating at least one of the flow rate and the flow velocity. Therefore, the first irradiating means does not depend on calculation of at least one of the flow rate and the flow velocity, and the measurement light suitable for calculating the concentration (for example, 805 nm which does not depend on the oxygen saturation in the bloodstream which is an example of the fluid). Of light). On the other hand, the second irradiation means is a laser beam suitable for calculation of at least one of flow rate and flow velocity without much consideration of concentration calculation (for example, a semiconductor laser having high monochromaticity and coherence and widely distributed) 780 nm light that can be emitted from the light source).

<3>
In another aspect of the fluid evaluation apparatus of the present embodiment, the light receiving means includes: (i) a first light receiving means for acquiring the first light receiving signal by receiving the laser light irradiated on the measurement target; (Ii) second light receiving means for obtaining the second light receiving signal by receiving the laser light irradiated to the measurement object, wherein the first calculating means comprises the first light receiving signal. And the second calculating means calculates at least one of the flow rate and the flow velocity from (i) the second received light signal and (ii) the concentration calculated by the first calculating means. .

  According to this aspect, the light receiving means is separated into the first light receiving means mainly used for calculating the concentration and the second light receiving means mainly used for calculating at least one of the flow rate and the flow velocity.

<4>
In another aspect of the fluid evaluation apparatus of the present embodiment, the irradiation unit includes the first irradiation unit and the second irradiation unit as described above. Furthermore, the light receiving means includes (i) first light receiving means for acquiring the first light receiving signal by receiving the measurement light irradiated to the measurement target; and (ii) irradiating the measurement target. Second light receiving means for obtaining the second light receiving signal by receiving the laser light, wherein the first calculating means calculates the concentration from the first light receiving signal, and 2 calculating means calculates at least one of the flow rate and the flow velocity from (i) the second received light signal and (ii) the concentration calculated by the first calculating means.

  According to this aspect, the irradiation unit is separated into the first irradiation unit mainly used for calculating the concentration and the second irradiation unit mainly used for calculating at least one of the flow rate and the flow velocity. Further, the light receiving means is separated into a first light receiving means mainly used for calculating the concentration and a second light receiving means mainly used for calculating at least one of the flow rate and the flow velocity.

<5>
In another aspect of the fluid evaluation apparatus including the first light receiving means and the second light receiving means as described above, the light receiving area of the first light receiving means is larger than the light receiving area of the second light receiving means.

According to this aspect, the light receiving area of the first light receiving means used mainly for calculating the density is relatively large. For this reason, it is possible to relatively improve the S / N ratio of the first light reception signal used for detecting the density. On the other hand, the light receiving area of the second light receiving means used mainly for calculating at least one of the flow rate and the flow velocity is relatively small. For this reason, the influence of amplifier noise (more specifically, parasitic capacitance of the input terminal of the amplifier that contributes to the generation of the noise) that contributes to lowering the calculation accuracy of at least one of the flow rate and the flow velocity is relatively measured. Can be reduced. )
The first light receiving means and the second light receiving means preferably receive at least one of the laser light and the measurement light so that the light receiving area is relatively small between the second light receiving means and the irradiation means. The distance between them may be shorter than the distance between the first light receiving means and the irradiating means in which the light receiving area is relatively large. In other words, the second light receiving means having a relatively small light receiving area is preferably as close to the irradiation means as possible.

<6>
In another aspect of the fluid evaluation apparatus of the present embodiment, the second calculation means is based on correlation information that defines a correlation between the frequency change and at least one of the flow rate and the flow velocity for each concentration. At least one of the flow rate and the flow rate is calculated.

  According to this aspect, the second calculation means can suitably calculate at least one of the flow rate and the flow velocity relatively easily based on the correlation information. Specifically, the second calculation means can relatively easily calculate at least one of the flow rate and the flow velocity from the frequency change by referring to the correlation according to the concentration calculated by the first calculation means.

<7>
In another aspect of the fluid evaluation apparatus of the present embodiment, the second calculation means calculates the correlation between the average frequency obtained by analyzing the frequency change and at least one of the flow rate and the flow velocity as the concentration. Based on the correlation information specified separately, at least one of the flow rate and the flow velocity is calculated.

  According to this aspect, the second calculation means can suitably calculate at least one of the flow rate and the flow velocity relatively easily based on the correlation information. Specifically, the second calculation means compares at least one of the flow rate and the flow velocity from the average frequency obtained by analyzing the frequency change by referring to the correlation according to the concentration calculated by the first calculation means. Can be calculated easily.

  Note that the second calculation means is based on the correlation information that defines the correlation between an arbitrary parameter obtained by analyzing the frequency change and at least one of the flow rate and the flow rate for each concentration, and at least one of the flow rate and the flow rate. May be calculated.

<8>
As described above, in the aspect of the fluid evaluation apparatus that calculates at least one of the flow rate and the flow rate based on the correlation information that defines the correlation between the average frequency and at least one of the flow rate and the flow rate for each concentration, the correlation information includes In a situation where the average frequency is the same, at least one of the flow rate and the flow rate calculated when the concentration is relatively low is equal to the flow rate and the flow rate calculated when the concentration is relatively high. A correlation between the average frequency and at least one of the flow rate and the flow rate is defined for each concentration so as to be smaller than at least one.

  According to this aspect, the second calculation means can suitably calculate at least one of the flow rate and the flow velocity relatively easily based on such correlation information. Specifically, the case where the average frequency obtained by analyzing the frequency change is the first frequency will be described as an example. In this case, when the concentration is the first concentration that is relatively low, the second calculation means calculates at least one of the first flow rate that is a relatively small flow rate and the first flow rate that is a relatively small flow rate. To do. On the other hand, when the concentration is a second concentration that is relatively high, the second calculation means calculates at least one of a second flow rate that is a relatively large flow rate and a second flow rate that is a relatively large flow rate. .

  The correlation information of this aspect is such that the average frequency when the concentration is relatively low is higher than the average frequency when the concentration is relatively high in a situation where at least one of the flow rate and the flow velocity is the same. In addition, it can be said that the correlation between the average frequency and at least one of the flow rate and the flow velocity is defined for each concentration.

  In addition, as described above, the second calculation means calculates the flow rate based on the correlation information that defines the correlation between an arbitrary parameter obtained by analyzing the frequency change and at least one of the flow rate and the flow velocity for each concentration. And / or at least one of the flow rates may be calculated. In this case, the correlation information indicates that at least one of the flow rate and the flow rate calculated when the concentration is relatively low in a situation where arbitrary parameters obtained by analyzing the frequency change are the same, the concentration is relative. The correlation between an arbitrary parameter and at least one of the flow rate and the flow rate may be defined for each concentration so as to be smaller than at least one of the flow rate and the flow rate calculated when the flow rate is high.

<9>
In another aspect of the fluid evaluation apparatus of the present embodiment, the cycle in which the second calculation unit calculates at least one of the flow rate and the flow velocity of the fluid is shorter than the cycle in which the first calculation unit calculates the concentration.

  According to this aspect, the first calculation means has a relatively long period based on the signal intensity of the received light signal having a relatively low frequency (in other words, the signal intensity that is a signal component having a relatively low frequency). (In other words, with a relatively low frequency), the concentration can be calculated. Further, the second calculating means is based on a frequency change of the received light signal having a relatively high frequency (in other words, a frequency change that is a signal component of a relatively high frequency) with a relatively short period (in other words, At a relatively high frequency) and / or at least one of flow rate and flow rate can be calculated.

<10>
In another aspect of the fluid evaluation apparatus of this embodiment, the fluid is a blood flow of a living body as the measurement target.

  According to this aspect, the first calculation means can calculate the concentration of blood (for example, the concentration of red blood cells that are scatterers). Further, the second calculation means can calculate at least one of a blood flow rate (that is, a blood flow rate) and a blood flow velocity.

(Embodiment of fluid evaluation method)
<11>
The fluid evaluation method according to the present embodiment includes an irradiation unit capable of irradiating at least a laser beam to a measurement target in which a fluid flows therein, and a light reception capable of receiving at least the laser beam irradiated to the measurement target. A fluid evaluation method in a fluid evaluation apparatus comprising: a first calculation step of calculating a concentration of the fluid from a first light reception signal based on a signal intensity of a light reception signal received by the light reception means; (i) From the second light reception signal based on the frequency change of the light reception signal caused by the Doppler shift of the laser light irradiated to the measurement target, and (ii) the flow rate of the fluid and the concentration calculated by the first calculation step A second calculation step of calculating at least one of the flow rates of the fluid.

  According to the fluid evaluation method of this embodiment, the various effects which the fluid evaluation apparatus of this embodiment mentioned above enjoys can be enjoyed suitably.

  Incidentally, in response to various aspects adopted by the fluid evaluation apparatus of this embodiment, the fluid evaluation method of this embodiment may adopt various aspects.

  Such an operation and other advantages of the present embodiment will be clarified from examples described below.

  As described above, the fluid evaluation apparatus according to the present embodiment includes the irradiation unit, the light receiving unit, the first calculation unit, and the second calculation unit. The fluid evaluation method of the present embodiment includes a first calculation step and a second calculation step. Accordingly, at least one of the flow rate of the fluid and the flow rate of the fluid is calculated suitably (in other words, with high accuracy) while considering the concentration of the fluid.

  Hereinafter, embodiments of the fluid evaluation apparatus will be described with reference to the drawings. In the following, description will be given of an example in which the fluid evaluation device is applied to a blood flow rate calculation device that detects the flow rate of blood flowing in the tube 100 constituting the blood flow circuit of the artificial dialysis device (that is, blood flow rate). . However, the fluid evaluation apparatus is an arbitrary device that detects the flow rate of blood flowing in the blood vessel of a living body (that is, the blood flow rate) or the flow rate of any fluid other than blood (for example, ink, oil, sewage, seasoning, etc.). The present invention may be applied to a flow rate detection device.

(1) First Example First , the blood flow rate calculation device 1 of the first example will be described with reference to FIGS.

(1-1) Configuration of Blood Flow Calculation Device First, the configuration of the blood flow calculation device 1 of the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a blood flow rate calculation device 1 according to the first embodiment.

  As shown in FIG. 1, the blood flow rate calculation device 1 according to the first embodiment includes a laser element 11, a light receiving element 12, an amplifier 13, and an arithmetic circuit 14.

  The laser element 11 constitutes a specific example of “irradiation means” and irradiates the tube 100 with the laser beam LB. At this time, the laser element 11 preferably irradiates the flow path in the tube 100 (that is, the flow path through which blood flows) with the laser beam LB.

  The light receiving element 12 constitutes a specific example of “light receiving means” and receives scattered light of the laser light LB irradiated to the tube 100. The scattered light received by the light receiving element 12 includes scattered light scattered by blood flowing in the tube 100 (particularly, blood cells that are moving scatterers contained in the blood) and stationary tissue ( For example, scattered light scattered by the tube 100 itself) is included. The light receiving element 12 generates a received light signal obtained by converting the received scattered light into an electrical signal.

  The amplifier 13 converts the received light signal, which is a current signal output from the light receiving element 12, into a voltage signal, and then amplifies it.

  The arithmetic circuit 14 is based on the output of the amplifier 13 (that is, the light reception signal corresponding to the scattered light received by the light receiving element 12), and the blood flow rate (that is, the blood flow rate) Q and the blood concentration ( Blood flow concentration) N is calculated. In order to calculate the blood flow rate Q and the blood flow concentration N, the calculation circuit 14 includes an LPF (Low Pass Filter) 141, an A / D converter 142, a calculator 143, an HPF (High Pass Filter) 144, A / D converter 145 and calculator 146 are provided.

  The LPF 141 cuts signal components in frequency bands other than the low-frequency signal component among the signal components included in the output of the amplifier 13 (that is, the light-receiving signal corresponding to the scattered light received by the light-receiving element 12). As a result, the LPF 141 outputs a light intensity signal corresponding to a low-frequency signal component among the signal components included in the output of the amplifier 13 to the A / D converter 142. The light intensity signal is a signal that directly or indirectly indicates the light intensity (for example, average light intensity) of scattered light received by the light receiving element 12.

  The light intensity signal is often a signal component having a frequency of 1 kHz or less, for example. Therefore, it is preferable that the LPF 141 has a cutoff frequency capable of cutting a signal component having a frequency (for example, 1 kHz or more) higher than that of the light intensity signal while passing at least the light intensity signal.

  The A / D converter 142 performs A / D conversion processing (that is, quantization processing) on the light intensity signal output from the LPF 141. As a result, the A / D converter 142 calculates the sample value (that is, the quantized light intensity signal) of the light intensity signal included in the voltage signal corresponding to the scattered light received by the light receiving element 12 as the arithmetic circuit 143. Output to.

  The arithmetic circuit 143 constitutes a specific example of “first calculation means”, and the output of the A / D converter 142 (that is, the light included in the voltage signal corresponding to the scattered light received by the light receiving element 12). Based on the sample value of the intensity signal, the blood flow concentration N is calculated.

  The HPF 144 cuts signal components in frequency bands other than the high-frequency signal component among the signal components included in the output of the amplifier 13 (that is, the received light signal corresponding to the scattered light received by the light receiving element 12). As a result, the HPF 144 outputs a beat signal corresponding to the high frequency signal component of the signal components included in the output of the amplifier 13 to the A / D converter 145. The beat signal extracted by the HPF 144 is, for example, a beat signal generated by mutual interference between scattered light scattered by blood cells that are moving scatterers and scattered light scattered by a stationary tissue.

  The beat signal is often a signal component having a frequency of 1 kHz or more, for example. Accordingly, it is preferable that the HPF 144 has a cut-off frequency capable of cutting a signal component having a frequency (for example, 1 kHz or less) lower than that of the beat signal while passing at least the beat signal. However, instead of the HPF 144, a BPF (Band capable of cutting both a signal component having a frequency higher than the frequency of the beat signal and a signal component having a frequency lower than the frequency of the beat signal while passing at least the beat signal. Pass Filter) may be used.

  The A / D converter 145 performs A / D conversion processing (that is, quantization processing) on the beat signal output from the HPF 144. As a result, the A / D converter 145 outputs the sample value of the beat signal (that is, the quantized beat signal) included in the voltage signal corresponding to the scattered light received by the light receiving element 12 to the arithmetic circuit 146. To do.

  The arithmetic circuit 146 constitutes a specific example of “second calculation means”, and the output of the A / D converter 145 (that is, the beat included in the voltage signal corresponding to the scattered light received by the light receiving element 12). A frequency analysis using FFT (Fast Fourier Transform) is performed on the signal sample value). As a result, the arithmetic circuit 146 calculates the blood flow rate Q. In particular, in the first embodiment, as will be described in detail later, the arithmetic circuit 146 includes the arithmetic circuit 143 in addition to the result of the frequency analysis of the beat signal using the FFT performed on the output of the A / D converter 145. The blood flow rate Q is calculated based on the blood flow concentration N calculated by.

  The blood flow concentration N calculated by the calculator 143 and the blood flow Q calculated by the calculator 146 are outside the blood flow calculation device 1 (or in a processing block (not shown) provided inside the blood flow calculation device 1). ) May be output at an appropriate timing.

(1-2) Operation of Blood Flow Calculation Device Next, the flow of operation of the blood flow calculation device 1 of the first embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing an operation flow of the blood flow rate calculation apparatus 1 of the first embodiment.

  As shown in FIG. 2, the laser element 11 irradiates the tube 100 with the laser beam LB (step S11). At this time, the laser element 11 preferably irradiates the flow path in the tube 100 (that is, the flow path through which blood flows) with the laser beam LB.

  Thereafter, the light receiving element 12 receives the scattered light of the laser light LB from the tube 100 (step S12). More specifically, the light receiving element 12 includes scattered light scattered by blood flowing in the tube 100 (particularly, blood cells that are moving scatterers contained in the blood) and stationary tissue ( For example, the scattered light scattered by the tube 100 itself is received. As the scattered light, forward scattered light corresponding to the transmitted light of the laser light LB irradiated to the tube 100 may be used, or back scattered light corresponding to the reflected light of the laser light LB irradiated to the tube 100. May be used.

  Thereafter, the light receiving element 12 generates a received light signal obtained by converting the received scattered light into an electrical signal (step S12). Thereafter, the light receiving element 12 outputs the generated light reception signal to the amplifier 13.

  The received light signal includes a signal component corresponding to the light intensity of the scattered light (that is, the above-described light intensity signal and a relatively low-frequency signal component). The received light signal includes a signal component corresponding to beat signal light (that is, beat signal light generated by mutual interference between scattered light scattered by blood cells, which are moving scatterers, and scattered light scattered by stationary tissue (that is, The beat signal described above includes a relatively high-frequency signal component). Here, the frequency of the scattered light scattered by the blood cell that is the moving scatterer is compared with the frequency of the scattered light scattered by the stationary tissue, and the laser Doppler action corresponding to the blood flow velocity v. Has changed. Accordingly, the signal component corresponding to the beat signal light (that is, the beat signal) includes a signal component indicating a change in frequency according to the blood flow velocity v.

  Thereafter, the amplifier 13 converts the received light signal output from the light receiving element 12 (that is, the received light signal corresponding to the scattered light received by the light receiving element 12) into a voltage signal and then amplifies it (step S13). Thereafter, the amplifier 13 outputs the amplified light reception signal to the arithmetic circuit 14. More specifically, the amplifier 13 outputs the amplified light reception signal to both the LPF 141 and the HPF 144.

  After that, the LPF 141 cuts signal components in frequency bands other than the low-frequency signal component among the signal components included in the light reception signal output from the amplifier 13. As a result, the LPF 141 acquires a light intensity signal corresponding to the low-frequency signal component among the signal components included in the output of the amplifier 13 (step S14). Thereafter, the LPF 141 outputs the acquired light intensity signal to the A / D converter 142.

  Thereafter, the A / D converter 142 performs A / D conversion processing (that is, quantization processing) on the light intensity signal output from the LPF 141 (step S15). Specifically, for example, when the sampling period of the A / D converter 142 is Ta1, the A / D converter 142 calculates a sample value of the light intensity signal (that is, a quantized light intensity signal) for each period Ta1. Output. Thereafter, the A / D converter 142 outputs a sample value (that is, a quantized light intensity signal) of the light intensity signal corresponding to the light intensity of the scattered light received by the light receiving element 12 to the calculator 143.

  Thereafter, the calculator 143 calculates the blood flow concentration N based on the output of the A / D converter 142 (that is, the sample value of the light intensity signal corresponding to the light intensity of the scattered light received by the light receiving element 12) (step S1). S16).

  Here, with reference to FIG. 3, the calculation operation of the blood flow concentration N based on the light intensity signal will be described. FIG. 3 shows the correlation between the light intensity signal and the blood flow concentration N when the light receiving element 12 receives the forward scattered light of the laser light LB, and the case where the light receiving element 12 receives the back scattered light of the laser light LB. It is a graph which shows the correlation between the light intensity signal and blood flow concentration N.

  3A shows the correlation between the light intensity signal (specifically, the signal level of the light intensity signal) and the blood flow concentration N when the light receiving element 12 receives the forward scattered light of the laser light LB. Is shown. When the light receiving element 12 receives the forward scattered light of the laser beam LB, the higher the blood flow concentration N, the smaller the signal level of the light intensity signal. In other words, when the light receiving element 12 receives the forward scattered light of the laser light LB, the signal level of the light intensity signal increases as the blood flow concentration N decreases. In other words, the more blood cells that are scatterers that hinder the transmission of the laser beam LB, the smaller the light intensity signal.

  When the light receiving element 12 receives the forward scattered light of the laser beam LB, the calculator 143 refers to the correlation information shown in FIG. 3A held in advance inside or outside the calculator 143. Thus, the blood flow concentration N corresponding to the light intensity signal output from the A / D converter 142 is calculated. For example, when the light intensity signal output from the A / D converter 142 is P1, the calculator 143 calculates a blood flow concentration N of “NH1”. On the other hand, when the light intensity signal output from the A / D converter 142 is P2 (where P1 <P2), the calculator 143 determines the blood flow concentration N as “NL1 (where NL1 <NH1)”. Is calculated.

  On the other hand, FIG. 3B shows the relationship between the light intensity signal (specifically, the signal level of the light intensity signal) and the blood flow concentration N when the light receiving element 12 receives the backscattered light of the laser light LB. The correlation is shown. When the light receiving element 12 receives the back scattered light of the laser beam LB, the signal level of the light intensity signal increases as the blood flow concentration N increases. In other words, when the light receiving element 12 receives the backscattered light of the laser light LB, the signal level of the light intensity signal becomes smaller as the blood flow concentration N is lower. That is, the more the blood cells, which are scatterers that reflect the laser beam LB, are contained in the blood, the greater the light intensity signal.

  When the light receiving element 12 receives the back scattered light of the laser beam LB, the computing unit 143 refers to the correlation information shown in FIG. 3B held in advance inside or outside the computing unit 143. Thus, the blood flow concentration N corresponding to the light intensity signal output from the A / D converter 142 is calculated. For example, when the light intensity signal output from the A / D converter 142 is P1, the calculator 143 calculates a blood flow concentration N of “NL2”. On the other hand, when the light intensity signal output from the A / D converter 142 is P2 (where P1 <P2), the calculator 143 determines the blood flow concentration N as “NH2 (where NL2 <NH2)”. Is calculated.

  FIGS. 3A and 3B show examples in which the correlation between the light intensity signal and the blood flow concentration N is shown in a graph. However, the calculator 143 is not limited to the graph indicating the correlation between the light intensity signal and the blood flow concentration N, and any information indicating the correlation between the light intensity signal and the blood flow concentration N (for example, The blood flow concentration N according to the intensity of the optical signal output from the A / D converter 142 may be calculated by referring to a mathematical formula, a table, a map, or the like.

  In the first embodiment, the computing unit 143 is configured to calculate the blood flow concentration N based on the correlation information indicating the correlation between the light intensity signal and the blood flow concentration N shown in FIGS. Is calculated. Therefore, the “blood flow concentration N” in the first embodiment is substantially synonymous with the concentration of blood cells contained in blood (that is, blood cells as scatterers). However, as the blood flow concentration N, other concentrations (for example, concentrations of substances other than blood cells contained in blood, etc.) may be used.

  Referring back to FIG. 2, the HPF 144 is the signal component included in the light reception signal output from the amplifier 13, following or in parallel with the blood flow concentration N calculation operation in steps S <b> 14 to S <b> 16. Cut signal components in frequency bands other than the high frequency signal components. As a result, the HPF 144 acquires a beat signal corresponding to a high frequency signal component among the signal components included in the output of the amplifier 13 (step S17). Thereafter, the HPF 144 outputs the acquired beat signal to the A / D converter 145.

  Thereafter, the A / D converter 145 performs A / D conversion processing (that is, quantization processing) on the beat signal output from the HPF 144 (step S18). Specifically, for example, when the sampling period of the A / D converter 145 is Ta2, the A / D converter 145 outputs a beat signal sample value (that is, a quantized beat signal) for each period Ta2. . Thereafter, the A / D converter 145 outputs the sample value of the beat signal (that is, the quantized beat signal) that is the interference component of the scattered light received by the light receiving element 12 to the calculator 146.

  Thereafter, the calculator 146 outputs the output of the A / D converter 145 (that is, the sample value of the beat signal that is an interference component of the scattered light received by the light receiving element 12) and the output of the calculator 143 (that is, the blood flow concentration N). Based on this, the blood flow rate Q is calculated (step S19).

(1-3) Blood Flow Volume Q Calculation Operation Next, the blood flow concentration N calculation operation in step S19 in FIG. 2 will be described with reference to FIGS. FIG. 4 shows a power spectrum (that is, frequency f-power P (f) characteristic) obtained by performing FFT on the sample value of the beat signal when the blood flow velocity v is relatively fast, and the blood flow velocity v. It is a graph which shows the power spectrum obtained by performing FFT with respect to the sample value of a beat signal, when is relatively late. FIG. 5 shows the power signal obtained by performing FFT on the sample value of the beat signal when the blood flow concentration N is relatively high and the sample value of the beat signal when the blood flow concentration N is relatively low. It is a graph which shows both each ideal value and the actual value of the power spectrum obtained by performing FFT with respect to it. FIG. 6 is a graph showing the correlation between the blood flow velocity v and the average frequency Fm of the power spectrum for each blood flow concentration N. FIG. 7 is a graph showing the relationship between the blood flow concentration N and each of the inclination correction value A and the intercept correction value B applied when calculating the blood flow velocity v from the average frequency Fm of the power spectrum.

  When calculating the blood flow rate Q, the calculator 146 first performs FFT on the output of the A / D converter 145 (that is, the sample value of the beat signal that is the interference component of the scattered light received by the light receiving element 12). (Fast Fourier Transform) is performed. As a result, the calculator 146 acquires the power spectrum shown in FIG. 4 (that is, the power spectrum indicating the power P (f) of the beat signal for each frequency f).

  As shown in FIG. 4, when the blood flow velocity v is relatively fast (that is, the blood flow rate Q is relatively large), the blood flow velocity v is relatively slow (that is, the blood flow rate Q is relatively high). The power P (f) of the beat signal in a relatively low frequency region is smaller than in the case of (smaller). In addition, when the blood flow velocity v is relatively fast (that is, the blood flow rate Q is relatively large), the blood flow velocity v is relatively slow (that is, the blood flow rate Q is relatively small). Compared with the above, the power P (f) of the beat signal in a relatively high frequency region is increased.

  Considering the power spectrum shown in FIG. 4, the blood flow velocity v depends on the average frequency Fm on the power spectrum. That is, the higher the average frequency Fm, the faster the blood flow velocity v. In other words, the lower the average frequency Fm, the slower the blood flow velocity v. Further, under the condition that the tubes 100 are the same, the blood flow velocity v and the blood flow rate Q have a positive correlation. That is, the blood flow rate Q increases as the blood flow velocity v increases. In other words, the blood flow rate Q becomes smaller as the blood flow velocity v becomes slower.

  The computing unit 146 calculates the blood flow rate Q in consideration of the relationship among the average frequency Fm, the blood flow velocity v, and the blood flow rate Q. Specifically, the calculator 146 calculates the average frequency Fm using Equation 1. Here, f is the frequency of the beat signal, and P (f) is the power of the beat signal having the frequency f. Thereafter, the computing unit 146 calculates the blood flow velocity v using Equation 2. However, K is a flow velocity conversion coefficient. Thereafter, the computing unit 146 calculates the blood flow rate Q using Equation 3. However, L is a flow rate conversion coefficient.

  If it is assumed that the blood flow concentration N is not considered at all, the computing unit 146 can calculate the blood flow rate Q using the above-described Equations 1 to 3. However, in the first embodiment, the computing unit 146 calculates the blood flow rate Q in consideration of the blood flow concentration N. This is because the power spectrum of the beat signal varies according to the blood flow concentration N as shown in FIGS.

  Specifically, FIG. 5A shows that when the blood flow concentration N is relatively high, the power spectrum (see solid line) obtained by performing FFT on the sample value of the beat signal and the blood flow concentration N are as follows. Each ideal value (that is, theoretical value) of the power spectrum (see the dotted line) obtained by performing FFT on the sample value of the beat signal when it is relatively low is shown. Ideally (in other words, theoretically), as the blood flow concentration N decreases, the power spectrum moves in parallel along the vertical axis (that is, the power axis). That is, ideally, when the blood flow concentration N changes, the power spectrum does not move along the horizontal axis (that is, the frequency axis), but is parallel only along the vertical axis (that is, the power axis). Move to. As a result, ideally, the average frequency Fm calculated from the power spectrum does not change depending on the blood flow concentration N. Therefore, ideally, the calculator 146 should be able to calculate the blood flow rate Q using the above-described Equations 1 to 3 regardless of the value of the blood flow concentration N.

  However, in reality, as shown in FIG. 5B, the power spectrum changes in a manner different from that in FIG. 5B shows that when the blood flow concentration N is relatively high, the power spectrum (see the solid line) obtained by performing FFT on the sample value of the beat signal and the blood flow concentration N are relatively high. The actual values (that is, actually measured values) of the power spectrum (see the dotted line) obtained by performing FFT on the sample value of the beat signal when it is low are shown.

  Actually, as shown in FIG. 5, when the blood flow concentration N is relatively high, the blood cell unit which is a scatterer in the blood is compared with the case where the blood flow concentration N is relatively low. The number per volume is relatively large. Therefore, when the blood flow concentration N is relatively high, the power P (f) of the beat signal increases uniformly over the entire frequency region as compared with the case where the blood flow concentration N is relatively low. . On the other hand, when the blood flow concentration N is relatively low, the number of blood cells, which are scatterers in the blood, per unit volume is relatively small compared to the case where the blood flow concentration N is relatively high. Become. Therefore, when the blood flow concentration N is relatively low, the power P (f) of the beat signal is uniformly reduced over the entire frequency region as compared with the case where the blood flow concentration N is relatively high. .

  However, since the power P (f) of the beat signal relatively decreases when the blood flow concentration N is relatively low, the power P (f) when the blood flow concentration N is relatively low is shown in FIG. (B) is more strongly affected by the amplifier noise (specifically, amplifier noise caused by the parasitic capacitance of the input terminal of the amplifier 13) indicated by the alternate long and short dash line in FIG. As shown in FIG. 5B, the amplifier noise has a characteristic that it increases as the frequency f increases. For this reason, when the blood flow concentration N is relatively low, the power P (f) particularly in a relatively high frequency region is likely to be dominated by the amplifier noise. Therefore, when the blood flow concentration N is relatively low, the power P (f) particularly in a relatively high frequency region does not decrease as much as the ideal value (theoretical value).

  As a result, in reality, the average frequency Fm calculated from the power spectrum changes depending on the blood flow concentration N. More specifically, even when the blood flow velocity v or the blood flow rate Q is the same, the average frequency Fm when the blood flow concentration N is relatively low is when the blood flow concentration N is relatively high. Higher than the average frequency Fm. Therefore, from the viewpoint of calculating the blood flow rate Q with high accuracy, the computing unit 146 preferably calculates the blood flow rate Q while taking the blood flow concentration N into consideration. For this reason, in the first embodiment, the calculator 146 calculates the blood flow rate Q while taking the blood flow concentration N into consideration.

  A measure to reduce the influence of the amplifier noise by increasing the power of the laser beam LB irradiated from the laser element 11 (as a result, increasing the power on the power spectrum) can be considered. However, when the power of the laser beam LB is increased, there is a demerit that the power consumption of the blood flow rate calculation device 1 is increased. Therefore, in the first embodiment, the increase in power consumption of the blood flow rate calculation device 1 is suppressed by calculating the blood flow rate Q in consideration of the blood flow concentration N.

  Specifically, as shown in FIG. 6, the computing unit 146 uses the correlation information indicating the correlation between the average frequency Fm and the blood flow velocity v for each blood flow concentration N to calculate the blood flow concentration N. The considered blood flow rate Q is calculated. FIG. 6 shows the correlation between the average frequency Fm when the blood flow concentration N is NL and the blood flow velocity v, and the average frequency when the blood flow concentration N is NM (where NM> NL). Correlation between Fm and blood flow velocity v and correlation between average frequency Fm and blood flow velocity v when blood flow concentration N is NH (where NH> NM> NL) ing.

  For example, when the blood flow concentration N output from the calculator 143 is NL, and the average frequency Fm calculated from the above equation 1 is f1, the calculator 146 is based on the correlation information shown in FIG. Then, VL is calculated as the blood flow velocity v. Thereafter, the computing unit 146 calculates the blood flow rate Q by applying the blood flow velocity v = VL calculated with respect to Equation 3 described above.

  Similarly, when the blood flow concentration N output from the calculator 143 is NM and the average frequency Fm calculated from the above Equation 1 is f1, the calculator 146 displays the correlation information shown in FIG. Based on this, VM (however, VM> VL) is calculated as the blood flow velocity v. Thereafter, the computing unit 146 calculates the blood flow rate Q by applying the blood flow velocity v = VM calculated with respect to Equation 3 described above.

  Similarly, when the blood flow concentration N output from the calculator 143 is NH and the average frequency Fm calculated from the above equation 1 is f1, the calculator 146 displays the correlation information shown in FIG. Based on this, VH (where VH> VM) is calculated as the blood flow velocity v. Thereafter, the computing unit 146 calculates the blood flow rate Q by applying the blood flow velocity v = VH calculated with respect to Equation 3 described above.

  As can be seen from the correlation information shown in FIG. 6, the correlation information focuses on the same average frequency Fm so that the blood flow velocity v increases as the blood flow concentration N increases. A correlation between the flow velocity v and the blood flow concentration N is shown. Since the correlation information defines a correlation having such characteristics, the influence of amplifier noise when calculating the blood flow rate Q is eliminated.

  Here, the correlation between the average frequency Fm shown in FIG. 6 and the blood flow velocity v is substantially approximated by a linear expression (however, when viewed in more detail, the average frequency Fm shown in FIG. The correlation between the blood flow velocity v is expressed by a mathematical expression other than the linear expression). Specifically, the correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NL is flow velocity v = (1 / slope KL) × (average frequency Fm−intercept CL). Approximated by mathematical formula. In other words, the correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NL is approximated by the following equation: average frequency Fm = slope KL × flow velocity v + intercept CL. The correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NM is: flow velocity v = (1 / slope KM (where KM <KL)) × (average frequency Fm− It is approximated by a mathematical formula called intercept CM (where CM <CL). In other words, the correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NM is approximated by the equation: average frequency Fm = slope KM × flow velocity v + intercept CM. The correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NH is: flow velocity v = (1 / slope KH (where KH <KM)) × (average frequency Fm− It is approximated by a mathematical formula of intercept CH (where CH <CM). In other words, the correlation between the average frequency Fm and the blood flow velocity v when the blood flow concentration N is NH is approximated by the equation: average frequency Fm = slope KH × flow velocity v + intercept CH.

  Therefore, in the first embodiment, the arithmetic unit 146, in addition to or instead of directly using the correlation information shown in FIG. 6, has an inclination correction value A (inclination shown in FIG. , Slope KL, slope KM, and slope KH) (refer to FIG. 7A) and intercept correction value B (intercept shown in FIG. 6, refer to FIG. 7B) and blood flow. You may use the correlation information which shows the correlation between N by density | concentration.

  Specifically, the correlation information illustrated in FIG. 7A indicates a correlation between the inclination correction value A and the blood flow concentration N. Therefore, when the blood flow concentration N output from the calculator 143 is NL, the calculator 146 refers to the correlation information shown in FIG. calculate. Similarly, when the blood flow concentration N output from the calculator 143 is NM, the calculator 146 refers to the correlation information shown in FIG. Is calculated. Similarly, when the blood flow concentration N output from the calculator 143 is NH, the calculator 146 refers to the correlation information shown in FIG. Is calculated.

  Further, the correlation information shown in FIG. 7B shows the correlation between the intercept correction value B and the blood flow concentration N. Therefore, when the blood flow concentration N output from the calculator 143 is NL, the calculator 146 calculates CL as the intercept correction value B by referring to the correlation information shown in FIG. . Similarly, when the blood flow concentration N output from the calculator 143 is NM, the calculator 146 calculates CM as the intercept correction value B by referring to the correlation information shown in FIG. To do. Similarly, when the blood flow concentration N output from the calculator 143 is NH, the calculator 146 calculates CH as the intercept correction value B by referring to the correlation information shown in FIG. To do.

  When the correlation information shown in FIGS. 7A and 7B is used, the computing unit 146 calculates the average frequency Fm using Equation 1 described above. Thereafter, the arithmetic unit 146 calculates the intercept calculated from the average frequency Fm calculated for Equation 4 and the slope correction value A calculated from the correlation information shown in FIG. 7A and the correlation information shown in FIG. By applying the correction value B, the blood flow velocity v is calculated. Thereafter, the computing unit 146 calculates the blood flow rate Q by applying the blood flow velocity v calculated with respect to Equation 3 described above.

  In addition, it is preferable that the blood flow rate calculation apparatus 1 holds the correlation information shown in FIG. 6 and the correlation information shown in FIGS. 7A and 7B in advance. For example, the blood flow rate calculation device 1 may create the correlation information described above in advance by calculating the blood flow rate Q and the like for a plurality of types of blood having different blood flow concentrations.

  Moreover, FIG.6 and FIG.7 (a) and FIG.7 (b) have shown the example which shows a correlation with a graph. However, the computing unit 146 may calculate the blood flow rate Q by referring to arbitrary information (for example, a mathematical formula, a table, or a map) indicating the correlation, not limited to the graph indicating the correlation.

  As described above, according to the blood flow rate calculation device 1 of the first embodiment, the blood flow rate Q can be calculated suitably (in other words, with high accuracy) while taking the blood flow concentration N into consideration.

  Note that the above-described calculation operation of the blood flow Q in consideration of the blood flow concentration N (that is, the calculation operation using Formula 1, Formula 3 and Formula 4, and FIGS. 6 and 7) is merely an example. Therefore, the blood flow rate calculation device 1 may calculate the blood flow rate Q in consideration of the blood flow concentration N in other modes. In short, as long as the blood flow rate calculation device 1 can calculate the blood flow rate Q so that the influence of the amplifier noise corresponding to the difference in the blood flow concentration N can be eliminated, the blood flow rate Q can be calculated in any manner. It may be calculated.

  Further, as described above, the frequency of the light intensity signal used for calculating the blood flow concentration N is typically 1 kHz or less, and the frequency of the beat signal used for calculating the blood flow Q is typical. Is 1 kHz or more. Therefore, the sampling period of the A / D converter 142 for calculating the blood flow concentration N (that is, the period for performing quantization) is longer than the sampling period of the A / D converter 145 for calculating the blood flow rate Q. Also good. Similarly, the calculation cycle of the calculator 143 for calculating the blood flow concentration N (that is, the cycle for calculating the blood flow concentration N) is the calculation cycle of the calculator 146 for calculating the blood flow Q (that is, It may be longer than the period in which the blood flow rate Q is calculated.

  In the above description, the blood flow rate calculation device 1 calculates both the blood flow rate Q and the flow velocity v. However, under the condition that the tubes 100 are the same, the blood flow rate Q and the flow velocity v have a positive correlation. That is, as the blood flow rate Q of blood flowing through a certain tube 100 increases, the flow velocity v of blood flowing through the tube 100 increases. On the other hand, there is a correlation that if the blood flow rate Q of blood flowing through a certain tube 100 decreases, the flow velocity v of blood flowing through the tube 100 decreases. Therefore, it can be said that the calculation of the blood flow rate Q and the calculation of the flow velocity v are substantially the same. That is, the calculation of the flow velocity v substantially corresponds to the indirect calculation of the blood flow rate Q, and the calculation of the blood flow rate Q substantially corresponds to the indirect calculation of the flow velocity v. Therefore, the blood flow rate calculation device 1 does not have to calculate either the blood flow rate Q or the flow velocity v while calculating either the blood flow rate Q or the flow velocity v.

(2) Second Example Next, the blood flow rate calculation device 2 of the second example will be described with reference to FIG. FIG. 8 is a block diagram showing the configuration of the blood flow rate calculation device 2 of the second embodiment. In the following description, the same reference numerals and step numbers are assigned to the same configurations and operations as those of the blood flow rate calculation device 1 of the first embodiment, and detailed description thereof is omitted.

  As shown in FIG. 8, the blood flow rate calculation device 2 of the second embodiment differs from the blood flow rate calculation device 1 of the first embodiment in that it further includes a light receiving element 22 and an amplifier 23. Yes. Furthermore, in the blood flow rate calculation device 2 of the second embodiment, the LPF 141 receives light according to the output of the amplifier 23 (that is, the scattered light received by the light receiving element 22), compared to the blood flow rate calculation device 1 of the first embodiment. Signal component in the frequency band other than the low-frequency signal component among the signal components included in the signal) and the HPF 144 outputs the output of the amplifier 13 (that is, the received light signal corresponding to the scattered light received by the light receiving element 12). The difference is that the signal components in the frequency band other than the high-frequency signal component are cut out of the included signal components. Other components included in the blood flow rate calculation device 2 of the second embodiment may be the same as other components included in the blood flow rate calculation device 1 of the first embodiment.

  The light receiving element 22 receives the scattered light of the laser light LB irradiated on the tube 100. The light receiving element 22 generates a received light signal obtained by converting the received scattered light into an electrical signal.

  The light receiving element 22 receives the forward scattered light corresponding to the transmitted light of the laser light LB irradiated to the tube 100, and receives the back scattered light corresponding to the reflected light of the laser light LB irradiated to the tube 100. 12 may receive light. Alternatively, the light receiving element 22 receives the backscattered light corresponding to the reflected light of the laser light LB irradiated on the tube 100, and receives the forward scattered light corresponding to the transmitted light of the laser light LB irradiated on the tube 100. 12 may receive light. Both the light receiving element 12 and the light receiving element 22 may receive forward scattered light corresponding to the transmitted light of the laser light LB irradiated to the tube 100. Alternatively, both the light receiving element 12 and the light receiving element 22 may receive backscattered light corresponding to the reflected light of the laser beam LB irradiated on the tube 100.

  The amplifier 23 amplifies the light receiving signal, which is a current signal output from the light receiving element 22, after converting it into a voltage signal.

  Such a blood flow rate calculation device 2 of the second embodiment can preferably enjoy the same effects as the various effects that the blood flow rate calculation device 1 of the first embodiment can enjoy.

  In addition, according to the blood flow rate calculation device 2 of the second embodiment, the light receiving element 12 mainly used for calculating the blood flow rate Q and the light receiving element 22 mainly used for calculating the blood flow concentration N are provided. Prepared separately.

  For this reason, the light receiving area of the light receiving element 12 used mainly for calculating the blood flow rate Q can be relatively reduced. For example, the light receiving area of the light receiving element 12 mainly used for calculating the blood flow rate Q can be made smaller than the light receiving area of the light receiving element 22 mainly used for calculating the blood flow concentration N. As a result, the influence of the noise of the amplifier 13 that causes a decrease in the calculation accuracy of the blood flow rate Q is relatively reduced (for example, the parasitic capacitance of the input terminal of the amplifier 13 that causes the noise is relatively reduced). Can be reduced).

  On the other hand, the light receiving area of the light receiving element 22 used mainly for calculating the blood flow concentration N can be relatively increased. For example, the light receiving area of the light receiving element 22 mainly used for calculating the blood flow concentration N can be made larger than the light receiving area of the light receiving element 12 mainly used for calculating the blood flow rate Q. As a result, the S / N ratio of the light intensity signal used for calculating the blood flow concentration N can be relatively improved.

  The light receiving area between the light receiving element 12 and the laser element 11 can be relatively reduced so that both the light receiving element 12 and the light receiving element 22 can receive the scattered light of the laser light LB. This distance may be shorter than the distance between the light receiving element 22 and the laser element 11 that can relatively increase the light receiving area. In other words, the light receiving element 12 capable of relatively reducing the light receiving area is preferably as close to the laser element 11 as possible.

(3) Third Example Next, the blood flow rate calculation device 3 of the third example will be described with reference to FIG. FIG. 9 is a block diagram showing the configuration of the blood flow rate calculation device 3 of the third embodiment. In the following description, the same reference numerals and step numbers are assigned to the same configurations and operations as those of the blood flow rate calculation device 1 of the first embodiment, and detailed description thereof is omitted.

  As shown in FIG. 9, the blood flow rate calculation device 3 of the third embodiment is further provided with an APC (Automatic Power Control) circuit 31 as compared with the blood flow rate calculation device 1 of the first embodiment. Is different. Other components included in the blood flow rate calculation device 3 of the third embodiment may be the same as other components included in the blood flow rate calculation device 1 of the first embodiment.

The APC circuit 31 includes a back monitor 311, an amplifier 312, a subtractor 313, and a controller 314. The back monitor 311 is a laser beam LB emitted from the laser element 11 (particularly, the emission end face of the laser element 11). The laser beam LB) leaking from the end surface on the opposite side of the laser beam is received. The back monitor 311 generates a light reception signal obtained by converting the received laser light LB into an electrical signal.

  The amplifier 312 amplifies the light reception signal, which is a current signal output from the back monitor 311, after converting it into a voltage signal.

  The subtractor 313 subtracts the voltage signal output from the amplifier 312 from a predetermined target signal (specifically, a signal corresponding to the target power of the laser beam LB emitted from the laser element 11). That is, the subtracter 313 calculates an error from the target power of the power of the laser beam LB currently emitted from the laser element 11. The subtractor 313 outputs an error signal indicating the error to the controller 314.

  The controller 314 performs phase compensation for executing stable negative feedback on the error signal output from the subtractor 313. Thereafter, the controller 314 controls the laser element 11 based on the error signal subjected to phase compensation. As a result, the laser element 11 emits the laser beam LB whose power is changed by an amount corresponding to the error signal subjected to phase compensation.

  Such a blood flow rate calculation device 3 of the third embodiment can preferably enjoy the same effects as the various effects that the blood flow rate calculation device 1 of the first embodiment can enjoy.

  In addition, according to the blood flow rate calculation device 3 of the third embodiment, the APC circuit 31 can cause the power of the laser beam LB emitted from the laser element 11 to follow the target power. Therefore, the laser element 11 can irradiate the laser beam LB stably. As a result, the blood flow rate calculation device 3 can calculate the blood flow rate Q and the blood flow concentration N more suitably (in other words, with higher accuracy) by using the stable laser beam LB.

  The blood flow rate calculation device 3 may include a front monitor that receives the laser light LB emitted from the laser element 11 via a beam splitter in addition to or instead of the back monitor 311.

(4) Fourth Example Next, with reference to FIG. 10, the blood flow rate calculation device 4 of the fourth example will be described. FIG. 10 is a block diagram showing the configuration of the blood flow rate calculation device 4 of the fourth embodiment. In the following description, the same reference numerals and step numbers are assigned to the same configurations and operations as those of the blood flow rate calculation device 2 of the second embodiment, and detailed description thereof is omitted.

  As shown in FIG. 10, the blood flow rate calculation device 4 of the fourth embodiment is different from the blood flow rate calculation device 2 of the second embodiment in that it further includes an LED element 41. Other components included in the blood flow rate calculation device 4 of the fourth embodiment may be the same as other components included in the blood flow rate calculation device 2 of the second embodiment.

  The LED element 41 irradiates the tube 100 with measurement light for mainly calculating the blood flow concentration N. At this time, it is preferable that the LED element 41 irradiates the measurement light to the flow path in the tube 100 (that is, the flow path through which blood flows). In addition, in order to reduce the possibility that blood oxygen saturation affects the blood flow concentration N, the wavelength of the measurement light may be 805 nm, which is a wavelength that does not depend on the blood oxygen saturation. preferable.

  On the other hand, the laser element 11 irradiates the tube 100 with laser light LB mainly for calculating the blood flow rate Q. Here, when the blood flow rate Q is calculated, a beat signal resulting from the mutual interference of scattered light is detected. Therefore, it is preferable that the light irradiated to the tube 100 to calculate the blood flow Q has a relatively high coherence and a relatively high monochromaticity in order to make it easier to detect a beat signal. Therefore, the laser element 11 irradiates the laser beam LB having such characteristics in order to calculate the blood flow rate Q. The wavelength of the laser beam LB may be 780 nm from the viewpoint of easy availability of the laser element 11.

  In order to prevent interference between the laser beam LB and the measurement beam, the region on the tube 100 irradiated with the laser beam LB from the laser element 11 is the region on the tube 100 irradiated with the measurement beam from the LED element 41. Preferably they are different. In other words, in order to prevent interference between the laser light LB and the measurement light, the region on the tube 100 irradiated with the laser light LB from the laser element 11 is the region on the tube 100 irradiated with the measurement light from the LED element 41. It is preferable that the predetermined distance is more than a predetermined distance. Alternatively, the irradiation timing of the measurement light and the laser light LB may be adjusted to prevent mutual interference.

  In the fourth embodiment, the light receiving element 12 receives the scattered light of the laser light LB irradiated from the laser element 11 to the tube 100. On the other hand, the light receiving element 22 receives the scattered light of the measurement light emitted from the LED element 41 to the tube 100.

  Such a blood flow rate calculation device 4 of the fourth embodiment can preferably enjoy the same effects as the various effects that the blood flow rate calculation device 2 of the second embodiment can enjoy.

  In addition, according to the blood flow rate calculation device 4 of the fourth embodiment, the laser element 11 mainly used for calculating the blood flow rate Q and the LED element 41 mainly used for calculating the blood flow concentration N are provided. Prepared separately. Therefore, the blood flow rate Q is calculated using the laser beam LB suitable for calculating the blood flow rate Q, and the blood flow concentration N is calculated using the measurement light suitable for calculating the blood flow concentration. The Therefore, the blood flow rate calculation device 4 can more preferably calculate the blood flow rate Q and the blood flow concentration N.

(5) Specific Examples of Light Receiving Element 12 and Amplifier 13 Subsequently, with reference to FIG. 11, the light receiving element 12 provided in the blood flow rate calculating device 1 of the first embodiment to the blood flow rate calculating device 4 of the fourth embodiment. A specific example of the amplifier 13 will be described. FIG. 11 is a block diagram showing the configuration of a specific example of the light receiving element 12 and the amplifier 13 provided in the blood flow rate calculation device 1 of the first example to the blood flow rate calculation device 4 of the fourth example.

  As shown in FIG. 11, the light receiving element 12 includes a PIN photodiode 121 and a PIN photodiode 122. The PIN photodiode 121 and the PIN photodiode 122 are connected in series so that the anodes are connected to each other. The cathode of the PIN diode 121 is connected to the amplifier 13 (in particular, the positive phase input terminal of the fully-differential amplifier 131 provided in the amplifier 13). The cathode of the PIN diode 122 is connected to the amplifier 13 (particularly, the reverse phase input terminal of the fully-differential amplifier 131 provided in the amplifier 13).

  The light receiving element 12 uses the differential current IdtC (= IdtB−IdtA) between the current IdtA output from the PIN photodiode 121 and the current IdtB output from the PIN photodiode 122 as a received light signal as an amplifier 13 (in particular, the amplifier 13). Output to the positive-phase input terminal of the fully-differential amplifier 131 included in. In addition, the light receiving element 12 outputs the differential current −IdtC in which the polarity of the differential current IdtC is inverted to the amplifier 13 (particularly, the reverse phase input terminal of the fully differential amplifier 131 included in the amplifier 13) as a light receiving signal. .

  According to the light receiving element 12 having such a configuration, the DC component of the current IdtA output from the PIN photodiode 121 and the DC component of the current IdtB output from the PIN photodiode 122 are offset. Therefore, the light receiving element 12 can output a differential current IdtC mainly including an AC component corresponding to a signal component (that is, a beat signal) included in the scattered light as a light receiving signal. For this reason, the S / N ratio in the amplifier 13 can be relatively improved.

  The amplifier 13 includes a fully differential amplifier 131, a feedback resistor 132, a feedback resistor 133, and a next-stage amplifier 134.

  The fully differential amplifier 131 converts the differential current IdtC input to the positive phase input terminal In + into a voltage signal, and then outputs the voltage signal from the negative phase output terminal Out−. Similarly, the fully differential amplifier 131 converts the differential current −IdtC input to the negative phase input terminal In− into a voltage signal, and then outputs the voltage signal from the positive phase output terminal Out +. That is, the fully-differential amplifier 131 operates as a transimpedance amplifier that converts the currents input to the positive phase input terminal In + and the negative phase input terminal In− into voltages independently, and outputs them differentially. The reference potential of the fully differential amplifier 131 is input to the fully differential amplifier 131 via the reference potential terminal Vref.

  Here, the feedback resistor 132 connected between the positive phase input terminal In + and the negative phase output terminal Out− performs negative feedback. A feedback resistor 133 connected between the negative phase input terminal In− and the positive phase output terminal Out + performs negative feedback. Therefore, the potential difference between the positive phase input terminal In + and the reference potential terminal Vref is zero (or a value that can be regarded as zero). Similarly, the potential difference between the negative phase input terminal In− and the reference potential terminal Vref is zero (or a value that can be regarded as zero). Accordingly, the potential of the positive phase input terminal In + is the same as (or can be regarded as the same as) the potential of the negative phase input unit In−. Accordingly, the cathode potential of the PIN photodiode 121 connected to the positive phase input terminal In + is the same as (or the same as) the cathode potential of the PIN photodiode 122 connected to the negative phase input terminal In−. It is in a state where it can be seen. For this reason, each of the PIN photodiode 121 and the PIN photodiode 122 operates in a zero bias state. Therefore, the dark current generated in the laser element 11 can be reduced or eliminated. For this reason, since noise due to fluctuations in dark current is reduced, the S / N ratio in the amplifier 13 is relatively improved.

  The next-stage amplifier 134 functions as a so-called instrumentation amplifier, and amplifies and outputs the differential signal output from the fully differential amplifier 131.

  In addition, you may combine suitably a part of each structure demonstrated in 1st Example-4th Example. Even in this case, the blood flow rate calculation device obtained by appropriately combining a part of the configurations described in the first to fourth embodiments can suitably enjoy the various effects described above.

  In addition, the present invention can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and a blood flow rate calculation device and method involving such changes are also included in the present invention. Included in technical thought.

1, 2, 3, 4 Blood flow rate calculation device 11 Laser element 12, 22 Light receiving element 13, 23 Amplifier 141 LPF
144 HPF
142, 145 A / D converter 143, 146 arithmetic unit 311 back monitor 312 amplifier 313 subtractor 314 controller 41 LED element

Claims (1)

An irradiating means capable of irradiating at least a laser beam to an object to be measured in which a fluid flows;
A light receiving means for receiving the laser light irradiated to the object to be measured and generating a light reception signal by converting the received laser light into an electrical signal;
Calculating means for calculating the flow rate of the fluid,
The calculation means calculates the flow rate calculated when the fluid concentration is low under the same frequency change of the light reception signal caused by the Doppler shift of the laser light irradiated to the measurement target. The flow rate is calculated so as to be smaller than the flow rate calculated when the concentration is high.

Images