JPS60152916A - Apparatus for measuring amount of ultrafiltration - Google Patents

Abstract

PURPOSE:To perform accurate measurement without using highly accurate flowmeter, by flowing liquid having the same flow rate to the first flowmeter for receiving dialysis liquid and the second flowmeter for draining liquid, and calibrating the second flowmeter based on the respective outputs, with the characteristic of the first flowmeter as a reference. CONSTITUTION:By the control of a control part 21, modes can be switched to a measuring mode, by which the amount of ultrafiltration is measured and to a calibrating mode, by which a flowmeter 17 is calibrated. In the measuring mode, dialysis liquid in a liquid supply line 11 flows through a flow rate sensor 16a of a flowmeter 16, which has been calibrated or whose coefficient indicating the characteristic is known, ports (a)-(b) of a directional control valve 22, a dialyzer 12, ports (b)-(a) of a directional control valve 23 and a flow rate sensor 17a of the flowmeter 17. In the calibration mode, the liquid flows through the flow rate sensor 16a, the ports (a)-(c) of the directional control valve 22, a bypass 24, the ports (c)-(a) of the directional control valve 23 and the flow rate sensor 17a. An operating part 25 computes the characteristic coefficient of the flowmeter 17 based on the flow rate signal, and the result is displayed on a display part 26.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrafiltration rate measuring device that measures the difference between the flow rate of dialysis fluid flowing out from a dialyzer and the flow rate of dialysate flowing into the dialyzer as an ultrafiltration rate.

<Prior Art> As shown in FIG. 1, in a dialysis apparatus, dialysate is supplied to a dialyzer 12 through a fluid supply line 11, and dialysis fluid from the dialyzer 12 is discharged through a drainage line 13. Dialyzer 1
2 is supplied with the patient's blood through a blood line 14,
Blood from which waste products have been removed by dialysis in the dialyzer 12 is returned to the patient through a blood line 15.

In the conventional ultraflow measuring device, the liquid supply line 11
Flowmeters 16 and 17 are provided in the and drainage line 13, respectively, and the flowmeter 16 measures the flow rate Fi of the dialysate flowing into the dialyzer 12 to obtain a measured value Vl, and the dialysis fluid discharged from the dialyzer 12 is measured by the flowmeter 16. The flow rate F0 of is measured by the flowmeter 17 and the measured value v
0 and V as the ultrate excess. -I was wearing Vi.

However, this conventional ultrafiltration rate measuring device has the following problems. That is, flowmeters generally have measurement errors, and if the flow rate and the flow rate sensor output signal of the F1 flow meter are E, then the following equation holds true: p=kF+E. Here, k is the flow rate-sensor output signal conversion coefficient, and Eo is the zero error, that is, the sensor output signal when the flow rate F is zero. Also, if the flowmeter output value is V, then between V and E, ■=μE
+ε holds true. Here, μ is the sensor output signal-flowmeter output value conversion coefficient, and ε is the zero error, that is, the flowmeter output value output when the sensor output signal is zero.

Normally, this flowmeter output value ■ is used as the final output in most cases, and in the conventional ultrafiltration rate measuring device shown in FIG. 1, the output value v1 of the flowmeter 16 is V, =μIEI+ε
l=μs (ktF1+Eot)lε1 Also, the output value v2 of the flowmeter 17 is: ■2=μ2E2+ε2=μz (kzFO+Eo2)+
Each can be expressed as g2. Therefore, the ultrafiltration rate is Vt”
b=μzEz+t2(μ+Et+'t)=μz (kg
FO+EO2)+ε2−μs (kt Ft+Eo+
) − ε1 = (μ2 to 2F0 − μ+ to +F+) + (μ2
Eo2-μIEot)+(ε2-ε1)...(1
) becomes. If both flowmeters 16 and 17 have no errors, μ2 = 2 = μ + kt = 1 * EO1 =
EO2=ε2=εl=Q. However, since errors are always included in reality, accurate measurements cannot be made when considering equation (1). When the error is zero, the sensor output signal-flow meter output value conversion coefficient and the flow rate-sensor output signal conversion coefficient are μ, respectively. If +kO, μm; μ0+Δμ! .

μ2=μ0+Δμzlct=ko+Δkl, 2=to,
+Δ can be written as 2. Using this, equation (1) becomes equation (2).

V2 Vt=(μ.+Δμ2)(ko+Δkg)Fo
(μθ+Δμm) (+ to ko+Δ)FttenC.

2 μoko(Fo F+) 10 μ0(Δ to 2Fo−Δ,
pl) 10k. (Δμ2Fo−Δμ+Ft)+(Δμ2Δ
In, F.

−Δμ, Δ + Fl ) + Co −(2) where co
-μ2 F, (1!-μ1 Eol + t2-ε1 where,
If μo-ko=1, the true value of the ultrafiltration amount is only the first term, and the other terms are errors. This error is 1. Δ
kg + Δμm, Δμ2 r EOI * Eos lε
1. It depends on the value of ε2, which varies depending on the flowmeter. For example, the flow rate flowing into the dialyzer 12 (hereinafter referred to as the inlet side flow rate) is 500 m4'min, the error of the flow meter 16 is +1 inch, and the flow rate flowing out from the dialyzer 12 (hereinafter referred to as the outlet side flow rate) is 505 m4/min. n1in, assuming that the error of the flowmeter 17 is 11% (the error of a normal flowmeter is ±1%)
% or more), the output value of the flow meter 16 is 50
51min, and the output value of flowmeter 17 is 449.9
5 wheels in. Therefore, the actual ultrafiltration amount is 5Tn4
/min, whereas the measured value is -5,051+4/min.
n11 n, the value is completely unbelievable. usually,
There is a practical problem in measuring the ultrafiltration rate if the error range is ±10 inches from the true value, but the inlet flow rate is 500 mm.
, in the case of the outlet side flow rate of 505WLVm1n, in order for the measurement error of the ultrafiltration amount to be within ±10%, (505-
500) X-fo, 1/2. =±0.25 m4/mi
A flowmeter with a resolution of n or higher is required. This is 5
The error is ±0.00m4/mln for flow rate measurement.
The accuracy is as high as 251,500 or less, that is, less than ±0.05%, and such a high-precision flowmeter is unrealistic.

In the conventional technique in which two flowmeters 16 and 17 are used and the difference in their output values is measured as the ultrafiltration amount, 2. Δμ! ,Δμ鵞+Eot+E
112 +εhε3 always occurs, making it impossible to accurately measure the amount of ultrafiltration.

<Summary of the Invention> The purpose of the present invention is to provide an apparatus for measuring the amount of ultrafiltration from the difference between the flow rate of outflow dialysis fluid and the flow rate of inflow dialysate, by using a particularly high-precision flowmeter. The purpose is to make it possible to measure the amount of ultrafiltration.

According to this invention, the mode switching means switches between a measurement mode in which dialysis is performed using a dialyzer and the amount of ultrafiltration is measured, and a calibration mode in which the characteristics of a flowmeter are calibrated to measure outflow dialysis effluent. configured so that a flow meter that measures inflow dialysate when switched to its calibration mode;
The same flow rate of liquid is allowed to flow through the flowmeter that measures the outflow dialysis fluid, and the output signal of each flowmeter at that time and the characteristics of the flowmeter that measures the inflow dialysate are determined. The values are used to calibrate the characteristics of a flow meter that measures outflow dialysis fluid relative to the characteristics of a flowmeter that measures inflow dialysate.

<Embodiment> FIG. 2 shows an embodiment of the ultrafiltration rate measuring device according to the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals. In the present invention, the control section 21 can switch between a measurement mode in which the limit offshore excess is measured and a calibration mode in which the flowmeter 17 is calibrated. In its calibration mode, flow meters 16 and 17 are allowed to flow the same flow rate of liquid simultaneously. Therefore, in this embodiment, a switching valve 22 is inserted in the liquid supply line 11 between the flow meter 16 and the dialyzer 12, and a switching valve 23 is inserted in the drain line 13 between the dialyzer 12 and the flow meter 17. is,
A side passage 24 is connected between the switching valves 22 and 23.

In the measurement mode, the dialysate in the fluid supply line 1-1 is
Flow rate sensor 16m of flow meter 16 = data of switching valve 22)a
- b - dialyzer 12 - port ba of switching valve 23 - flows through flow rate sensor 17 m of flow meter 17 and is discharged through drain line 13 . On the other hand, in the calibration mode, the dialysate is caused to flow through the flow rate sensor 16a, the port (ac) of the switching valve 22, the bypass 24, the port ea of the switching valve 23, and the flow rate section 17m.

The flow rate sensor 16a has already been calibrated, and the coefficient kl I EOI indicating its characteristics is known, but if it has not been calibrated, data obtained in a calibration experiment regarding the flow rate F and the sensor output signal E should be used. It is sufficient to perform linear regression based on , use the regression equation as a conversion equation, and use the coefficient kl + Eol obtained from this. If the output signal of the flow rate sensor 16m is EI+the flow rate is F, then from the above, El=klF+Eot·'·(3). In addition, since the output signal of the flow rate sensor 16 & is normally a minute signal, it is necessary to convert this output signal E into the flowmeter output value v1 corresponding to the flow rate. This is done using the equation solved for vl. This conversion is performed by the signal processing circuit 16b of the flowmeter 16, but since an inherent error occurs in the conversion in the signal processing circuit 1'6b,
In general, Vs = ttl Et + tl−(
4) The relationship becomes as follows.

On the other hand, although the flow rate sensor 17m is unknown, there is a unique flow rate-sensor output signal conversion formula, which can be expressed as Ex = kg F + Eoz - (5). 2 and E to this coefficient. , is sensor-specific, so it is impossible to correct it. However, as in the flowmeter 16, the formula for converting the output signal E2 of the flow rate sensor 17m into the flowmeter output value V in the signal processing circuit 17b is Vs = μ2 E2 + l! -(6), but the conversion coefficients μ2 and ε2 at this time can be corrected.

Therefore, in the calibration mode, the characteristics of the flowmeter 17 are calibrated in the following manner using the characteristics of the flowmeter 16 as a reference.

The flow rate in the calibration mode is Fc, the flow rate sensors 16a and 17
The output signals of a are Ecl and Ee2, respectively, and the flowmeter 16
Assuming that the output values of
In the calibration mode, the same flow rate Fc is applied, so vc! -v
e weight, that is, from equations (4) and (6), μCI Ee
It must be 2+ε2-μIE(!1+ε璽. Therefore, μ.2 Ee2=μIEel+ε2=ε1, and the calculation unit 25 directly inputs Ecl and Ee2 under the control of the control unit 21 and calculates the value. and within the known output value conversion coefficients for flowmeter 16 and using 61, flowmeter 17
The output value conversion coefficients μBM and ε2 are calculated as follows.

μc2=μt Ec+/Eci”・(7)ε2−ε
1...(8) Then, the flowmeter output value V is determined from the sensor output signals El and E2 in the signal processing circuits 16b and 17b in the measurement mode.
, and the conversion formula to vl, Vl = fis El +
For t 1 - (4), ■2-μc2 E2+ε1=(μl Ec+/Eat
) Calibrate as E2+εt-' (9). For example, F.C.
= 500 m1m1 n, kt=o, o105
.

Eo+=0.12, μ,=95. εl=5.15+
To illustrate the case of Eo2-5.02, (3),
From equations (7) and (8), μc2=95X(0,010
5X500 + 0.12) 15.02 = 101.6235 ε, = -5.15, the conversion formula from the sensor output signal to the flowmeter output value in the signal processing circuits 16b and 17b in the measurement mode is Vl = 95 For XE, -5,15, it is calibrated as Vt=101.6235XE2-5.15.

As described above, in the calibration mode, the characteristics of the flowmeter 16 (μm r
Characteristics of the flowmeter 17 (μ
2. ε2) is calibrated. After this, the measurement mode is entered, and the measurement error in the measurement mode will be described below.

The flow rate of dialysate flowing through the flow rate sensor 16a in the measurement mode is F, the flow rate of dialysis waste flowing through the flow rate sensor 17a is Fo, the output voltages of the flow rate sensors 16a and 17a at that time are Ei l Eo, and the flow meter output value is Each Vl
, Vo, then from equations (3) and (5), E4 = +
F1 +Eo1 + E6 = 2F6 +Eo*,
The conversion formula to the flowmeter output value in the signal processing circuits 16b and 17b is Vi = μ from formulas (4) and (9), respectively.
IEi+εl...00 ■. −μc2 EO+εs −(11). Therefore, the measured value U of ultrafiltration rate. b is as follows.

Uob=Vo vl−μax(k2F□+E62)−μ
l(klF1+Eo+) −=2Fo−μ+ to μe2
)c+Ft+(μc 2 Evil−μtEot) −
(1) As mentioned in the previous calibration mode, μc2Ee2”
"μIEcl, so from equations (3) and (5), μcg(ksFc+Eo = μ' (kIFc+Eot
) Therefore μ(!2 FO2−μIE61= (μc2
k 2 Fc - klF'c), this formula can be written as (6
), the measured value of ultrafiltration rate U. b becomes as follows.

Uob=μe2 k2 FO−μ+kIFt (μc2
2Fc-μl k t Fc) ・=(1 Now, if the true value of the ultrafiltration rate is ure, then Ure is the dialysis fluid flow rate F. minus the dialysate flow rate Fl, which is as follows. .

Ure = Fo-Fl -H Therefore, the measurement error δ of the ultrafiltration amount is 64 from the formula (to)
Subtracting the formula, δ”Uob Ure=μc2 k 2 Fo−μtk+
F+ (2Fe-μIklFe in μc2) (FoFs) = μ02! (FOFc)-μ+kt(FI Fc)
(Fo Fi), and therefore the error rate Δ is as follows.

Δ=δ/Ure ”” (Uob Ure)/Ure
""[l"A'CF.p'c)-μ mountain (Fl-Fc)
-(Fo-PI))/(Fo-Ft)...α Now,
Considering the inlet flow rate Fl in the measurement mode with respect to the flow rate Fc in the calibration mode, in actual dialysis,
There is little change in dialysate flow rate. Even if there is a fluctuation in the flow rate, considering the long dialysis time of several hours or more, this will fluctuate around the central value F1, and the average value will be Fl.

Therefore, considering it as Fl-Fc, there is no problem in practical use.

Therefore, 0 → formula is Δ−μc2 to 21...a→ becomes.

By the way, from equations (7) and (5), So, by substituting these into the 0 → formula, we get the following.

Also, according to equation (4), μI Eel =Vcl−ε1, so the measurement error of the ultrafiltration amount is as follows.

=(1+α)(1-β)(1-γ)-1...0ηIn particular, 1+α=vcl/Fc1β=ε1/V e r, γ
=Eoz/Ee2, α, β, and γ are the error of the flowmeter 16 when the flow rate at the time of calibration is applied, the zero error rate with respect to the output value of the flowmeter 16, and the zero error with respect to the output signal of the flow rate sensor 17a, respectively. rate.

That is, the measurement error of the ultrafiltration rate depends only on the zero error rate for the flow meter 17 with respect to its sensor output signal.

Now, to explain the case of the previous example, from equations (3) and (4), “cl”95X(0,0105X500+
0.12)-5,15-5,15 =505. Since ε1==-5,15, β;--C0.
0102, 05 Ecz = 5.02, Eo2 is Eox = 0.2 by actually measuring the output value of the flow rate sensor 17g when the flow rate is set to zero.
4 is 0.24, so 71 =-=0.0478, so even if the error of the calibrated flowmeter 5.0216 is, for example, +5%, α = 0.05, so these values can be substituted into the (1 power formula). Then Δ=(1±0.
05)X(1+0.0.102)(1-0,0478)
-1=001, and the measurement error of the ultrafiltration rate is only +1 inch.

By the way, β and γ in Equation 94 are considered to be within ±3% in a normal flowmeter. Therefore, even if α=±0.05 using a flow meter 16 with an error of +5, from formula 04, (1-0,05) (1-0,03) (1-0,03)-
1≦Δ≦(1+0.05) (1+0.03) (1+0
．． 03)-1, that is, 10, 11≦∆≦0.11, and even in the worst case, the measurement error remains at ±11 degrees.

An error of this magnitude does not pose a practical problem when measuring minute flow rates such as ultrafiltration rate. As described above, by calibrating the characteristics of the flowmeter 17 using the characteristics of the flowmeter 16 as a reference in the calibration mode, and then switching to the measurement mode, two flowmeters having substantially the same characteristics can be calibrated. This is equivalent to measuring the amount of ultrafiltration using this method, and errors due to differences in flowmeter characteristics can be greatly suppressed.

In the measurement mode, Vi is the dialysate flow rate and V is the dialysate drainage flow rate. are calculated using the α0 and al) formulas, respectively, and the calculation unit 25 calculates ■. -Vi is calculated and the result is displayed on the display section 26 as the ultrafiltration amount.

When the ultraviolet excess measuring device according to the present invention is built into or placed alongside a dialysis machine and enters the preparation mode as a dialysis machine, the above-mentioned calibration mode is also automatically performed, and then the dialysis mode is entered. Only the measurement mode may be performed in the dialysis mode, or the calibration mode may be automatically performed periodically in the dialysis mode. Alternatively, if necessary, the calibration mode may be manually set to perform the above-described calibration, and then the measurement mode may be manually switched. When only the measurement mode is performed in the dialysis mode, the dialysis time is usually about several hours, so during the dialysis time of this length, the flow rate sensor 17a gets dirty due to the dialysis drainage fluid, and the sensor conversion becomes difficult. Coefficient J + E+)2
It is almost unthinkable that this would change. However, if the period between one dialysis and the next dialysis is long, water scale and the like may be attached. Therefore, by providing a calibration mode at the same time as the preparation mode or during periodic inspection, the flow rate sensor 17a is washed with clean dialysate.

FIG. 3 shows an embodiment of the invention using a microcomputer, and parts corresponding to those in FIG. 2 are given the same reference numerals. The central processing unit of the microcomputer 27 (hereinafter referred to as C
The PU (hereinafter referred to as PU) 28 performs various processes by decoding and executing programs stored in a read-only memory (hereinafter referred to as ROM) 29, and stores data required for the processing and data in the middle of processing as necessary. The data is stored in a readable and writable memory (hereinafter referred to as RAM) 31. CPU2
8 sends the valve control signal to the valve control circuit 3 via the input/output section 32.
3, and the output of the valve control circuit 33 causes the switching valve 22.2 to
In addition, through the input/output section 32, the flowmeter output values v1+V2 of the flowmeter 16.17 and the output signals of the flow rate sensors 16a and 17a in the calibration mode can be taken in, and further V2-v, is calculated, and the result is supplied to the display circuit 26a of the display unit 26, and the result is displayed on the display 26.
Display on b. The flow meter 16 is calibrated in advance, and the conversion formula between the sensor output signal E1 and the flow rate F is E1=kIF +Eo+ (linear regression is performed between the flow rate at the sample point and the sensor output signal, and the regression line ), the sensor output signal El and the flowmeter output value v1
The conversion formula v1-μIEI+ε1 is known, and the values of these coefficients kl, Eot, μl, ε1 are stored in the ROM
It is stored in 29.

In this embodiment, when activated, the switching valves 22 and 23 are both controlled by a program fixed in the ROM 29 so that $-a and 0 are connected, and the supply device (not shown) After passing through the flow rate sensor 161, the dialysate from the dialyzer 161 flows through the side path 24 to the flow rate sensor 17m without passing through the dialyzer 12. It is set to the tab calibration mode. In the calibration mode, the characteristics of the flowmeter 17 are calibrated in the following manner using the characteristics of the flowmeter 16 as a reference.

As in the previous example, the flow sensor 16 in calibration mode!
The output signals of L and 17a are Eol and Eas, respectively.
The output value conversion coefficient for μ of the flow meter 17 is μ. , as shown in the flowchart of FIG. 4, in step S1, the CPU 28 first inputs Eas+Eas and the output value conversion coefficients μ and ε of the flowmeter 16 serving as a reference. Next, step, μ at β8°. ,=μtE'c
Subtract μ0 from m/Eat. Then, in step S3, the output value conversion coefficients μ2 and ε in the measurement mode of the flowmeter 17 are set to μ and =μ, respectively. .

The calibration value of ε,=6 is stored in the RAM 31.

After processing this calibration mode, the CPU 28
According to the program in 29, the switching valves 22 and 23 are switched to connect ports a and b, respectively, and the measurement mode is entered. In measurement mode, sensor output signals El and E of flowmeters 16 and 17. are each signal processing circuit 1
6b and 17b, as in the previous embodiment, the output value conversion coefficients obtained in the calibration mode are used (10 and α are converted into flowmeter output values Vl and V, respectively. The data is input to the CPU 28. From this, Vo-Vi is further calculated, and the result is displayed as the ultrafiltration amount on the display 26b via the display circuit 26a.

As described above, according to the present invention, the error (α
) and the zero error rate (β) for the output value are within ±5% and ±3qI), respectively, and the zero error rate (γ) for the sensor output signal of the flowmeter 17 is within ±3ch, then the flowmeter 16 and 17 may not be of the same type,
For example, 16 may be an electromagnetic flowmeter and 17 may be an ultrasonic flowmeter.

In addition, if the standard flowmeter 16 is of high precision, for example, with the measurement error (α) and the zero error rate (β) for the output value within ±1%, the tolerance for the measurement error of the extreme p excess amount is For example, even if the range is ±5 inches, 1α1≦0.0
1. lβ1≦0.01゜1Δ1≦O;05 (, From the α0 formula, the allowable range of γ for the flowmeter 17 is -0,029≦γ≦0.031, so a normal flowmeter will do. Sewing meter 1
7. Even without using a particularly high-precision device, it is possible to measure the ultralacrimal volume with an error of ±5 inches. The accuracy of the flow meter 16 can be improved by using a microcomputer or the like or by means of nearing, so by doing so, the allowable range of error for the flow meter 17 can be further widened.

Note that the switching valves 22 , 23 and the side passage 24 may be omitted, and the same flow rate of dialysate may be passed through the dialyzer 12 to the flow meters 16 and 17 in the calibration mode. In this case, in the calibration mode, the pressure on the blood flow path side and the pressure on the dialysate flow path of the dialyzer 12 are made equal, and control is performed so that water can move from both sides. Also, in the calibration mode, other liquids may be passed through the flowmeters 16, 17 instead of dialysate.

<Effects> As described above, according to the present invention, by providing a calibration mode in addition to the normal measurement mode in measuring the amount of ultrafiltration, errors due to variations in flowmeters can be minimized,
High-precision measurement is possible without using a particularly high-precision flow meter, and the flow path of the flow rate sensor 17m exposed to the dialysis fluid can be cleaned with clean dialysis fluid. In addition, regarding the calibration of the flowmeter output value, only the flowmeter 16 for measuring the flow rate on the inlet side is required, and the effort for adjustment can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing this conventional ultrafiltration rate measuring device,
FIG. 2 is a block diagram showing an example of the ultrafiltration rate measuring device according to the present invention, FIG. 3 is a block diagram showing an example of the ultrafiltration rate measuring device of the present invention using a microcomputer, and FIG. is a flowchart showing an example of the operation of the apparatus shown in FIG. 3 in the calibration mode. 11: Liquid supply line, 12: Dialyzer, 13: Drainage line, 16.17: Flowmeter, 21: Control section, 2j, 23: Switching valve, 24: Side path, 25: Computing section, 27: Microcomputer . Patent applicant Taku Kusano, agent of Sanyo Electric Manufacturing Co., Ltd.

Claims (1)

[Claims] (1) The flow rate of the dialysate flowing into the dialyzer is measured with a first flowmeter, the flow rate of the dialysis fluid flowing out from the dialyzer is measured with a second flowmeter, and the flow rate of these dialysis fluids and the dialysate are measured. In the ultrafiltration measuring device that measures the difference between the flow rate of a mode switching means for switching to a calibration mode for performing calibration; and a mode switching means for switching to a calibration mode for performing calibration; and an output signal of each flowmeter obtained at that time when liquid is caused to flow at the same flow rate to the first flowmeter and the second flowmeter in the calibration mode; and calibrating means for calibrating the characteristics of the second flowmeter based on the characteristics of the first flowmeter using the characteristic values of the meter.