JPH059009Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a hemodialysis device that uses a dialysis technique, such as a so-called artificial kidney, and is equipped with a function to control extreme excess.

"Prior Art" A conventional hemodialysis apparatus will be explained with reference to FIG. Blood is supplied from the patient's artery to a blood tube 1, and is sucked by a blood pump 2 into a chamber 3.
It is supplied to the dialyzer 4 via. This blood comes into contact with the dialyzer through a membrane within the dialyzer, and water and waste products in the blood move to the dialysate side. The water-removed blood is returned to the patient's artery from the dialyzer 4 via the chamber 5 and from the blood tube 7.

On the other hand, the dialysate supplied from the dialyzer supply unit 8 is supplied to the dialyzer 4 from the inlet line 12 via the constant flow valve 10 and the inlet valve 11 in this order. The dialysate that has taken in water and waste from the blood through the membrane in the dialyzer 4 is drained from the dialyzer 4 through an outlet line 13, an outlet valve 14, and a dialysate pump 15 to a drain. Inlet line 12 upstream of inlet valve 11
A bypass valve 16 is provided between the outlet line 13 and the outlet line 13 on the downstream side of the outlet valve 14 . Bypass valve 16 is normally closed.

A pressure sensor 23 is provided in the chamber 5,
The pressure on the blood circuit side is detected, and a pressure sensor 25 is provided in the outlet line 13 near the dialyzer 4,
The pressure on the dialysate circuit side is detected. A piston pump 17 is connected to the inlet line 12 close to the dialyzer 4 and a gear section 18 is provided adjacent to the piston pump 17 to reduce the speed of movement of the piston. Drive pulses having a pulse rate (number of pulses per unit time) set on the keyboard 21 are sent from the pulse generator 20 to the stepping motor 19.
is applied to The stepping motor 19 transmits rotation to the gear unit 18 according to the pulse rate. The gear portion 18 decelerates this rotation and moves the piston rod 17c.

The overpressure control unit 24 takes in data from the pressure sensors 23 and 25, and calculates the so-called overpressure (also called transmembrane pressure and often abbreviated as TMP) between the blood circuit side pressure P and the dialysis circuit side pressure Q. )
is calculated and compared with the preset control setting value,
The supply voltage of the dialysate pump 15 is controlled so as to eliminate this deviation.

The operation of the apparatus shown in FIG. 5 will be explained by mode.

(a) Initial setting mode The piston 17b of the piston pump 17 is set to an initial position (a position in contact with the end surface of the cylinder 17a on the inlet line 12 side). Inlet valve 11 and outlet valve 14 are opened and bypass valve 16 is closed. Using the keyboard 21, the ultra-ultraflow rate (the flow rate of water that moves from the blood to the dialyzer side through the membrane of the dialyzer) is set.

(b) Preparation mode The inlet valve 11, outlet valve 14 (both open), and bypass valve 16 (closed) remain in the previous mode, the blood pump 2 is turned on, and dialysis is started. The voltage supplied to the dialysate pump 15 via the overpressure control unit 24 is set, and the overpressure is set to a predetermined value (for example, 0 mm
Hg).

(c) Overpressure measurement mode The inlet valve 11 and outlet valve 14 are closed, the bypass valve 16 is opened, and the dialysate circuit centered on the dialyzer 5 is independent from the others with the inlet valve 11 and outlet valve 14 as boundaries. It is assumed that During this time, the piston pump 17
is turned on, negative pressure is applied to the dialysate circuit connected to it, and dialysate is sucked in at a flow rate approximately equal to the set ultra-overflow rate. This operation is similar to suction with a syringe, and the cylinder 17a
The piston 17b is moved while being in contact with the inner wall of the dialysate and sucks the dialysate. A piston rod 17c connected to the piston 17b protrudes from the center of the end face of the cylinder 17a and is guided into the gear portion 18, and the rod is moved while the thread formed by the rod engages with the gear of the gear portion 18. The gear of the gear unit 18 is driven by a stepping motor 19, and the motor 19 is driven by pulses from a pulse generator 20 (pulses at a pulse rate corresponding to the signal from the keyboard 21 where the ultra-high flow rate is set). Ru. The pressure value P on the blood circuit side detected by the pressure sensor 23 during suction by the piston pump 17 and the pressure value Q of the dialysate detected by the pressure sensor 25 are taken into the overpressure control unit 24, and the pressure difference P-Q, That is, the overpressure is calculated and stored in the memory as a control set value.

(d) Dialysis mode The inlet valve 11 and outlet valve 14 are opened, the bypass valve 16 is closed, and the dialysate is circulated through the dialyzer 4 again. At the same time, the detection values of each pressure sensor are taken in by the overpressure control unit 24. Then, the overpressure is calculated as before, this calculated overpressure is compared with the previously stored overpressure control set value, and the dialysate pump 15 is controlled to eliminate the deviation. In addition, the pulse generator 2 is activated by commands from the keyboard 21.
0, a reversal signal and a drive pulse are applied to the stepping motor 19, and the piston 17b is pushed back at a low speed by the reversal of the motor 19, and the dialysate sucked in earlier is gradually returned to the dialysis circuit.

In the above-mentioned dialysis mode, the dialysate pump 1 is operated to maintain the overpressure measured in the overpressure measurement mode, that is, the differential pressure that provides the set ultra-overflow rate.
5 is controlled, and the ultra-excess is carried out for a predetermined period of time.

"Problems to be Solved by the Invention" In the conventional device, the flow rate of dialysate sucked by the piston pump 17 in the overpressure measurement mode is affected by variations in the inner diameter of the cylinders constituting the piston pump. Therefore, the limit overflow rate in overpressure measurement mode deviates from the set value,
This will cause errors in overpressure measurements. In the subsequent dialysis mode, this measured value is used as the control setting value, so the ultra-ultraflow amount (integral value of the ultra-ultraflow amount) becomes a value that deviates from the setting value.

In addition, since the driving pulses applied to the stepping motor 19 are pulses with an approximate pulse rate obtained by dividing the system clock of the microcomputer system that controls the entire hemodialysis machine, the The error in the determined pulse rate cannot be ignored. Therefore, an error occurs in the extreme overflow rate in the overpressure measurement mode, resulting in the same problem as described above.

As described above, in the conventional technology, no measures have been taken against the above-mentioned TMP measurement error.

The purpose of this invention is to solve the above-mentioned problems of the conventional technology, which are caused by the above-mentioned errors caused by variations in the inner diameter of the cylinder of the piston pump (processing errors) and errors in the pulse rate given to the stepping motor of the piston pump. To provide an accurate hemodialysis device in which an error in a measured value in an overpressure measurement mode does not result in a control overpressure error in a subsequent dialysis mode, and furthermore, does not cause an error in an extreme excess amount in a dialysis mode. There is a particular thing.

``Means for Solving the Problems'' According to this invention, an overpressure measurement mode is created due to an error in the suction flow rate caused by an error in the pulse rate applied to the stepping motor of the piston pump and an error in the inner diameter of the cylinder of the piston pump. The hemodialysis apparatus is provided with a means for storing a correction coefficient for correcting a deviation in the measured value of and a means for correcting the measured value obtained in the overpressure measurement mode using the correction coefficient.

"Example" An example of this invention is shown in FIG. Components that are the same as those in FIG. 5 are given the same reference numerals, and redundant explanation will be omitted. In this example, a microcomputer is used in the hemodialysis machine, with a CPU (central processing unit) of 30
Measurement and control of overpressure are performed by decoding and executing a system program stored in a ROM (read-only memory) 31.

The operations in the initial setting mode and the preparation mode are the same as those described in the prior art, so their explanation will be omitted.

(a) Overpressure measurement mode The CPU 30 controls the inlet valve 11 and the outlet valve 14 to close and the bypass valve 16 to open via the /O (input/output circuit) 32 and driver 33. CPU30
reads the ultra-overflow data set in the setting switch 34, calculates the pulse rate (number of pulses per unit time) of the drive pulse to give that flow rate, and calculates an approximate value approximately equal to the calculated pulse rate. driver 35 at a pulse rate of
The stepping motor 19 is driven via the stepper motor 19. As a result, the pressure of the dialysate changes, but gradually reaches a stable state. Meanwhile, the CPU 30 uses the pressure sensor 25
The data Q (pressure of the dialysate) is sent to the A/D converter 36.
The data is captured every 0.1 seconds and stored in the RAM 37. Further, data P (pressure on the venous circuit side) of the pressure sensor 23 is similarly transmitted via the A/D converter 38.
It is stored in RAM37, and CPU30 stores it every 0.1 seconds.
Calculate TMP, store it in RAM 37, and use it for 10 seconds.
Calculate the moving average value of TMP and the standard deviation around it. As the pressure Q of the dialysate approaches a stable state, the standard deviation gradually decreases. When the CPU 30 detects that this standard deviation has become less than a predetermined value,
It is assumed that TMP has reached a stable state, and the moving average value at that point is used as the measured value of TMP in RAM 3.
Store in 7. Note that the timing at 0.1 second intervals is given by the timer 40.

The predetermined value of the standard deviation for determining a stable state is, for example, 2 mmHg, taking into account the pulsation caused by the influence of the blood pump.
It is said that

Pulse Rate of Piston Pump Drive Pulse A method for setting the pulse rate of the drive pulse applied to the stepping motor 19, which is necessary for the piston pump 17 to suck dialysate at a flow rate equal to the set ultra-overflow rate, will be described. As an example, set as follows.

Setting range of ultra-overflow UFR: 0.18~1.50
/hour, 0.01/hour step, (3000~25000
ml/min, 0.1667ml/min step) Step angle of pulse motor: 1.8 degrees/pulse (Number of pulses required for one rotation N: 360/1.8 = 200 pulses) Reduction ratio α of gear: 1/5 Piston rod screw Pitch p: 0.125cm Cylinder diameter: 3.6cm (Cross-sectional area S: 10.179
^cm2 ).

The relationship between the ultraviolet flow rate UFR (ml/min) and the piston moving speed v (cm/min) is as follows, if the cross-sectional area of the cylinder is S (cm ² ), then UFR=S×v (1) . The rotational speed n (rotations/min) of the screw of the piston rod is given by n=v/p (2) when the pitch of the screw is p (cm). The rotational speed m (revolutions/min) of the stepping motor is If α is the reduction ratio of
(seconds) is pr=(m/60)×N (4) where N is the number of pulses required to rotate the motor once. From equations (1) to (4), the relationship between the pulse rate pr (pulses/second) and the ultraviolet flow rate UFR (ml/min) is as follows: pr = (N/60Sαp) x UFR = 13.10 x UFR (5) Become. If UFR = 3-25 ml/min, pr = 39.30-327.5 pulses/sec.

However, in reality, instead of using the pulse rate pr determined in this way, an approximate pulse rate obtained by dividing the system clock of the microcomputer system that controls the entire hemodialysis machine is used. .

In this example, the clock of CPU30 is 4.9152/2
(MHz), and the frequency fc of the reference clock for the stepping motor is 9600, which is divided by 1/256.
It is assumed to be Hz. Therefore, the pulse rate pr found above
If the reference clock (frequency fc) is frequency-divided to obtain the following, the frequency division ratio γ is given by 1/γ=fc/pr=244.27 to 29.313 (6). (The reciprocal of the frequency division ratio is called the time constant.) In this way, the time constant 1/γ has many digits,
If the value is below the decimal point, frequency division becomes extremely complicated, so round off the decimal point and use a time constant or frequency division ratio approximating 1/γ'=244-29 (7). Therefore, the actual pulse rate pr' is pr'=fc/(1/γ')=39.34 to 331.0 (8) pulse seconds.

Regarding overpressure correction Assuming that there is no machining error in the inner diameter of the cylinder, the extreme overflow rate UFR' obtained using the approximate pulse rate pr' described above is UFR' = pr'/13.10 (5') . The relationship between the set extreme overflow rate UFR and the approximate extreme overflow rate UFR' actually achieved by suctioning the piston pump is as follows from equation (5) (5'): UFR = UFR' x pr/pr' = UFR′×β (9) Here, β is the correction coefficient, and β=pr/pr′=γ/γ′ (10). UF,
UF', the difference between them is ΔUF=UF'-UF=(UFR'-UFR) ×5×60=UFR(1/β-1)×5×60ml
(11) The figure shows the pulse rate pr, the approximate time constant 1/γ'=fc/pr', the 5-hour conversion value ΔUF of the error in the ultra-high overflow rate, and the correction coefficient β for each set ultra-high overflow rate UFR.

Since the limit overflow is approximately proportional to the overpressure,
The actually measured TMP′ was corrected as the overpressure measurement value in the overpressure measurement mode.

Use TMP=βTMP′ (12). This is because in the dialysis mode, this corrected overpressure is used as the control set value, and the error due to approximation of the time constant 1/γ and therefore the pulse rate pr is compensated for.

Effect of machining error on cylinder inner diameter Under the above setting conditions, assume that the actual inner diameter of the cylinder is 3.55 cm and there is a machining error of -0.05 cm. In this case, the cross-sectional area S′ is 9.898 cm ² ,
The ratio to the exact cross-sectional area is ξ=S′/S=9.898/10.179=0.9724 (13). Since the liquid flow rate sucked by the piston pump is proportional to the cross-sectional area, the actual suction flow rate, that is, the ultra-limit overflow rate, is UFR″=ξ×UFR (14). The error is ΔUFR″=UFR−UFR″=UFR(1−ξ) (15) (Actually, the error due to the approximate pulse rate is further superimposed.) Measured with an error of ΔUFR″ in the suction flow rate. The resulting overpressure deviates from the measured value under ideal conditions with no error in the suction flow rate.However, without taking any measures, this deviated overpressure was used as the overpressure control setting value in the next dialysis mode. Then, the error ΔUF of the ultraviolet amount occurring in the total time of overpressure measurement mode and dialysis mode (assumed to be 30 minutes) is calculated from equation (15) as follows: ΔUF = (UFR - UFR'') x 30 = UFR (
1-ξ)×30 = 16.667×(1-0.9724)×30=13.792ml(16). Therefore, if dialysis is performed for 5 hours,
The error will be approximately 10 times larger than this, so countermeasures must be considered.

As is clear from equation (5), when the cross-sectional area S of the cylinder is multiplied by ξ, the suction flow rate is the same as when ξ=1, that is, when there is no error in the cross-sectional area, that is, the set limit It can be seen that in order to obtain the overflow UFR, the pulse rate pr of the drive pulse should be corrected to pra=pr/ξ=(13.10/ξ)UFR (17). In other words, the cross-sectional area S of the cylinder is multiplied by ξ, and if this continues, the suction flow rate will be multiplied by ξ, so the pulse rate pr should be reduced by 1/ξ.
In other words, the piston was moved at a slower speed by lowering it twice as much.

If the frequency division ratio of the reference clock when using the corrected pulse rate pra above is γa, the time constant is 1/γa = fc/pra (6') Rounding off the decimal point of the time constant 1/γa. If the obtained approximate time constant is 1/γa′, then the approximate pulse rate when using this approximate time constant is
pra′ is pra′=fc/(1/γa′) (8′) If the approximate suction flow rate at that time is UFRa′, then from equation (17), pra′=(13.10/ξ)UFRa′ (17′) becomes. Approximate pulse rate from (8′), (17′)
The correction coefficient βa for using pra′ is βa=UFR/UFRa′=pra/pra′ (9′) From (6′) and (8′), βa=pra/pra′=γa/γa′ (10′) As the overpressure measurement value in the overpressure measurement mode, the actually measured overpressure TMPa′ is corrected by βa, and TMPa=βaTMPa′ (12′) is used. Note that the subscript a attached to each letter means that the influence of errors in the inner diameter of the piston has been corrected.

Figure 3 shows the setting limit overflow rate UFR = 0.18 to 1.50/hour (0.01
A part of the pulse rate pra, approximate time constant 1/γa', and correction coefficient βa for the step) is shown. The difference ΔUFa between the approximate extreme excess UFa' and the extreme excess UF without approximation error in the total dialysis time (5 hours) is: ΔUFa = UFa' - UF = (UFRa' - UFR) x 5 x 60 = UFR (1/βa-1)×5×60 (11′). ΔUFa is also shown in FIG.

Regarding the cylinder 17a of the piston pump,
Precisely measure its inner diameter in advance, and calculate the pulse rate pra' actually applied to the stepping motor 19 and the correction coefficient βa in that case from the above relational expression.
Approximate time constant 1/γa' and correction coefficient βa corresponding to the ultra-limit overflow rate of 0.18 to 1.50/hour (0.01/hour step) are stored in the ROM 31, and are read out as appropriate for correction processing.

FIG. 4 shows a flowchart of a program related to this correction process. This process is performed in an interrupt routine every 0.1 seconds. In this interrupt routine, other processes such as device control are also performed at the same time, but only the parts related to this process are shown.

In step 1, the CPU 30 reads the ultra-high overflow setting value UFR set by the setting switch 34 via the I/O 32 and stores it in the RAM 37. In step 2, the CPU 30 uses this setting value table (0.18
~1.1.50/hour is written in steps of 0.01/hour), the time constant 1/γa' table (for example, the third Figure 238
Values up to ~29 are written. ) is picked up and written to the RAM 37. For example, if the set limit overflow rate UFR is 0.60/hour, the corresponding time constant 1/γa'=71 is written. In step 3, the CPU 30 applies a pulse (pulse rate pra'=fc/(1/γa') obtained by dividing the system clock by this time constant to the stepping motor 19 via the /O 32 and the driver 35. In step 4, The CPU 30 judges whether the dialysate pressure Q is stable or not, and if it is stable, the current
The moving average value _TMP1 of TMP is stored in the RAM 37 (step 5). RAM in step 6 and step 1
In step 7, the corresponding correction coefficient is picked up from the table of correction coefficients βa in the ROM corresponding to the table of the extreme overflow setting value written in the table (in the previous example, the corresponding correction coefficient is 0.99628). This correction coefficient is multiplied by the previous TMP ₁ to obtain a correction TMP to be controlled in the next dialysis mode, and is stored in the RAM 37.

As is clear from the above explanation, the ROM 31 provides a correction coefficient for the deviation in the measured value of overpressure due to the suction amount caused by the error in the pulse rate applied to the stepping motor of the piston pump and the error in the inner diameter of the cylinder of the piston pump. The CPU 30, ROM 31, and RAM 37 constitute means for performing the same correction on the overpressure obtained in the overpressure measurement mode.

(b) Dialysis mode When TMP is measured in overpressure measurement mode and the measured value is set as the control setting value, CPU3
0 opens the inlet valve 11 and outlet valve 14, and the bus pass valve 1
6 is controlled to close. In addition, the CPU 30 uses the control setting value stored in the RAM 37 (a value obtained by applying a correction coefficient to the TMP obtained in the previous overmeasurement mode), the blood circuit side pressure P and the dialysate pressure Q taken in every 0.1 seconds.
The dialysate pump 15 is controlled via the driver 41 so as to eliminate the deviation by comparing the moving average value TMP ₁ of TMP calculated from .

The dialysis mode normally ends automatically 30 minutes after the start of the overpressure measurement mode, returns to the overpressure measurement mode, and repeats measurement and dialysis.

"Effects of the Invention" According to this invention, it is possible to accurately correct errors in TMP measurements caused by errors in the pulse rate applied to the stepping motor of the piston pump and errors in the machining of the inner diameter of the piston pump cylinder, which are the largest causes of errors in the measured TMP obtained in the overpressure measurement mode, and it is possible to obtain a hemodialysis device with an extremely small error in the extreme overpressure compared to conventional devices.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram showing one embodiment of the hemodialysis device according to this invention, and Fig. 2 shows the pulse rate pr approximate time for each set ultra-overflow rate UFR when there is no error in the cylinder inner diameter of the piston pump. 5-hour conversion value ΔUF of the error of the limit excess amount due to the use of constant 1/γ' and approximate time constant 1/γ'
Figure 3 shows the correspondence between the correction coefficient β and the pulse rate pra, approximate time constant 1/γa′, approximate time constant 1/ A diagram showing the correspondence between the 5-hour conversion value ΔUFa of the error of the limit excess amount due to the use of γa' and the correction coefficient βa. Figure 4 mainly shows the correction process in the interrupt processing routine in the overpressure measurement mode of the device in Figure 1. FIG. 5 is a block system diagram of a conventional hemodialysis apparatus.

Claims (1)

[Scope of Claim for Utility Model Registration] During dialysis, both the supply of dialyzer to the dialyzer and the discharge of dialysate from the dialyzer are stopped for a short time, and the above-mentioned dialysis is performed at a preset ultra-overflow rate using a piston pump. An overpressure measurement mode is provided in which the fluid is sucked and the overpressure (transmembrane pressure) at that time is measured, and the supply of dialysate to the dialyzer and the discharge of dialysate from the dialyzer are restarted, and after restarting. In a hemodialysis machine equipped with a dialysis mode in which dialysis is performed by controlling the dialysate pressure or the blood circuit side pressure so that the overpressure of the piston pump becomes equal to the measured value obtained in the overpressure measurement mode, means for storing a correction coefficient for correcting a deviation in the measured value of the overpressure due to an error in the suction flow rate caused by an error in the pulse rate applied to the stepping motor and an error in the inner diameter of the cylinder of the piston pump; A hemodialysis apparatus comprising means for correcting the measured value of the overpressure using the correction coefficient.