EP1859168B1 - Method and device for determining the effective delivery rate or for adjusting the speed of a peristaltic pump - Google Patents

Description

The invention relates to a method and a device for adjusting the speed of a peristaltic pump, is conveyed with the liquid in an elastic tubing.

For reasons of sterility, preferably peristaltic or occluding pumps are used in medical technology. Various types of peristaltic pumps are known. One of these types is the roller pump. All peristaltic pumps have in common that an elastic tubing is inserted into the pump, in which the liquid to be pumped flows.

A particular application of peristaltic pumps in medical technology are the known extracorporeal blood treatment devices, which include, for example, hemodialysis devices, hemofiltration devices, and hemodiafiltration devices.

High demands are placed on the delivery accuracy of peristaltic pumps in medical technology, for example in extracorporeal blood treatment devices. The disadvantage is that the effective delivery rate of a peristaltic pump, which actually occurs at a given nominal rotational speed of the pump, depends on a large number of factors. Therefore, it can not be concluded from the nominal speed of the pump easily on the effective flow rate.

One of the key factors that determines the delivery rate of a peristaltic pump is the characteristics of the tubing. In practice it turns out that a deformation of the elastic tube leads to a change in the delivery rate of the pump.

The DE 197 47 254 C2 describes a method for noninvasive internal pressure measurement in elastic tubing. The document indicates that the properties of the tubing change over time.

From the US 6,691,047 For example, there is known a method for calibrating a peristaltic pump for an extracorporeal blood treatment device, wherein before the start of the blood treatment, the pressure in the tubing upstream of the pump is measured in order to make a prediction about the pressure upstream of the pump in the course of the treatment. In this case, the pump is calibrated at a pressure which corresponds to the mean value of the pre-measured pressure.

The US 4,715,786 describes a method for calibrating a peristaltic pump, but without taking into account a dependence of the delivery rate on time.

The WO 99/23386 describes a method for controlling the speed of peristaltic pumps in response to the pressure in the tubing upstream of the pump. The control is based on the physical characteristics of the tubing and the pump, but without again considering the time dependency.

From the US 5,733,257 a calibration method for peristaltic pumps is known in which the dependence of the delivery rate is negated by the time that the calibration takes place only after a predetermined period of time. It is assumed that the delivery rate does not change with time after this time has elapsed.

Also in the EP 0 513 421 A1 described method for determining the blood flow during extracorporeal blood treatment does not take into account the change over time of the delivery rate with the duration of the pump.

From the US 2005/0043665 A1 For example, a method and apparatus for determining the effective delivery rate of a peristaltic blood pump of an extracorporeal blood treatment device is known. The calculation of the effective delivery rate is based on the nominal speed of the pump and the pressure in the tubing upstream of the pump as a function of the running time of the pump. After determining the effective delivery rate, an adjustment of the nominal speed of the pump to the desired delivery rate can be made.

The invention has for its object to provide a method and apparatus for adjusting the speed of a peristaltic pump with high accuracy in order to adjust the effective delivery rate to the desired delivery rate can.

The solution of these objects is achieved according to the invention with the features specified in the claims 1 and 9. Advantageous embodiments of the invention are the subject of the dependent claims.

The inventive method and the inventive device for adjusting the speed of a peristaltic pump, is promoted with the liquid in an elastic hose, characterized by the fact that the

Adjustment of the effective delivery rate of the pump to the desired delivery rate based not only on the nominal speed of the pump and the pressure in the tubing upstream of the pump, but also depending on the running time of the pump.

In principle, it is possible to determine the expected effective delivery rate at a nominal rotational speed of the pump, wherein the effective delivery rate can be compared with the desired delivery rate. Since the effective delivery rate is likely to be lower than the desired delivery rate, the speed of the pump is increased until the effective delivery rate equals the desired delivery rate. A comparison between setpoint and actual value is possible with the method according to the invention and the device according to the invention for determining the effective delivery rate, without the effective delivery rate being measured.

In the invention, the equalization of the effective delivery rate of the pump to the desired delivery rate takes place initially in an initial compensation step. It is assumed that after carrying out this compensation step, the effective delivery rate largely corresponds to the desired delivery rate. After carrying out the initial compensation step, the remaining deviation of the delivery rate of the pump is then preferably compensated. The control of the pump is preferably carried out in continuous iterative compensation steps.

In the initial compensation step, a new speed is calculated by multiplying the nominal speed of the pump set before the compensation step by a correction factor, which operates the pump to match the effective delivery rate to the desired delivery rate.

To determine the correction factor, the pump is preferably operated at a predetermined speed, wherein the pressure in the tubing upstream of the pump is measured, which is at the predetermined speed established. The predetermined speed with which the pump is operated to determine the pressure in the hose line can be easily calculated according to an equation.

From the measured pressure, which is established upstream of the pump in the hose at the predetermined speed, the correction factor is preferably calculated according to an equation in addition to the pressure in the tubing upstream of the pump, one or more parameters are received, the relative decrease of Feed rate of the pump running time and one or more parameters, which describe the relative decrease of the delivery rate with the negative pressure in the tubing upstream of the pump.

The equation describing the relationship between the pressure in the tubing upstream of the pump and the correction factor can basically be solved in real time. Preferably, however, the individual pairs of values of pressure and correction factor are stored in a memory, so that the access to the data in real time is possible, but without having to solve the equation. As a result, the hardware and software costs for the determination of the correction factor can be reduced.

The initial compensation step takes place after starting the pump or setting a new set delivery rate. In further compensation steps deviations of the effective delivery rate of the pump from the desired delivery rate are continuously compensated. The essential correction in the initial compensation step is achieved. In the following rule, only minor deviations are generally eliminated.

When controlling the delivery rate of the pump, a maximum speed or delivery rate, for example relative to an initial starting value, can be taken into account as the upper limit value. Also, an upper limit may be provided for the amount of pressure upstream of the pump. If the individual sizes reach the upper limits, this can be used as an indication that the effective delivery rate can no longer be adjusted to the desired delivery rate. In this case, it is possible to give an optical and / or audible alarm, which indicates the user to the delivery rate deviation.

The regulation basically only needs to be carried out if the amount of the delivery rate deviation is above a predetermined lower limit. For example, with a delivery rate variance of less than one percent, further adjustment of the effective to the desired delivery rate is generally not required.

Advantageous embodiments provide that the predetermined stroke volume of the pump and the individual parameters for determining the correction factor for different tube systems are provided so that the corresponding stroke volume and the associated parameters can be predetermined by selection of the tube system.

In addition, the invention relates to a blood treatment device with a device for adjusting the speed of the peristaltic pump in order to promote the liquid in an elastic tubing with a desired delivery rate exactly.

In the following, various embodiments of the invention will be explained in more detail with reference to the drawings.

Figur 1

eine stark vereinfachte schematische Darstellung einer extrakorporalen Blutbehandlungsvorrichtung zusammen mit einer Vorrichtung zur Bestimmung der effektiven Förderrate der peristaltischen Pumpe der Blutbehandlungsvorrichtung und der erfindungsgemäßen Vorrichtung zur Einstellung der Drehzahl der Pumpe, um die Flüssigkeit mit einer gewünschten Förderrate zu fördern,

Figur 2

die effektive Förderrate der Pumpe in Abhängigkeit von dem Druck stromauf der Pumpe für verschiedene Förderraten und

Figur 3

die Abhängigkeit der effektiven Förderrate der Pumpe von dem Druck stromauf der Pumpe für verschiedene Drehzahlen der Pumpen.

Show it:

FIG. 1

a highly simplified schematic representation of an extracorporeal blood treatment device together with a device for determining the effective delivery rate of the peristaltic pump of the blood treatment device and the A device according to the invention for adjusting the rotational speed of the pump in order to convey the fluid at a desired delivery rate.

FIG. 2

the effective flow rate of the pump as a function of the pressure upstream of the pump for different flow rates and

FIG. 3

the dependence of the effective delivery rate of the pump on the pressure upstream of the pump for different speeds of the pump.

FIG. 1 shows in a highly simplified schematic representation of the essential components of an extracorporeal blood treatment device, such as a hemodialysis device, which has an extracorporeal blood circuit 1 and a dialysis fluid circuit 2. From a dialyzing fluid source 3 dialysis fluid flows through a dialysis fluid supply line 4 into a dialysis fluid chamber 5 of a dialyzer 8 divided by a semipermeable membrane 6 into the dialyzing fluid chamber 5 and a blood chamber 7, while dialyzing fluid from the dialyzer fluid chamber 5 of the dialyzer 8 flows through an outlet 10 to a dialysis fluid discharge line 9 , In the dialysis fluid discharge line 9, a dialysis fluid pump 11 is arranged.

The patient's blood flows via a blood supply line 12 into the blood chamber 7 and out of the blood chamber 7 of the dialyzer 8 via a blood discharge line 13 back to the patient. In the blood supply line 12, a blood pump 14 is arranged. Both the dialysis fluid pump 11 and the blood pump 14 are peristaltic pumps, in particular roller pumps. The blood supply and discharge lines 12, 13 and the dialysis fluid supply and discharge lines 4, 9 may be elastic plastic tubing, which are provided on the blood side as disposable for single use and inserted into the pumps. But it is also possible that
the lines are part of a cassette-like module from which the hose-side pumping segment protrudes in a loop shape.

The blood treatment device has a control unit 15, which is connected via control lines 16, 17 to the blood pump 14 or the dialysis fluid pump 11. The dialysis device furthermore has a computer unit 18, which communicates with the control unit 15 via a data line 19.

The hemodialysis apparatus also has other components which are generally known to the person skilled in the art and are not shown for the sake of clarity.

An apparatus and a method for determining the effective delivery rate of the blood pump 14 and adjusting the speed of the blood pump will be described in detail below. Corresponding devices may also be provided for the dialysis fluid pump 11.

The invention is based on the fact that the properties of the blood pump 14 with the associated tubing 12, which is inserted in the blood pump, are described as follows.

mit n

Rotordrehzahl der Blutpumpe [1/min],

V_S

Schlagvolumen bei einer Umdrehung der Blutpumpe [ml].

The effective blood flow Q _b, the blood pump 14 is calculated according to the following equation: $$Q_{b.\mathit{is}}=n*V_S$$

with n

Rotor speed of the blood pump [1 / min],

V _S

Stroke volume during one revolution of the blood pump [ml].

mit r

mechanische Abmessungen und Toleranzen der Blutpumpe [mm],

t

Laufzeit der Blutpumpe [h],

P_art

Unterdruck am Eingang der Blutpumpe [mmHg].

It is assumed that the stroke volume V _{S of} the blood pump 14 is a function of the mechanical dimensions r [mm] of the blood pump and of the blood pump Tube, the transit time t [h] of the blood pump and the pressure P _art [mmHg] in the blood supply line 12 upstream of the blood pump is: $$V_S=V_S\left(r,t,P_{\mathit{kind}}\right)$$

with r

mechanical dimensions and tolerances of the blood pump [mm],

t

Duration of the blood pump [h],

P _art

Vacuum at the inlet of the blood pump [mmHg].

In practice, in addition to the running time of the pump in particular their speed or cycle number of interest, which is directly proportional to the stress of the pump segment and thus responsible for the plastic behavior of the hose. However, this difference is less relevant for a constant delivery rate. However, if the funding rate is changed at different times, this can have an impact. Therefore, the variable t may be not only the running time but a parameter uniquely related thereto, for example, the accumulated speed of the pump. Thus, instead of the running time of the pump, the number of revolutions of the pump to be determined, for example, with a Hall sensor can be brought to the fore.

mit V_{S, 0} (r)

Schlagvolumen [ml] nach einer vorgegebenen Vorlaufzeit t₀ bei Nulldruck am Eingang der Blutpumpe,

a₁

Parameter [%/h], der die relative Abnahme der Förderrate mit der Laufzeit beschreibt,

b₁, b₂

Parameter [%/mmHg²], die die relative Abnahme der Förderrate mit dem arteriellen Unterdruck beschreiben.

The stroke volume of the blood pump as a function of the pressure P _art upstream of the pump in the hose line 12 and the running time t of the pump is described by the following equation: $$V_S=V_{S.0}\left(r\right)*\left(1-a_1*t\right)*\left(1-{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}}-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*{\mathrm{<figure-callout\; id="2"\; label="P\; kind"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_{\mathit{kind}}^{\mathit{}}\right)$$

with V _{S, 0} (r)

Stroke volume [ml] after a given lead time t ₀ at zero pressure at the entrance of the blood pump,

a ₁

Parameter [% / h], which describes the relative decrease of the delivery rate with the transit time,

b ₁ , b ₂

Parameters [% / mmHg ² ], which describe the relative decrease of the delivery rate with the arterial vacuum.

The predetermined stroke volume V _{S, 0} (r) [ml] after a predetermined lead time t _{0 of} the blood pump of, for example, 5 min at a negative pressure at the inlet of the pump of 0 is determined by the mechanical dimensions of the pump and the hose.

Since many types of hoses show a deviation from the linear time behavior according to equation (3), which is negligible after a few minutes of running time, it has proved useful to determine the predetermined stroke volumes V _{S, 0} (r) for this time. Due to the short lead time, the deviation of the actual pumping rate for this period is also negligible. In principle, however, it is also possible to specify predetermined stroke volumes V _{S, 0} (r) without pre-emergence effects, if this is not necessary due to the functional temporal relationship of the correction factor used.

The parameter a ₁ describes the relative decrease of the delivery rate of the pump with the transit time t, while the parameters b1 and b2 describe the relative decrease of the delivery rate with the negative pressure. The predetermined stroke volume and the individual parameters are characteristic variables for the blood pump used together with the hose line, which are determined in experiments and provided to the user.

The nominal delivery rate (blood flow) Q _{b, 0} [ml / min] after the predetermined running time of, for example, 5 min at zero pressure at the inlet of the pump is given by the following equation: $${\mathrm{<figure-callout\; id="0"\; label="Q\; b"\; filenames="imgf0002.png"\; state="\{\{state\}\}">Q\; </figure-callout>}}_b=n_{\mathit{old}}*V_{S.0}\left(r\right)$$

The effective delivery rate Q _{b, is} (blood flow) of the blood pump, which is to be expected when the pump is operated at the speed n, is given by the following equation: $$Q_{b.\mathit{is}}=n*V_{S.0}\left(r\right)*\left(1-a_1*t\right)*\left(1-{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}}-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*{\mathrm{<figure-callout\; id="2"\; label="P\; kind"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_{\mathit{kind}}^{\mathit{}}\right)$$

FIG. 2 shows the dependence of the effective delivery rate Q _{b, is} the pressure upstream of the blood pump for different delivery rates Q _{b, t} . It can be clearly seen that the delivery rate decreases with increasing arterial negative pressure. The absolute decrease is the greater, the higher the delivery rate (blood flow).

The device for determining the effective delivery rate of the blood pump 14 has means for measuring the pressure in the tubing 12 upstream of the blood pump 14 in the form of a pressure sensor 20, which is present in the known blood treatment devices anyway. The pressure sensor 20 is connected to the control unit 15 via a data line 21. In addition, means for determining the nominal speed of the blood pump 14 are provided, which are part of the control unit 15 of the dialysis apparatus insofar as the control unit 15 sets a certain speed for the blood pump 14. The same can apply to the dialysis fluid pump 11.

When the control unit 15 for the blood pump 14 sets a certain speed n, the blood pump delivers the blood at an effective delivery rate Q _b, (blood flow). The arithmetic unit 18 has the measured value of the arterial negative pressure from the pressure sensor 20 and the rotational speed n of the blood pump 14 from the control unit 15. Furthermore, the arithmetic unit has the parameters a1, b1 and b2 as well as the stroke volume V _{s, 0 (r)} . These empirically determined variables are stored in a memory 22, which is connected to the arithmetic unit 18 via a data line 23.

According to equation (5), the arithmetic unit 18 calculates the effective delivery rate Q _b , _is (blood flow), which adjusts itself at the predetermined speed n of the blood pump 14. Since it is to be expected that the effective delivery rate is smaller than that desired delivery rate, increases the control unit 15 as long as the speed n of the blood pump 14 to the effective delivery rate of the desired delivery rate Q _{b, should} correspond.

The device according to the invention and the method according to the invention for matching the effective delivery rate of the blood pump to the desired delivery rate by adjusting the rotational speed of the pump will be described in detail below.

The control of the speed of the blood pump begins with an initial compensation step, which can be carried out immediately after the start of the pump. This is followed by another compensation, which can be continuous or iterative. If the nominal delivery rate is changed, the initial compensation step initially takes place again, but the parameter t is not reset. In this way, the time influence on the delivery rate can be taken into account even if the delivery rate changes.

berechnet wird.First, the control unit 15 controls the blood pump 14 at a predetermined speed, which in the arithmetic unit according to the following equation $$n_{\mathit{old}}=\frac{Q_{b.\mathit{should}}}{V_{S.0}\left(r\right)*\left(1-a_1*t\right)}$$

is calculated.

At the predetermined by the control unit speed n _old , the arterial vacuum P _{art, old} , which is measured with the pressure sensor 20.

FIG. 3 shows the delivery rate (blood flow) Q _b, the blood pump 14 is dependent on the arterial vacuum P _art . According to equation (5) results in the measured negative pressure P _{art, old is} the expected effective delivery rate Q _{b, is old} . The control unit 15 now increases the speed n in the initial compensation step in order to compensate for the delivery deviation.

mit x

Korrekturfaktor

Due to the new speed n _new , the arterial pressure of P _{art, old} on P _{art, changes again} . The pressure change ΔP _art is set in proportion to the speed change Δn. $$\frac{{\mathit{P}}_{\mathit{kind}.\mathit{New}}}{{\mathit{P}}_{\mathit{kind}.\mathit{old}}}=\frac{{\mathit{n}}_{\mathit{New}}}{{\mathit{n}}_{\mathit{old}}}=1+\frac{\mathrm{\Delta }\mathit{n}}{n_{\mathit{old}}}=x$$

with x

correction factor

In the new arterial negative pressure P _{art, new} results in the new stroke volume V _{S, new} : $$V_{S.\mathit{New}}=V_{S.0}\left(r\right)*\left(1-a_1*t\right)*\left(1-{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}.\mathit{New}}-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*P_{\mathit{kind}.\mathit{New}}^2\right)$$

With the new stroke volume V _{S, new} would be at the previous speed n _old the delivery rate Q _{b, is, zw} : $$Q_{b.\mathit{is}.\mathit{tw}}=n_{\mathit{old}}*V_{S.\mathit{New}}$$

wobei der neue Erwartungswert des Blutflusses gleich dem Sollwert Q_b,soll gesetzt wird. Damit folgt: $$\frac{{\mathit{Q}}_{\mathit{b},\mathit{soll}}}{{\mathit{Q}}_{\mathit{b},\mathit{ist},\mathit{zw}}}=\frac{{\mathit{n}}_{\mathit{neu}}*{\mathit{V}}_{\mathit{S},\mathit{neu}}}{{\mathit{n}}_{\mathit{alt}}*{\mathit{V}}_{\mathit{S},\mathit{neu}}}=\frac{{\mathit{n}}_{\mathit{neu}}}{{\mathit{n}}_{\mathit{alt}}}=\mathit{x}$$

The new expectation value of the blood flow Q _{b is, new} results from the new rotational speed n _new and the current stroke volume V _{s, new} with: $${\mathit{Q}}_{\mathit{b}.\mathit{is}.\mathit{New}}={\mathit{Q}}_{\mathit{b}.\mathit{should}}={\mathit{n}}_{\mathit{New}}*{\mathit{V}}_{\mathit{S}.\mathit{New}}$$

wherein the new expected value of the blood flow is set equal to the set point Q _{b, soll} . With that follows: $$\frac{{\mathit{Q}}_{\mathit{b}.\mathit{should}}}{{\mathit{Q}}_{\mathit{b}.\mathit{is}.\mathit{tw}}}=\frac{{\mathit{n}}_{\mathit{New}}*{\mathit{V}}_{\mathit{S}.\mathit{New}}}{{\mathit{n}}_{\mathit{old}}*{\mathit{V}}_{\mathit{S}.\mathit{New}}}=\frac{{\mathit{n}}_{\mathit{New}}}{{\mathit{n}}_{\mathit{old}}}=\mathit{x}$$

When equations (7), (8), (9) are used in equation (11), the following equation results: $$\frac{Q_{b.\mathit{should}}}{n_{\mathit{old}}*V_{S.0}\left(r\right)*\left(1-a_1*t\right)}=x-{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}.\mathit{old}}*x^2-{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*P_{\mathit{kind}.\mathit{old}}^2*x^3$$

According to equation (6), the left side of equation (12) gives the value 1 independent of the desired value Q _{b, soll} . Thus, the equation of determination for the correction factor x as a function of the arterial negative pressure P _art follows: $${\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*{\mathrm{<figure-callout\; id="2"\; label="P\; kind"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">P\; </figure-callout>}}_{\mathit{kind}}^{\mathit{}}*x^3+{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}}*x^2-\mathrm{<figure-callout\; id="1"\; label="x\; +"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">x\; </figure-callout>}+1=0$$

The arithmetic unit 18 calculates the correction factor x from the arterial negative pressure P _{art determined} according to the equation (13) at the predetermined rotational speed n _alt . After determining the correction factor x, the arithmetic unit 18 calculated by multiplying the predetermined by the control unit 15 speed n _old by the correction factor x according to equation (11) the rotational speed n _new, the approximation of the effective feed rate O _{b, is} (effective blood flow) to the desired delivery rate O _{b, should} (blood flow) is set by the control unit 15.

Since the solution of the equation (13) during the term is very complex, provides an alternative embodiment of the invention to store the relationship between the arterial vacuum P _art and the correction factor x in a look-up table, which is set up in advance and stored in the memory 22 becomes. In this embodiment, the arithmetic unit 18 takes over the correction factor x belonging to the determined arterial negative pressure P _art directly from the memory 22, without solving the equation (13) in real time.

FIG. 3 shows that under the specification of the new speed n _new, a new arterial vacuum P _{art, neu} , in which the effective delivery rate of the blood pump Q _{b, is new} (blood flow) equal to the desired delivery rate Q _{b, soll} (blood flow).

• Während der initiale Kompensationsschritt nur nach dem Anlaufen der Blutpumpe ohne Kompensation durchgeführt werden kann, ist Gleichung (6) nach dem initialen Kompensationsschritt nicht mehr erfüllt, und der Korrekturfaktor x wird vom Verhältnis der gewünschten Förderrate Q_b,soll (Blutfluss) zur aktuellen Drehzahl n_art abhängig.

With the transit time t of the blood pump, the desired value will deviate from the actual value without further compensation. Therefore, the device according to the invention provides for continuous regulation of the rotational speed of the pump 14 by means of further compensation steps. First, the theoretical fundamentals of continuous control are described:

• While the initial compensation step can only be performed after the blood pump has started up without compensation, equation (6) is no longer satisfied after the initial compensation step, and the correction factor x becomes the ratio of the desired delivery rate Q _b (blood flow) to the current speed n _art dependent.

Equation (12) is returned to equation (13) by defining for the left side of equation (12): $$q=\frac{Q_{b.\mathit{should}}}{n_{\mathit{old}}*V_{S.0}\left(r\right)*\left(1-a_1*t\right)}$$

mit P_art,r = q*P_art Gleichung (15a) und x_r = x/q Gleichung (15b)Dividing equation (12) by equation (14) yields the following equation, which is formally identical to equation (13): $${\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_2*P_{\mathit{kind}.\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">r</figure-callout>}}^2*{\mathrm{<figure-callout\; id="3"\; label="x\; r"\; filenames="imgf0001.png"\; state="\{\{state\}\}">x\; </figure-callout>}}_r^{}+{\mathrm{<figure-callout\; id="1"\; label="b"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">b</figure-callout>}}_1*P_{\mathit{kind}.r}*x_r^2-x_r+1=0$$

with P _{art, r} = q * P _art equation (15a) and x _r = x / q equation (15b)

In order to be able to apply the table stored in the memory 22, which according to equation (13) in each case assigns a correction factor x to an arterial negative pressure P _art , a reduced correction factor x _r for a reduced arterial negative pressure P _{art, r is} determined. For this purpose, the arithmetic unit 18 first calculates the ratio q between the reduced correction factor x _r and the correction factor x according to equation (14). Here is the speed n _old after the initial compensation step of the control unit 15 currently specified speed. By multiplying the measured with the pressure sensor 20 arterial negative pressure P _art with the factor q calculates the arithmetic unit according to equation (15a) the reduced arterial pressure P _{art, r} . Then, the arithmetic unit of the table stored in the memory 22 takes the value of the reduced correction factor x _{r associated with} the reduced arterial negative pressure P _{art, r} . After the reduced correction factor is determined x _r, and the factor q is calculated, the computing unit 18, the speed to be set by the control unit 15 n from _new: $${\mathrm{n}}_{\mathrm{New}}={\mathrm{x}}_{\mathrm{r}}*{\mathrm{n}}_{\mathrm{old}}$$

The control unit 15 sets the new speed n _new , so that the actual value of the delivery rate is readjusted to the desired value. Is calculated will be followed by the next iterative compensation step, again initially the factor q in now given by the control unit 15 speed n _old, n the particular in the previous compensation step new speed _newly corresponds.

The substantial correction is achieved in the initial compensation step. Therefore, in principle, the following regulation could also be dispensed with. In continuous control, only minor deviations are usually eliminated, with the amount of maximum change per iteration being limited to 2% for arterial vacuum ≤ 150 mmHg and 4% for arterial vacuum ≥ 150 mmHg.

Claims (17)

1. Method for adjusting the speed of a peristaltic pump that conveys fluid in a flexible hose line, comprising the following method steps:

   determining the pressure in the hose line upstream of the pump and the nominal speed of the pump, and

   adjusting the nominal speed of the pump on the basis of the pressure in the hose line upstream of the pump depending on the running time of the pump, such that the actual conveyance rate corresponds to the desired conveyance rate,

   characterised in that,

   in order to determine a correction factor x, the pump is operated at a predetermined speed n_alt, the pressure that arises at the predetermined speed in the hose line upstream of the pump being measured,

   a speed n_neu is calculated by multiplying the speed n_alt of the pump by a correction factor x, the pump is operated at the calculated speed n_neu such that, in an initial compensation step, the actual conveyance rate Q_b,ist of the pump is matched to the desired conveyance rate Q_b,soll, and

   after the initial compensation step, the conveyance rate of the pump is regulated.
2. Method according to claim 1, characterised in that the predetermined speed n_alt at which the pump is operated in order to determine the pressure P_art in the hose line is calculated in accordance with the following equation: $$n_{\mathit{alt}}=\frac{Q_{b,\mathit{soll}}}{V_{S,0}\left(r\right)*\left(1-a_1*t\right)}$$

   

   where

   V_S,0(r) is the cardiac output [ml] after a given running time at atmospheric pressure at the inlet of the blood pump,

   a₁ is a parameter [%/h] that describes the relative decrease in the conveyance rate with respect to the running time t.
3. Method according to claim 2, characterised in that the correction factor x is determined from the pressure P_art that arises at the predetermined speed n_alt in the hose line upstream of the pump, in accordance with the following equation: $$b_2*P_{\mathit{art}}^2*x^3+b_1*P_{\mathit{art}}*x^2-x+1=0$$

   
4. Method according to any of claims 1 to 5, characterised in that, in a further compensation step, a speed n_neu is calculated by multiplying the nominal speed n_alt of the pump adjusted after the first compensation step by a correction factor x in order to regulate the conveyance rate of the pump, at which speed the pump is operated in order to match the actual conveyance rate of the pump to the desired conveyance rate.
5. Method according to claim 4, characterised in that, in order to determine the correction factor x, the ratio q is determined from the correction factor x calculated in the further compensation step and from a reduced correction factor x_r, in accordance with the following equation: $$q=\frac{Q_{b,\mathit{soll}}}{n_{\mathit{alt}}*V_{S,0}\left(r\right)*\left(1-a_1*t\right)}=\mathrm{x}/{\mathrm{x}}_{\mathrm{r}}$$

   
6. Method according to claim 5, characterised in that a reduced pressure P_art,r in the hose line upstream of the pump is calculated by multiplying the pressure measured in the hose line upstream of the pump by the ratio q of correction factor x to reduced correction factor x_r, the reduced correction factor x_r being calculated from the reduced pressure P_art,r in accordance with the following equation: $$b_2*P_{\mathit{art},r}^2*x_r^3+b_1*P_{\mathit{art},r}*x_r^2-x_r+1=0$$

   
7. Method according to claim 6, characterised in that the correction factor x is calculated by multiplying the reduced correction factor x_r by the ratio q of correction factor x to reduced correction factor x_r.
8. Method according to any of claims 4 to 7, characterised in that the conveyance rate of the pump is continually regulated in consecutive iterative compensation steps.
9. Apparatus for adjusting the speed of a peristaltic pump that conveys a fluid in a flexible hose line, comprising
   means (20) for determining the pressure in the hose line upstream of the pump and the nominal speed of the pump, and
   means for adjusting the nominal speed of the pump on the basis of the pressure in the hose line upstream of the pump depending on the running time of the pump, such that the actual conveyance rate corresponds to the desired conveyance rate of the pump,
   characterised in that an arithmetic unit (18) is provided and designed such that,
   in order to determine a correction factor x, the pump is operated at a predetermined speed n_alt, the pressure that arises at the predetermined speed in the hose line upstream of the pump being measured,
   a speed n_neu is calculated by multiplying the speed n_alt of the pump by a correction factor x, the pump is operated at the calculated speed n_neu such that, in an initial compensation step, the actual conveyance rate Q_b,ist of the pump is matched to the desired conveyance rate Q_b,soll, and
   after the initial compensation step, the conveyance rate of the pump is regulated.
10. Apparatus according to claim 9, characterised in that the arithmetic unit (18) is designed such that the predetermined speed n_alt at which the pump is operated in order to determine the arterial pressure P_art in the hose line is calculated in accordance with the following equation: $$n_{\mathit{alt}}=\frac{Q_{b,\mathit{soll}}}{V_{S,0}\left(r\right)*\left(1-a_1*t\right)}$$

    

    where

    V_S,0(r) is the cardiac output [ml] after a particular running time at atmospheric pressure at the inlet of the blood pump,

    a₁ is a parameter [%/h] that describes the relative decrease in the conveyance rate with respect to the running time t.
11. Apparatus according to claim 10, characterised in that the arithmetic unit (18) is designed such that the correction factor x is determined from the pressure P_art that arises at the predetermined speed n_alt in the hose line upstream of the pump, in accordance with the following equation: $$b_2*P_{\mathit{art}}^2*x^3+b_1*P_{\mathit{art}}*x^2-x+1=0$$

    
12. Apparatus according to any of claims 9 to 11, characterised in that the arithmetic unit (18) is designed such that, in a further compensation step, a speed n_neu is calculated by multiplying the nominal speed n_alt of the pump adjusted after the first compensation step by a correction factor x in order to regulate the conveyance rate of the pump, at which speed the pump is operated in order to match the actual conveyance rate of the pump to the desired conveyance rate.
13. Apparatus according to claim 12, characterised in that the arithmetic unit (18) is designed such that, in order to determine the correction factor x, the ratio q is determined from the correction factor x calculated in the compensation step and from a reduced correction factor x_r, in accordance with the following equation: $$q=\frac{Q_{b,\mathit{soll}}}{n_{\mathit{alt}}*V_{S,0}\left(r\right)*\left(1-a_1*t\right)}=\mathrm{x}/{\mathrm{x}}_{\mathrm{r}}$$

    
14. Apparatus according to claim 13, characterised in that the arithmetic unit (18) is designed such that a reduced pressure P_art,r in the hose line upstream of the pump is calculated by multiplying the pressure measured in the hose line upstream of the pump by the ratio q of correction factor x to reduced correction factor x_r, the reduced correction factor x_r being calculated from the reduced pressure P_art,r in accordance with the following equation: $$b_2*P_{\mathit{art},r}^2*x_r^3+b_1*P_{\mathit{art},r}*x_r^2-x_r+1=0$$

    
15. Apparatus according to claim 14, characterised in that the arithmetic unit (18) is designed such that the correction factor x_r is calculated by multiplying the reduced correction factor x_r by the ratio q of correction factor x to reduced correction factor x.
16. Apparatus according to any of claims 9 to 15, characterised in that the peristaltic pump is a roller pump or a finger pump.
17. Blood treatment apparatus comprising an apparatus according to any of claims 9 to 16.

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