DEVICE FOR EXTRACORPOREAL BLOOD TREATMENT WITH GRAVIMETRIC BALANCING AND POSSIBILITY OF ULTRAFILTRATION

Abstract

A device for extracorporeal blood treatment, in particular a dialysis machine, including an internal fluidic system to which a blood treatment unit, in particular a dialyzer, can be connected, the internal fluidic system comprising at least one balancing chamber on the fresh flow side for balancing fresh treatment fluid flowing to the blood treatment unit and at least one balancing chamber on the used flow side for balancing used treatment fluid flowing off the blood treatment unit, wherein the device has a measuring device for gravimetric detection of treatment fluid in the balancing chamber on the fresh flow side and/or a measuring device for gravimetric detection of treatment fluid in the balancing chamber on the used flow side. A method of balancing treatment fluid in such a device.

Claims

1.-13. (canceled)

14. A device for extracorporeal blood treatment comprising: an internal fluidic system to which a blood treatment unit can be connected, wherein the internal fluidic system comprises a balancing chamber on a fresh flow side for balancing fresh treatment fluid flowing to the blood treatment unit and a balancing chamber on a used flow side for balancing used treatment fluid flowing off the blood treatment unit, at least one of a measuring device for gravimetric detection of treatment fluid in the balancing chamber on the fresh flow side or a measuring device for gravimetric detection of treatment fluid in the balancing chamber on the used flow side, wherein two balancing chambers are fluidically arranged in series on each of at least one of the fresh flow side or the used flow side of the treatment unit.

15. The device according to claim 14, wherein the measuring device comprises at least one of a balance or a force sensor to determine the mass of treatment fluid present in the balancing chamber.

16. The device according to claim 14, wherein the two balancing chambers are arranged on each of at least one of the fresh flow side or the used flow side of the treatment unit, wherein the two balancing chambers are fluidically arranged parallel.

17. The device according to claim 14, wherein a switchable shut-off valve is arranged in the internal fluidic system on each of at least one of the inflow side or the outflow side of the respective balancing chamber for at least one of controlling or regulating the inflow and the outflow of the treatment fluid to or from the respective balancing chamber.

18. The device according to claim 14, wherein at least one of the balancing chambers has a ventilation opening having a filter unit.

19. The device according to claim 14, wherein the internal fluidic system comprises a pump for pumping treatment fluid on the inflow side of the balancing chamber and on the outflow side of the balancing chamber.

20. The device according to claim 14, wherein the balancing chamber is configured as a piston-cylinder unit with the balancing chamber as a cylinder and a piston cooperating with the cylinder and accommodated therein.

21. The device according to claim 14, wherein a constriction in the flow cross-section is formed in the internal fluidic system upstream of the balancing chamber on the fresh flow side for generating a local negative pressure and degassing the treatment fluid.

22. The device for extracorporeal blood treatment, wherein the device is a dialysis machine and the blood treatment unit is a dialyzer.

23. A method of balancing treatment fluid in a device for extracorporeal blood treatment, comprising: balancing fresh treatment fluid flowing to a blood treatment unit through an internal fluidic system of the device with a balancing chamber on a fresh flow side of the internal fluidic system; balancing used treatment fluid flowing off the blood treatment unit with a balancing chamber on a used flow side of the internal fluidic system, and determining a deviation from a target balance or a misbalance by comparing the balance on the fresh flow side and the balance on the used flow side, wherein at least one of treatment fluid present in the balancing chamber on the fresh flow side or treatment fluid present in the balancing chamber on the used flow side is gravimetrically detected by a measuring device; wherein in a first phase fresh treatment fluid on the fresh flow side is conveyed into a first balancing chamber on the fresh flow side, whereas fresh treatment fluid from a second balancing chamber on the fresh flow side is conveyed to the treatment unit, and used treatment fluid on the used flow side is conveyed from the treatment unit into the first balancing chamber on the used flow side, whereas used treatment fluid is conveyed from a second balancing chamber on the used flow side to a drain of the device, and wherein in a second phase fresh treatment fluid on the fresh flow side is conveyed from the first balancing chamber on the fresh flow side into the second balancing chamber on the fresh flow side, whereas fresh treatment fluid from the second balancing chamber on the fresh flow side is conveyed to the treatment unit, and used treatment fluid on the used flow side is conveyed from the first balancing chamber on the used flow side into the second balancing chamber on the used flow side, whereas used treatment fluid is conveyed from the treatment unit into the first balancing chamber on the used flow side.

24. The method according to claim 23, wherein the treatment fluid present in the respective balancing chamber is continuously detected by the measuring device.

25. The method according to claim 24, wherein the treatment fluid present in the respective balancing chamber is continuously balanced.

26. The method according to claim 23, wherein an undesired deviation from the target balance or misbalance is compensated by generating an excess or reduced delivery of treatment fluid by a pump.

27. The method according to claim 23, wherein a pump is used to generate an excess or reduced delivery of treatment fluid such that ultrafiltration is affected.

28. The method according claim 23, wherein in the first phase fresh treatment fluid on the fresh flow side is conveyed into a first balancing chamber on the fresh flow side, whereas fresh treatment fluid is conveyed from a second balancing chamber on the fresh flow side to the treatment unit, and used treatment fluid on the used flow side is conveyed from the treatment unit into a first balancing chamber on the used flow side, whereas used treatment fluid is conveyed from a second balancing chamber on the used flow side to a drain of the device; and wherein in the second phase fresh treatment fluid on the fresh flow side is conveyed into the second balancing chamber on the fresh flow side, whereas fresh treatment fluid is conveyed from the first balancing chamber to the treatment unit, and used treatment fluid on the used flow side is conveyed from the treatment unit into the second balancing chamber on the used flow side, whereas used treatment fluid is conveyed from the first balancing chamber on the used flow side to a drain of the device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention is best understood from the following detailed description when read in connection with the accompanying drawings. Included in the drawings are the following figures:

[0042] FIG. 1 shows a diagram of a detail of a known device for extracorporeal blood treatment,

[0043] FIG. 2 shows a diagram of a section forming a balancing unit of a first embodiment of a device according to aspects of the invention for extracorporeal blood treatment,

[0044] FIG. 3 shows a diagram of a section forming a balancing unit of a second embodiment of a device according to aspects of the invention for extracorporeal blood treatment,

[0045] FIG. 4 shows a diagram of a section forming a balancing unit of a third embodiment of a device according to aspects of the invention for extracorporeal blood treatment,

[0046] FIG. 5 shows a diagram of a section forming a balancing unit of a fourth embodiment of a device according to aspects of the invention for extracorporeal blood treatment,

[0047] FIG. 6 shows a schematic perspective illustration of a balancing unit of an embodiment of a device according to aspects of the invention for extracorporeal blood treatment,

[0048] FIG. 7 shows a schematic perspective illustration of a balancing unit of an embodiment of a device according to aspects of the invention for extracorporeal blood treatment, and

[0049] FIG. 8 shows a schematic perspective illustration of a balancing unit of an embodiment of a device according to aspects of the invention for extracorporeal blood treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] FIG. 2 schematically shows a detail of a first embodiment of a device 1 according to aspects of the invention for extracorporeal blood treatment. In the present example, the device 1 is designed as dialysis machine 1 and comprises an internal fluidic system 2 to which a blood treatment unit 3, in this case a dialyzer 3, can be connected. The internal fluidic system 2 comprises a first balancing chamber 4 on the fresh flow side and a second balancing chamber 5 on the fresh flow side, each for balancing fresh treatment fluid flowing to the blood treatment unit 3. It also comprises a first balancing chamber 6 on the used flow side and a second balancing chamber 7 on the used flow side, each for balancing the used treatment fluid flowing off the blood treatment unit 3. The individual balancing chambers 4, 5, 6, 7 may be thermally insulated.

[0051] On the fresh flow side, the internal fluidic system 2 comprises an inflow line 8 connected to a (not shown) reservoir for fresh treatment fluid. A first fresh flow pump 9 is arranged in said inflow line in the internal fluidic system 2. Downstream of the pump 9, the line 8 is divided into a first fresh flow line branch 10 and a second fresh flow line branch 11, which are realized so as to be fluidically parallel to each other.

[0052] In the first fresh flow line branch 10, a valve 12 is arranged upstream of the first balancing chamber 4 on the fresh flow side and a valve 13 is arranged downstream of the first balancing chamber 4 on the fresh flow side. In the second fresh flow line branch 11, a valve 14 is arranged upstream of the second balancing chamber 5 on the fresh flow side and a valve 15 is arranged downstream of the second balancing chamber 5 on the fresh flow side. Downstream of the two valves 13, 15, the first fresh flow line branch 10 and the second fresh flow line branch 11 merge again to form a fresh flow line 16, in the further course of which a second fresh flow pump 17 is arranged and which is finally connected to the dialyzer 3 as treatment unit 3.

[0053] On the used flow side, the internal fluidic system 2 has a used flow line 18 which is fluidically connected to the dialyzer 3. A first used flow pump 19 is arranged in said used flow line. Downstream of the first used flow pump 19, the used flow line 18 is divided into a first used flow line branch 20 and a second used flow line branch 21, which are realized so as to be fluidically parallel to each other.

[0054] In the first used flow line branch 20, a valve 22 is arranged upstream of the first balancing chamber 6 on the used flow side and a valve 23 is arranged downstream of the first balancing chamber 6 on the used flow side. In the second used flow line branch 21, a valve 24 is arranged upstream of the second balancing chamber 7 on the used flow side and a valve 25 is arranged downstream of the second balancing chamber 7 on the used flow side. Downstream of the two valves 23, 25, the first used flow line branch 20 and the second used flow line branch 21 merge again to form a used flow line 26, in the further course of which a second used flow pump 27 is arranged and which is finally connected via a drain 28 to a (not shown) reservoir for used treatment fluid.

[0055] FIG. 2 also shows a part of an extracorporeal blood line 29 with indicated blood flow direction 30.

[0056] The device of FIG. 2 uses a total of four chambers 4, 5, 6 and 7, each of which may be thermally insulated. The switching rate of the chambers 4, 5, 6, 7 depends on the respective volumes of the chambers. As indicated in FIG. 2, the first fresh flow line 10, the second fresh flow line 11, the first used flow line branch 20 and the second used flow line branch 21 are connected to the respective chamber 4, 5, 6, 7 as close to the bottom as possible, so that as few dead spaces as possible remain within the respective chamber 4, 5, 6, 7 in which treatment fluid can accumulate.

[0057] Each of the four chambers 4, 5, 6, 7 has a ventilation opening 31, in the present case located at the top of the respective chamber 4, 5, 6, 7. The ventilation opening 31 serves to equalize the pressure when filling and emptying the respective chamber 4, 5, 6, 7. The ventilation opening 31 may be provided with a hydrophobic filter not shown in the Figure.

[0058] Below each individual chamber 4, 5, 6, 7 there is a measuring device 32 in the form of a scale or weighing device 32. Alternatively, the measuring device 32 can be arranged above the respective chamber 4, 5, 6, 7. The measuring device 32 is suitable and intended to continuously determine the weight of the respective chamber 4, 5, 6, 7 which are filled with more or less treatment fluid. The determined weights can be used to ascertain the mass flow of the pumps 9, 17, 19, 27. This is also used to determine the filling level of the chambers 4, 5, 6, 7.

[0059] To ensure a continuous flow of treatment fluid, its delivery is divided into two phases. At the beginning of a first phase, the chambers 4, 5, 6, 7 each having a respective filling volume of 100 ml are filled with the following masses of treatment fluid:

[0060] Chamber 4: 20 g, chamber 5: 80 g, chamber 6: 20 g, chamber 7: 80 g.

[0061] In the first phase, the device 1 is operated as follows:

[0062] Pump 9 fills chamber 4 through valve 12. Valve 12 is open, valve 13 is closed.

[0063] Pump 17 empties chamber 5 through valve 15. Valve 14 is closed, valve 15 is open.

[0064] Pump 19 fills chamber 6 through valve 22. Valve 23 is closed, valve 22 is open.

[0065] Pump 27 empties chamber 7 through valve 25. Valve 25 is open, valve 24 is closed.

[0066] The operation in the first phase continues until the chambers 4, 5, 6, 7 have reached a full or empty state.

[0067] At the beginning of a second phase, the chambers 4, 5, 6, 7 each having a respective filling volume of 100 ml are filled with the following masses of treatment fluid:

[0068] Chamber 4: 80 g, chamber 5: 20 g, chamber 6: 80 g, chamber 7: 20 g

[0069] In the second phase, the device 1 is operated as follows:

[0070] Pump 9 fills chamber 5 through valve 14. Valve 14 is open, valve 15 is closed.

[0071] Pump 17 empties chamber 4 through valve 13. Valve 12 is closed, valve 13 is open.

[0072] Pump 19 fills chamber 7 through valve 24. Valve 25 is closed, valve 24 is open.

[0073] Pump 27 empties chamber 6 through valve 23. Valve 23 is open, valve 22 is closed.

[0074] The operation in the second phase also continues until the chambers 4, 5, 6, 7 have reached a full or empty state.

[0075] As soon as the respective switching point (empty or full) of a chamber 4, 5, 6, 7 has been reached, the two valves belonging to a chamber 4, 5, 6, 7 close. As soon as all valves of all chambers 4, 5, 6, 7 are closed, the next phase begins, i.e. after the first phase the second phase, then again the first phase and so on.

[0076] The device of FIG. 2 can also be operated in an ultrafiltration mode within the scope of the invention, i.e. in such a way that liquid is withdrawn from a patient in a desired manner and to a desired degree. To generate ultrafiltration, the upper switching points of the chambers 4, 5, 6, 7 are defined differently and the fresh flow pump 17 and the used flow pump 19 are operated at different flow rates. In the present example, the fresh flow pump 17 runs at a flow rate of 500 g/min, which flow rate is determined by the measuring device. The used flow pump 19 is operated with a different delivery rate of 510 g/min, resulting in a total ultrafiltration of 600 g/h. At such conveying rates, the switching points 20 g and 80 g result for the chambers 4 and 5 (corresponding to a displacement of 60 g at 8.33 strokes per minute). For the chambers 6 and 7, the switching points are 20 g and 81.2 g (corresponding to a displacement of 61.2 g at 8.33 strokes per minute).

[0077] The fresh flow pump 9 and the used flow pump 27 must each be operated in such a way that the chambers fluidically connected to them are filled or emptied at least as quickly as the fresh flow pump 7 and the used flow pump 19 need in order to empty or fill the respectively other chamber fluidically connected to them.

[0078] In addition, the device of the embodiment of FIG. 2 is designed for degassing the treatment fluid. A constriction 33 or throttle 33 is arranged in the inflow line 8, which generates a dynamic negative pressure in the treatment fluid flowing through it. As a result of the negative pressure present there, any air dissolved in the treatment fluid separates in the form of air bubbles, which can then escape through the ventilation openings 31 in the balancing chamber 4 or 5. Air in the form of air bubbles that penetrate into the system, e.g. through leaks at the dialyzer couplings, can easily be removed from the internal fluidic system via the balancing chambers 6 and 7 with the device 1 according to aspects of the invention. Advantageously, a separate air separator for this purpose is not required for the device 1 of the invention.

[0079] A matching of the balancing chambers 4 and 5 or 6 and 7 is particularly easy with the device 1 according to aspects of the invention. Via the pumps 9, 17, 19, 27, different filling levels/filling quantities are set in the balancing chambers 4, 5, 6, 7, for example 20 g, 50 g and 80 g. Then the pumps 9, 17, 19, 27 are stopped and all chamber valves 12, 13, 14, 15 and 22, 23, 24, 25 are opened. Via the opened chamber valves 12, 13, 14, 15 and 22, 23, 24, 25, equal levels and thus equal filling quantities (weight) appear in the balancing chambers 4 and 5 or 6 and 7.

[0080] In addition, the balancing chambers 4 to 6 (or 4 to 7, 5 to 6, 5 to 7) can be easily matched as follows: Via the pumps 9, 17, 19, 27, the balancing chamber 4 is filled (e.g. with 80 g treatment fluid) and the balancing chamber 6 is emptied (e.g. to a quantity of 20 g treatment fluid). The treatment fluid is then pumped from the balancing chamber 4 into the balancing chamber 6. This can be done in a first variant with only one pump by bridging one of the pumps 17 and 19 with a bypass not shown in FIG. 2, so that the remaining pump 17 or 19 directly produces a flow between the balancing chambers 4 and 6. Alternatively, this can be done in a second variant with two pumps by operating the pumps 17 and 19 in such a way that both have the same delivery rate. For this purpose, for example, a pressure sensor not shown in FIG. 2 can be used between the two pumps 17 and 19. If the pumps 17 and 19 are then operated at such a speed that this pressure does not change, it is ensured that both pumps 17 and 19 convey the same amount of treatment fluid. After the lower level of 20 g treatment fluid has been reached in the balancing chamber 4, the weight of the treatment fluid in the balancing chamber 6 must have increased to the initial weight of the balancing chamber 4, i.e. 80 g in this case.

[0081] Finally, the device 1 according to aspects of the invention enables a simultaneous matching of all balancing chambers 4, 5, 6, 7. By integrating a short-circuit valve (not shown in FIG. 2) between e.g. the valves 14 and 15, the above described matching procedure can be carried out simultaneously for all balancing chambers 4, 5, 6, 7.

[0082] In an embodiment according to aspects of the invention, the measurement results can be secured with a two-channel measurement. This can be done, for example, by carrying out an additional differential measurement between the respective balancing chambers before and after the dialyzer 3 by weighing the chambers (e.g. chamber 4 with chamber 6 and chamber 5 with chamber 7), in particular with the aid of a rocker device not shown in the Figures, on which the corresponding chambers are mounted. Alternatively, the total weight of two chambers, e.g. of the chambers 4 and 6 and the chambers 5 and 7, can be determined on a scale likewise not shown in the Figures, and the results of the individual scales can be compared by forming a difference.

[0083] FIGS. 2 and 3 can be used to illustrate a second embodiment variant of the invention. The second embodiment differs from the first embodiment shown in FIG. 2 in that the components in FIG. 2 within the dashed borders are replaced by the components shown in FIG. 3. In particular the balancing chambers 4, 5, 6, 7 are identical in both embodiments. In the following description of the second embodiment, only the fresh flow side of the device 1 is described and it is pointed out that the used flow side of the device is designed accordingly and modified compared to the first embodiment of FIG. 2.

[0084] In this embodiment of the device 1, the balancing chambers 4 and 5 or 6 and 7 are not parallel to each other but arranged in series. The balancing chambers 5 and 6 have approximately double or more than double the volume of the chambers 4 and 7 arranged in series with them. On the fresh flow side, the fresh flow pump 17 continuously pumps treatment fluid from the second balancing chamber 5 through the dialyzer 3. The measuring device 32 or alternatively a flow sensor can be used to determine the (mass) flow caused by this pump 17. The first balancing chamber 4 on the fresh flow side is used for the actual balancing. The weight of the treatment fluid present in it is continuously measured by the measuring device 32 located below the chamber 4. The first balancing chamber 4 on the fresh flow side has, similar to the first embodiment of FIG. 2, two switching points, namely empty (e.g. 20 g) and full (e.g. 80 g). If the balancing chamber 4 is empty (i.e. contains only 20 g liquid), the valve 45 opens while the valve 34 closes, so that the first fresh flow pump 9 fills the first balancing chamber 4 on the fresh flow side. Since the ventilation opening 31 of balancing chamber 4 is then closed, any air in the chamber 4 is compressed and the pressure in the chamber 4 increases. As soon as the first balancing chamber 4 on the fresh flow side is full (i.e. contains 80 g treatment fluid), the valve 45 closes and the valve 34 opens. The pressure built up in the first balancing chamber 4 on the fresh flow side (or due to a height difference which may exist between chambers 4 and 5) causes treatment fluid to flow from the first balancing chamber 4 on the fresh flow side into the second balancing chamber 5 on the fresh flow side. As soon as the first chamber 4 is empty (i.e. contains only 20 g treatment fluid), the valve 34 closes and the valve 45 opens and the cycle starts again. If it is ensured that treatment fluid flows from the first balancing chamber 4 on the fresh flow side into the second balancing chamber 5 on the fresh flow side to a sufficient extent or at a sufficient frequency, it is never completely drained. Thus, the pump 17 can provide a continuous flow through the dialyzer 3. It should be noted that only the measuring device 32 under the first balancing chamber 4, 6 is sufficient for balancing.

[0085] The device 1 according to the second embodiment is also suitable for degassing and set up for creating a negative pressure in the treatment fluid by a constriction 33 in the internal fluidic system 2, here in front of the fresh flow pump 9. Any air bubbles generated thereby will accumulate in the first balancing chamber 4 on the fresh flow side, resulting in an increase in pressure. This increases the outflow speed of the treatment fluid from the balancing chamber 4 into the balancing chamber 5. To avoid excessive pressures in the chamber 4, it is equipped with a pressure relief valve arranged in the ventilation opening 31 and not shown in FIG. 3.

[0086] Compared to the first embodiment (FIG. 2), the second embodiment of the invention has the advantage that fewer valves are required. However, the chamber volume of the chambers 5 and 7 is larger than that of the first embodiment and the third embodiment described below.

[0087] FIGS. 2 and 4 can be used to illustrate a third embodiment variant of the invention. The third embodiment differs from the first embodiment shown in FIG. 2 in that the components in FIG. 2 within the dashed borders are replaced by the components shown in FIG. 4. In the following description of the third embodiment, only the fresh flow side of the device 1 is described and it is pointed out that the used flow side of the device is designed accordingly and modified compared to the first embodiment of FIG. 2.

[0088] Compared to the first embodiment, their pumps 9, 17, 19 and 27 are replaced by correspondingly arranged linear motors 35, 36, 37, 38. The linear motors 35, 36, 37, 38 interact with pistons 39, 40, 41, 42 movably arranged in the corresponding balancing chambers 4, 5, 6, 7. The pistons 39, 40, 41, 42 are guided in the respective chamber 4, 5, 6, 7 and sealed against the chamber wall, so that the chambers 4, 5, 6, 7 each form a cylinder belonging to the respective piston 39, 40, 41, 42. The chambers 4, 5, 6, 7 are filled and emptied with a movement of the pistons 39, 40, 41, 42 therein caused by the linear motors 35, 36, 37, 38. The pistons can be arranged either hanging or standing within the scope of the invention. The individual balancing chambers 4, 5, 6, 7 may be thermally insulated. Within the scope of the invention, their size is between approx. 20 ml to approx. 1500 ml. Depending on the size of the chambers 4, 5, 6, 7, the switching cycle of the pistons 39, 40, 41, 42 changes.

[0089] The third embodiment shown in FIG. 4 has the advantage over the first embodiment shown in FIG. 2 that the mass of the treatment fluid in the respective chamber 4, 5, 6, 7 can be better adjusted. If the target weight is exceeded, i.e. there is too much treatment fluid in the respective chamber 4, 5, 6, 7, the linear motor 35, 36, 37, 38 can pump back part of the treatment fluid. A disadvantage compared to the first embodiment is that venting of chambers 4, 5, 6, 7 is not possible, each linear motor 35, 36, 37, 38 and the associated piston 39, 40, 41, 42 are additionally weighed during balancing by the measuring device 32 and the gravity pressure (hydrostatic pressure) is not decoupled and is therefore also measured by measuring device 2.

[0090] A fourth embodiment of device 1 according to aspects of the invention is shown in FIG. 5. On the fresh flow side (upstream of dialyzer 3), there is only one (single) balancing chamber 43 on the fresh flow side, and on the used flow side (downstream of the dialyzer 3) there is only one (single) used flow side balancing chamber 44. The first fresh flow pump 9 fills the balancing chamber 43 on the fresh flow side very quickly (e.g. with 10 times the dialysate flow). When the filling process is completed, the second fresh flow pump 17 delivers treatment fluid from balancing chamber 43 at a constant rate until the chamber 43 is empty. In the same way, the first used flow pump 19 fills the balancing chamber 44 on the used flow side with a constant flow rate. When the balancing chamber 44 is full, the second used flow pump 27 empties the chamber 44 with a high flow rate (e.g. 10 times the flow rate). In this way, a quasi-continuous dialysate flow is generated particularly easily. The cycle repeats itself periodically. Measurement and balancing are carried out in the same way as for the embodiments described above.

[0091] FIGS. 6 and 7 show possible configurations of the first and second embodiments of the invention. These are four separate chambers 4, 5, 6, 7, under each of which a measuring device 32 is installed. The valves 12, 13, 14, 15 and 22, 23, 24, 25 are mounted separately from the chambers 4, 5, 6, 7 in both exemplary embodiments in order to decouple the chambers 4, 5, 6, 7 as far as possible in mechanical terms. For example, switching process of the valves are not transferred directly to the measuring devices 32, here in the form of force sensors 32.

[0092] All chambers 4, 5, 6, 7 are illustrated with open top, but they are provided with a cover (not shown in FIGS. 6 and 7) having an overflow connection and/or a hydrophobic filter, for example.

[0093] Finally, FIG. 8 shows a possible implementation of the third embodiment. This is based on the implementation shown in FIG. 6. The chambers 4, 5, 6, 7 were supplemented by the linear motors 35, 36, 37, 38. These move each one of the pistons 39, 40, 41, 42 up and down in the respective chamber 4, 5, 6, 7, providing the desired flow of treatment fluid.