Device for regulating at least one filtration value, haemodialysis machine and corresponding method and use

Abstract

The present invention relates to an apparatus for the regulation of at least one filtration value in a machine for the treatment of a medical fluid, in particular in a blood treatment machine, having at least one centrifugal pumping means, to a hemodialysis machine and to a method and to a use therefor.

Claims

1. A method for the regulation of at least one blood filtration value in a machine cooperating with a disposable cassette for the treatment of blood in an extracorporeal blood circuit having at least one centrifugal blood pump, characterized in that the centrifugal blood pump has a driving part located in the machine and a driven part located in the disposable cassette and coupled with the driving part in a contactless manner, wherein the machine comprises a control device for regulating speed of the centrifugal blood pump, and characterized in that the viscosity of the blood is determined indirectly and/or directly by speed and driving torque of the centrifugal blood pump downstream of a blood filter, hematocrit of the blood is determined based solely on the viscosity determined, and with the at least one blood filtration value being regulated directly or indirectly by the control device with reference solely to the hematocrit determined based on viscosity.

2. A method in accordance with claim 1, characterized in that the centrifugal blood pump is operated in at least one conveying mode and/or at least one measurement mode.

3. A method for regulating filtration of blood in a machine cooperating with a disposable cassette in an extracorporeal blood circuit comprising the steps of determining viscosity of the blood indirectly or directly based on speed and driving torque of a centrifugal blood pump downstream of a blood filter, the centrifugal blood pump having a driving part located in the machine and a driven part located in the disposable cassette and coupled with the driving part in a contactless manner, wherein the machine comprises a control device for regulating speed of the centrifugal blood pump, determining hematocrit of the blood based solely on the determined viscosity, and regulating directly or indirectly by the control device at least one blood filtration value based solely on the determined hematocrit based on viscosity.

4. The method of claim 3, wherein the centrifugal blood pump is operated in at least one of a conveying mode, a measurement mode, multiple conveying modes, and multiple measurement modes.

5. The method of claim 3, wherein the driving part transmits torque by a magnetic coupling to the driven part.

6. The method of claim 3, wherein the machine for the treatment of blood is a hemodialysis machine, and wherein the at least one filtration value is at least one of ultrafiltration rate and ultrafiltration goal.

7. The method of claim 3, wherein the blood filtration value is blood volume flow.

8. The method of claim 3, wherein the centrifugal blood pump has an inlet and an outlet, at least one of the inlet and the outlet capable of closing.

9. The method of claim 8, wherein the centrifugal blood pump operates in a measurement mode when at least one of the inlet and outlet is closed.

10. The method of claim 8, wherein the filtration value is volume flow of the blood determined by at least one flow measurement sensor arranged downstream or upstream of the centrifugal blood pump.

11. The method of claim 8, wherein the viscosity is determined by circulating the blood in the centrifugal blood pump at a speed of 200 r.p.m. or less.

12. The method of claim 3, wherein the machine is a hemodialysis machine.

13. The method of claim 12, wherein the hemodialysis machine has a mount holding the disposable cassette.

Description

(1) Further details and advantages of the invention will now be explained in more detail with reference to an embodiment shown in the drawing.

(2) There is shown:

(3) FIG. 1: the correlation between the viscosity and the hydraulic torque at a rotor speed of a centrifugal pump of 4000 r.p.m.

(4) An embodiment of the invention by means of which a realization of the invention can take place particularly advantageously is provided in that a centrifugal pump is used instead of an occluding peristaltic hose pump for blood transport in the extracorporeal blood circuit in a hemodialysis machine. This centrifugal pump is in this respect used on the one hand in a conveying mode for the conveying of blood and on the other hand in a measurement mode for the determination of the viscosity of the blood. This value for the viscosity of the blood determined by the measurement is further used to determine the hematocrit content of the blood. In this respect, the relative blood volume can be determined with reference to the time course of the hematocrit. A control variable for the ultrafiltration is hereby generated. The apparatus in accordance with the invention is an integral element of the hemodialysis machine in this embodiment.

(5) The ultrafiltration rate preset by the physician and the ultrafiltration target, that is, the total quantity of removed water is regulated in accordance with the invention such that no longer the absolute quantity of the fluid which is removed from the blood is monitored, but the concentration of the water in the blood via its viscosity or hematocrit content and its time course. The centrifugal pump is switched over regularly, that is, at periodically repeating intervals, from the blood conveying mode into a measurement mode for the determination of the viscosity.

(6) The determination of the viscosity can also be determined during the conveying operation with a know fluid flow. An interruption of the fluid conveying is then no longer necessary.

(7) For operation in the measurement mode, the pump inlets and outlets are closed for this purpose, for which purpose corresponding closure means are provided. They can, for example, be clamps or plungers which connect the inflow and outflow lines by compression. The blood in the pump chamber is then recirculated. The viscosity of the recirculating fluid determines the speed of the rotor of the centrifugal pump at a specific driving torque of the pump. The rotor speed can in this respect be measured by known measurement devices (e.g. Hall probe, speedometer cable). The rotor speed is approximately directly proportional to the operating voltage of the centrifugal pump, so that the operating voltage can also be used as a measure for the rotor speed. The driving torque is approximately directly proportional to the operating current of the centrifugal pump so that the operating current can also be used as a measure for the driving torque. With a known rotor speed and a known driving torque of the centrifugal pump, it is possible to draw a conclusion on the viscosity of the recirculating fluid. EP 1 284 369 A1 or EP 1 284 370 A1 discloses a method for this purpose to which reference is made in full. Since the viscosity changes or is supposed to change during the operation of the machine for the treatment of a medical fluid, as is in particular the case in a blood treatment machine and here in particular in a hemodialysis machine, the viscosity determined thus represents information on the fluid status of the blood. If the then current viscosity has been determined, a more accuratecorrectedcalculation of the pump volume flow can be carried out using a new offset value of the viscosity. A particularly advantageous regulation of the at least one filtration value, e.g. for the ultrafiltration rate preset by the physician, and of the preset ultrafiltration goal is thereby carried out.

(8) This comparison and the regulation based thereon is preferably carried out by the control and/or regulation means of the hemodialysis machine. For this purpose, separate control and/or regulation means can be provided in the hemodialysis machine; it is, however, equally possible that the control and/or regulation takes place by the central control and regulation unit of the hemodialysis machine.

(9) Redundant control and/or regulation means are advantageously provided in this respect.

(10) Additional sensors for the determination of the viscosity of the blood are not necessary when the determination of the viscosity takes place in a measurement module in which the outlets and/or inlets of the centrifugal pumping means are closed. If the determination of the viscosity takes place during the conveying of the medical fluid, at least one additional flow measurement sensor is necessary for the determination of the fluid flow.

(11) Provision is made in a particularly advantageous embodiment that the centrifugal pump has a driving first part and a driven second part which are connected to one another in a magnetically contactless manner. The force transmission or torque transmission from the driving first part to the driven second part of the centrifugal pump thus takes place by means of a magnetic coupling. It is particularly advantageous in this connection when the driven second part of the centrifugal pumping means, that is, for example, the pump rotor of the centrifugal pump as well as the corresponding pump chamber with inflow and outflow, is an element of a disposable made in a cassette-like manner.

(12) Such a cassette-like disposable, which can be made analog to a cassette in accordance with DE 102 24 750 A1, can be inserted into a corresponding mount of the hemodialysis machine, wherein a simple and definite insertion can be preset by corresponding connectors. In this respect, in particular the driving first part of the centrifugal pump can be arranged in the hemodialysis machine itself, and indeed in the region of the mount for the cassette. It is furthermore possible that the closure means for the inflow and the outflow of the centrifugal pump or to the centrifugal pump chamber are formed by plungers which are arranged at the machine side. These plungers can, for example, compress inflows and outflows made in channel-like form to the centrifugal pump chamber.

(13) The details of the determination of the parameters for the regulation of the ultrafiltration will be presented theoretically in the following:

(14) The initially introduced Table 1 shows that the viscosity changes much more noticeably at different hematocrit values than the density. In accordance with the invention, the regulation of the ultrafiltration value or the parameter for the ultrafiltration takes place with reference to the measurement of the viscosity of the blood. This measurement takes place directly in the blood and is not dependent on the quality of the disposable. A magnetically journalled disposable centrifugal pump is used for the measurement. The pump conveys the blood through the dialyzer. Occasional closing of the pump inlets and outlets results in a 100% recirculation via the rotor vane. The viscosity of the recirculating fluid determines the speed of the rotor of the centrifugal pump at a specific driving torque of the pump. The rotor speed can in this respect be measured by known measurement devices (e.g. Hall probe, speedometer cable). The rotor speed is approximately directly proportional to the operating voltage of the centrifugal pump, so that the operating voltage can also be used as a measure for the rotor speed. The driving torque is approximately directly proportional to the operating current of the centrifugal pump so that the operating current can also be used as a measure for the driving torque. With a known rotor speed and a known driving torque of the centrifugal pump, it is possible to draw a conclusion on the viscosity of the recirculating fluid. EP 1 284 369 A1 or EP 1 284 370 A1 discloses a method for this purpose to which reference is made in full. Since the viscosity changes or is supposed to change during the operation of the machine for the treatment of a medical fluid, as is in particular the case in a blood treatment machine and here in particular in a hemodialysis machine, the viscosity determined thus represents information on the fluid status of the medical fluid and in particular of the blood.

(15) If the then current viscosity has been determined, a more accuratecorrectedcalculation of the pump volume flow can be carried out using a new offset value of the viscosity.

(16) The interconnections for the determination of the viscosity of the blood are shown again in the following:

(17) Brookshier and Tarbell describe in Biorheology (Volume 28: p. 569-587, Pergamon Press plc., USA 1992) the dependence of the viscosity of the blood on the hematocrit: =1,4175+5,878. Hkt15,98.Math.Hkt.sup.2+31,964.Math.Hkt.sup.3, where HCT in %/100 and in cP.

(18) The hydraulic torque M.sub.L and thus also the hydraulic power of centrifugal pump P.sub.L=M.sub.L are parameters which depend on the density and on the viscosity v of the fluid within the pump.

(19) In this respect there is furthermore a linear connection between the density and the volume flow. The same applies to the portion of the hydraulic torque which is independent of the volume flow and which likewise has a linear dependence on the density. There is furthermore a non-linear dependence of the portion of the hydraulic torque independent of the volume flow on the viscosity. Since the centrifugal pump is magnetically journalled and no mechanical friction losses at all hereby occur, this is mainly due to the hydraulic friction losses between the blade wheel and the housing.

(20) On a blockage of the throughflow through the pump with any desired speed, the following relationship results for the hydraulic torque:
M.sub.L(Q=0)=.Math.(k.sub.2(v).Math..sup.2+k.sub.1(v).Math.).

(21) In this respect, the pump parameters k have a squared dependence on the viscosity. The pump works comparably to a rotary viscometer under these aforesaid marginal conditions.

(22) If a fixed speed is used, it is possible considerably to reduce the calculation effort. The viscosity can then be calculated as follows:
=k.sub.2M.sub.L0.sup.2+k.sub.1M.sub.L0+k.sub.0.

(23) This relationship is shown at a rotor speed of 4000 r.p.m. in the FIGURE.

(24) The torque can be determined via the current pick-up of the centrifugal pump. If this parameter is known, the viscosity can be obtained and the hematocrit can be determined from it. With the hematocrit, the relative blood volume is in turn calculated and one thus has the return parameter for the regulation of the ultrafiltration.

(25) It must also be pointed out at this point that the brief closing of both pump sides does not result in any damage to the blood.