Dialysate flow control
Method and apparatus for controlling the dialysate flow in a dialysis device. A change of the value of a control factor, caused by a variation of a property of the dialysate or of the blood or by a change of the dialysate flow, is determined in order to control the dialysate flow. The control factor is a measure for the exchange of substances via the dialyzer and thus the effectiveness of the dialyzer. If the change of the value of the control factor exceeds a limit, the dialysate flow is increased. On the other hand, the dialysate flow is reduced if the change of the value of the control factor falls short of the limit range.
1. A method for controlling a dialysate flow, the method comprising the steps of:
perfusing a blood chamber of a dialyzer with blood and a dialysis chamber, which is separated from the blood chamber by a semi-permeable membrane, with a dialysate,
controlling the dialysate flow through the dialysis chamber of the dialyzer when the value of a control factor is changed and does not lie within a limit range, caused by a continuous modulation of a property of the dialysate, whereby the control factor is a measure for the exchange of substances via the dialyzer and the controlling includes:
continuously modulating the value of the property of the dialysate,
determining the change of the value of the control factor caused by continuously modulating the property of the dialysate during treatment, and
increasing the dialysate flow if the change of the value of the control factor exceeds the limit range, or reducing the dialysate flow if the change of the value of the control factor falls below the limit range.
2. The method according to claim 1 , wherein for determining the change of the value of the control factor, the property of the dialysate is continuously modulated for at least a time interval.
3. The method according to claim 1 , wherein the property of the dialysate is the electrolyte concentration or the temperature.
4. A device for controlling a dialysate flow, comprising
a dialyzer with a blood chamber for perfusing with blood and a dialysis chamber separated from the blood chamber by a semi-permeable membrane for perfusing with a dialysate,
a generator for perfusing the dialysate flow through the dialysis chamber,
a determining unit configured for determining a change in the value of a control factor that is a measure for the exchange of substances over the dialyzer, based on a modulation in the values of a property of the dialysate determined before and after the dialyzer, respectively, and
a control facility configured to control the dialysate flow through the dialysis chamber of the dialyzer, if a property of the dialysate is modulated during treatment and if a change of the value of the control factor continuously at any time point during treatment caused by the modulation of a property of the dialysate does not lie within a limit range,
the control facility instructs the generator to increase the dialysate flow if the change of the value of the control factor exceeds the limit range, and to reduce the dialysate flow, if the change of the value of the control factor falls below the limit range.
5. The device according to claim 4 , wherein the device further has means for continuously modulating the property of the dialysate.
6. The device according to claim 4 , wherein the property of the dialysate is the electrolyte concentration or the temperature.
7. A device for the extra-corporeal blood treatment comprising a device according to claim 4 .
8. The method according to claim 1 , further comprising adding a substitute to the blood before the perfusing step.