Automated control mechanisms in a hemodialysis apparatus
A hemodialysis apparatus comprising diaphragm pumps for the movement of both dialysate and blood, and under the control of a controller, is capable of detecting blood flow conditions that give rise to an alarm and implement procedures to adjust, pause, or halt the pumping of dialysate and/or blood. The controller can direct the application of a time-varying pressure to fluid in the control chamber of a blood pump, and monitor the resulting pressure waveform during a fill stroke of the blood pump. A deviation of the measured pressure variation from an expected value can give rise to an alert to a user and to the initiation of an adjustment, pause, or cessation of the dialysate pump's activity.
1. A system for controlling fluid flow in a hemodialysis apparatus comprising:
a dialysate pump constructed and arranged to receive a fluid from a dialysate outlet of a dialyzer;
a blood pump comprising a reciprocating diaphragm constructed and arranged to deliver blood from an extracorporeal blood circuit to a blood inlet of the dialyzer, a pumping chamber of the blood pump separated from a control chamber of the blood pump by a flexible diaphragm, the control chamber constructed and arranged to contain a control fluid at a positive or a negative pressure to operate the diaphragm;
a pressure sensor constructed and arranged to measure a pressure of the control fluid contained in the control chamber of the blood pump;
a controller adapted and programmed to receive information from the pressure sensor, and programmed to operate a valve connecting a source of the control fluid to the control chamber of the blood pump;
wherein the controller is adapted and programmed to control the valve to generate a time-varying pressure waveform of the control fluid in the control chamber during a fill-stroke of the blood pump and to monitor a resulting pressure variation in the control chamber, and
wherein the controller is adapted and programmed to initiate a procedure to pause or stop the dialysate pump if a magnitude of the measured pressure variation deviates from a pre-determined value, the procedure comprising alerting a user of a fault condition and waiting a pre-determined time period for a user response to correct the fault condition before pausing or stopping the dialysate pump.
2. The system of claim 1 , wherein the controller is adapted and programmed to compare the resulting pressure variation in the control chamber with a target pressure variation, and wherein a deviation between the resulting pressure variation and the target pressure variation that is greater than a pre-determined difference value causes the controller to initiate the procedure to pause or stop the dialysate pump.
3. The system of claim 1 , wherein the controller is adapted and programmed to compare the measured pressure in the control chamber with a target pressure during time periods when an absolute value of the applied pressure is decreasing, and wherein a deviation between the measured pressure and the target pressure that is greater than a pre-determined difference value causes the controller to initiate the procedure to pause or stop the dialysate pump.
4. The system of claim 2 , wherein the comparison by the controller comprises calculating a cross-correlation value between the measured pressure variation and the target pressure variation, and wherein a cross-correlation value that is less than a pre-determined cross-correlation value causes the controller to initiate the procedure to pause or stop the dialysate pump.
5. The system of claim 4 , wherein the calculated cross-correlation value comprises a phase-insensitive cross-correlation value.
6. The system of claim 4 , wherein the controller is adapted and programmed to initiate the procedure to pause or stop the dialysate pump only if the calculated cross-correlation value is less than the pre-determined cross-correlation value for two or more consecutive blood pump fill-strokes.
7. The system of claim 4 , wherein the controller is adapted and programmed to calculate a filtered or averaged cross-correlation value during a fraction of a pump fill-stroke period and re-calculate one or more additional filtered or averaged cross-correlation values during one or more successive fractions of the fill-stroke period, and wherein the controller is further adapted and programmed to compare a highest valued filtered or averaged cross-correlation value during said fill-stroke period with a pre-determined filtered or averaged cross-correlation value to determine whether to initiate the procedure to pause or stop the dialysate pump.
8. The system of claim 1 , wherein the time-varying pressure waveform comprises a sinusoidal pressure waveform.
9. The system of claim 1 , wherein the valve comprises a variable restriction valve.
10. The system of claim 9 , wherein the source of control fluid comprises a source of positively or negatively pressurized gas.
11. The system of claim 1 , wherein the dialysate pump comprises a reciprocating diaphragm, and wherein the pre-determined value is based on a pressure Aduring a normal or full-flow pumping condition.
12. The system of claim 1 , wherein the controller is adapted and programmed to pause or stop the dialysate pump while allowing the blood pump to continue to operate if a flow metric based on the deviation of the magnitude of the measured pressure variation from the pre-determined value exceeds a pre-determined flow metric value.
13. The system of claim 1 , wherein the controller is adapted and programmed to calculate a flow metric comprising a measure of a variation of a peak-to-peak magnitude of the measured pressure.
14. The system of claim 13 , wherein the controller is adapted and programmed to normalize the measured variation of the peak-to-peak magnitude to an expected or pre-determined peak-to-peak pressure variation, or a peak-to-peak pressure variation obtained during a nominal or full flow condition.
15. The system of claim 1 , wherein the controller is adapted and programmed to calculate a flow metric based on a cross-correlation of a desired, expected or nominal pressure and the measured pressure.
16. The system of claim 15 , wherein the flow metric is based on a phase insensitive cross-correlation of the desired, expected or nominal pressure and the measured pressure.
17. The system of claim 15 , wherein the controller is adapted and programmed to set the flow metric to a correlation number derived from the cross-correlation while the diaphragm of the blood pump is moving, and to hold the flow metric at a value reached before the diaphragm reaches an end of its stroke.
18. The system of claim 15 , wherein the controller is adapted and programmed to set the flow metric to a maximum average correlation number during a single pump stroke.
19. The system of claim 15 , wherein the controller is adapted and programmed to display for a user the flow metric during the course of each blood pump fill-stroke.
20. A system for controlling fluid flow in a hemodialysis apparatus comprising:
a dialysate pump constructed and arranged to receive a fluid from a dialysate outlet of a dialyzer;
a blood pump comprising a reciprocating diaphragm constructed and arranged to deliver blood from an extracorporeal blood circuit to a blood inlet of the dialyzer, a pumping chamber of the blood pump separated from a control chamber of the blood pump by a flexible diaphragm, the control chamber constructed and arranged to contain a control fluid at a positive or a negative pressure in contact with the diaphragm;
a pressure sensor constructed and arranged to measure a pressure of the control fluid contained in the control chamber of the blood pump;
a controller adapted and programmed to receive information from the pressure sensor, and programmed to operate a valve connecting a source of the control fluid to the control chamber of the blood pump;
wherein the controller is adapted and programmed to control the valve to generate a time-varying pressure waveform of the control fluid in the control chamber during a fill-stroke of the blood pump and to monitor a resulting pressure variation in the control chamber, and
wherein the controller is adapted and programmed to initiate a procedure able to select from:
adjusting, pausing, and stopping the dialysate pump if a magnitude of the measured pressure variation deviates from a pre-determined value.
21. The system of claim 20 , wherein the controller is adapted and programmed to compare the resulting pressure variation in the control chamber with a target pressure variation, and wherein a deviation between the resulting pressure variation and the target pressure variation that is greater than a pre-determined difference value causes the controller to initiate the procedure able to select from: adjusting, pausing, and stopping the dialysate pump.
22. The system of claim 20 , wherein the controller is adapted and programmed to compare the measured pressure in the control chamber with a target pressure during time periods when an absolute value of the applied pressure is decreasing, and wherein a deviation between the measured pressure and the target pressure that is greater than a pre-determined difference value causes the controller to initiate the procedure able to select from: adjusting, pausing, and stopping the dialysate pump.
23. The system of claim 21 , wherein the comparison by the controller comprises calculating a cross-correlation value between the measured pressure variation and the target pressure variation, and wherein a cross-correlation value that is less than a pre-determined cross-correlation value causes the controller to initiate the procedure able to select from: adjusting, pausing, and stopping the dialysate pump.
24. The system of claim 23 , wherein the calculated cross-correlation value comprises a phase-insensitive cross-correlation value.
25. The system of claim 23 , wherein the controller is adapted and programmed to initiate the procedure able to select from: adjusting, pausing, and stopping the dialysate pump only if the calculated cross-correlation value is less than the pre-determined cross-correlation value for two or more consecutive blood pump fill-strokes.
26. The system of claim 23 , wherein the controller is adapted and programmed to calculate a filtered or averaged cross-correlation value during a fraction of a pump fill-stroke period and re-calculate one or more additional filtered or averaged cross-correlation values during one or more successive fractions of the fill-stroke period, and wherein the controller is further adapted and programmed to compare a highest valued filtered or averaged cross-correlation value during said fill-stroke period with a pre-determined filtered or averaged cross-correlation value to determine whether to initiate the procedure able to select from: adjusting, pausing, and stopping the dialysate pump.
27. The system of claim 20 , wherein the time-varying pressure waveform comprises a sinusoidal pressure waveform.
28. The system of claim 20 , wherein the valve comprises a variable restriction valve.
29. The system of claim 28 , wherein the source of control fluid comprises a source of positively or negatively pressurized gas.
30. The system of claim 20 , wherein the dialysate pump comprises a reciprocating diaphragm, and wherein the pre-determined value is based on a pressure over a period of time generated by the blood pump during a normal or full-flow pumping condition.
31. The system of claim 20 , wherein the controller is adapted and programmed to be able to selectively pause or stop the dialysate pump while allowing the blood pump to continue to operate if a flow metric based on the deviation of the magnitude of the measured pressure variation from the pre-determined value exceeds a pre-determined flow metric value.
32. The system of claim 20 , wherein the controller is adapted and programmed to calculate a flow metric comprising a measure of a variation of a peak-to-peak magnitude of the measured pressure.
33. The system of claim 32 , wherein the controller is adapted and programmed to normalize the measured variation of the peak-to-peak magnitude to an expected or pre-determined peak-to-peak pressure variation, or a peak-to-peak pressure variation obtained during a nominal or full flow condition.
34. The system of claim 20 , wherein the controller is adapted and programmed to calculate a flow metric based on a cross-correlation of a desired, expected or nominal pressure and the measured pressure.
35. The system of claim 34 , wherein the flow metric is based on a phase insensitive cross-correlation of the desired, expected or nominal pressure and the measured pressure.
36. The system of claim 34 , wherein the controller is adapted and programmed to set the flow metric to a correlation number derived from the cross-correlation while the diaphragm of the blood pump is moving, and to hold the flow metric at a value reached before the diaphragm reaches an end of its stroke.
37. The system of claim 34 , wherein the controller is adapted and programmed to set the flow metric to a maximum average correlation number during a single pump stroke.
38. The system of claim 34 , wherein the controller is adapted and programmed to display for a user the flow metric during the course of each blood pump fill-stroke.