Automated control mechanisms and methods for controlling fluid flow in a hemodialysis apparatus

A method for controlling fluid flow in a hemodialysis apparatus where a reciprocating diaphragm blood pump moves blood through a dialyzer and a dialysate pump moves dialysate through the dialyzer, the method comprising:

• receiving, by a controller, fluid pressure information from a pressure sensor in fluid communication with a control chamber of a blood pump comprising a reciprocating diaphragm between a blood chamber and the control chamber;
• causing, by the controller, a pneumatic valve to open and close to thereby apply time-varying pressure on the diaphragm of the blood pump during a fill stroke of the blood pump, the pneumatic valve fluidly connecting the control chamber with a pressure source;
• monitoring, by the controller, a pressure variation in the control chamber measured by the pressure sensor;
• determining, by the controller, a blood flow metric based on the pressure variation measured during the fill stroke;
• alerting, by the controller, a user that blood flow is inadequate via a graphical user interface when the blood flow metric drops below a predetermined value;
• and
• completing one or more blood pump fill strokes after alerting the user that blood flow is inadequate and before stopping the dialysate pump in response to the blood flow metric.