Apparatus for extracorporeal blood treatment and a control method therefor

An apparatus for extracorporeal blood treatment comprising:

• at least a treatment unit having at least a first chamber and at least a second chamber separated from one another by a semipermeable membrane;
• at least a blood removal line connected to an inlet port of a first chamber and predisposed to remove blood from a patient;
• at least a blood return line connected to an outlet port from the first chamber and predisposed to return treated blood to the patient;
• at least an expansion chamber placed at least in one of the blood removal line and the blood return line, the expansion chamber being arranged in use to contain a predetermined quantity of gas in an upper portion and a predetermined quantity of blood at a predetermined level in a lower portion, the blood removal line, the blood return line, the first chamber and the at least an expansion chamber being part of an extracorporeal blood circuit;
• at least a blood pump operating at the extracorporeal blood circuit such as to move the blood in the circuit;
• at least a pressure sensor associated to the expansion chamber and configured such as to enable determining pressure values internally of the expansion chamber;
• at least a fluid evacuation line connected to an outlet port of the second chamber;
• a control unit connected to the at least a pressure sensor, with the pump, and configured to:
• move the blood pump such as to generate a variable blood flow comprising a constant flow component of a desired blood flow value and a variable flow component having a substantially nil mean value, the variable blood flow generating at least in the expansion chamber a pressure progression that is variable in time comprising a pressure component oscillating about a mean value;
• receive from the at least a sensor a plurality of pressure values for a time period comprising a plurality of pressure oscillations about the means value, the pressure values being measured at successive time instants;
• calculate, as a function of the pressure values, a control value that is representative of the oscillating pressure component,
• compare the control value representing the oscillating pressure component with a reference threshold, and
• determine, following the comparison, the occurrence or not of a condition of variation of the blood level in the expansion chamber.