Apparatus for extracorporeal blood treatment and a control method therefor

A method for reducing the risk of infusion of gas microbubbles in a patient, the method comprising:

• moving a first actuator to generate a variable flow comprising a constant flow component of a desired flow value and a variable flow component oscillating about the constant flow component, the variable flow component having a substantially nil average value, the variable flow component generating in an expansion chamber a pressure progression that is variable in time, the pressure progression comprising a pressure component oscillating about a mean value;
• receiving from at least one sensor associated with the expansion chamber and configured to sense pressure values internally of the expansion chamber, a plurality of pressure values for a time period comprising a plurality of pressure oscillations about the mean value, the pressure values being measured at successive time instants;
• calculating, as a function of the pressure values, a control value that is representative of the oscillating pressure component;
• comparing the control value representing the oscillating pressure component with a reference threshold;
• and
• determining, following the comparison, the occurrence or not of a condition of variation of a level in the expansion chamber.