Determining the state of clogging of a filter equipping a medical ventilator

The invention relates to a method for determining the level of clogging of a filter (16) arranged in a breathing assistance apparatus comprising a turbine (5) fluidly connected to the electric motor, upstream side to a feed conduit air (4) including an air inlet fluidly communicating with the ambient atmosphere and, downstream side, to a gas supply line (8), a pressure sensor (15) arranged to measure a gas pressure in the air supply conduit (4), a flow sensor (6) arranged to measure a gas flow rate in the gas supply line (8), driving means (9) cooperating with the turbine (5), the pressure sensor (15) and the flow sensor (6) and a filter (16) arranged on the path of the gas. The control means (9) controls the turbine (5) for supplying a given gas flow rate (Q), the pressure sensor (15) measures the pressure exerted in the air supply conduit (4) for grant of a given gas flow rate (Q), and transmit a pressure signal to the control means (9), and the control means (9) processes the pressure signal transmitted to obtain a pressure drop value (APRR) corresponding to a level of fouling of the filter and determine a fouling ratio (RE) of the filter (16) from the pressure drop value (APRR) and a standard pressure value (APRE) prefixed.