Patent ID: 8353291

Claim:
A breathing assistance system configured to determine pressure drop, comprising: a gas delivery system configured to deliver gas toward a patient; one or more sensors configured to measure one or more parameters of gas delivered by the gas delivery system; a calibration module configured to: perform one or more positive-pressure pressure drop calibration tests, each positive-pressure pressure drop calibration test measuring a pressure drop in gas flowing through a breathing assistance system apparatus at a particular positive flow rate; and perform one or more negative-pressure pressure drop calibration tests, each negative-pressure pressure drop calibration test measuring a pressure drop in gas flowing through a breathing assistance system apparatus at a particular negative flow rate; and based at least on the results of the one or more pressure drop calibration tests, generate: (a) a positive-pressure non-linear equation relating (a) pressure drop in gas flowing through the breathing assistance system apparatus with (b) flow rate of gas flowing through the breathing assistance system apparatus, for positive-pressure gas flow; and (b) a negative-pressure non-linear equation relating (a) pressure drop in gas flowing through the breathing assistance system apparatus with (b) flow rate of gas flowing through the breathing assistance system apparatus, for negative-pressure gas flow; wherein the negative-pressure non-linear equation is different than the positive-pressure non-linear equation; and a pressure drop calculation module configured to determine pressure drops in gas flowing through the breathing assistance system apparatus for various flow rates based at least on the non-linear equation.