A CPAP system comprising: a flow generator including a low inertia blower that supplies pressurized breathable gas; a patient interface ; an air delivery conduit interconnecting the flow generator and the patient interface , the air delivery conduit including a conduit portion having an internal diameter less than 19 mm; and a controller adapted to control the pressure delivered to the patient interface based on the speed of the blower and a pressure compensation calculation, wherein the pressure compensation is based on the equation: P1 − P2 = K 1 Q 2 + K 2 Q , where K 1 is a constant related to the length and diameter of the air delivery conduit , K 2 is a constant based on a flow versus pressure drop plot, and Q is flow rate determined with a flow sensor adapted to measure and detect changes in flow, P1 is the pressure generated from the blower, P2 is the pressure delivered to the patient, characterized in that the pressure output of the blower is adjusted by a feedforward output calculated by multiplying the change in flow by a coefficient K f , wherein flow feedforward control includes a sensor adapted to measure and detect changes in flow, when changes in flow are detected the controller adjusts the pressure output from the blower to reduce the level of pressure disturbance delivered to the patient interface, wherein K f is based on a previous characterization of the system to determine the level of pressure disturbance that will occur for each of the components of the system at different levels of flow, and wherein the final pressure adjustment is a sum of said feedforward output and a feedback output for said pressure output. a flow generator including a low inertia blower that supplies pressurized breathable gas; a patient interface ; an air delivery conduit interconnecting the flow generator and the patient interface , the air delivery conduit including a conduit portion having an internal diameter less than 19 mm; and a controller adapted to control the pressure delivered to the patient interface based on the speed of the blower and a pressure compensation calculation, wherein the pressure compensation is based on the equation: P1 − P2 = K 1 Q 2 + K 2 Q , where K 1 is a constant related to the length and diameter of the air delivery conduit , K 2 is a constant based on a flow versus pressure drop plot, and Q is flow rate determined with a flow sensor adapted to measure and detect changes in flow, P1 is the pressure generated from the blower, P2 is the pressure delivered to the patient, characterized in that the pressure output of the blower is adjusted by a feedforward output calculated by multiplying the change in flow by a coefficient K f , wherein flow feedforward control includes a sensor adapted to measure and detect changes in flow, when changes in flow are detected the controller adjusts the pressure output from the blower to reduce the level of pressure disturbance delivered to the patient interface, wherein K f is based on a previous characterization of the system to determine the level of pressure disturbance that will occur for each of the components of the system at different levels of flow, and wherein the final pressure adjustment is a sum of said feedforward output and a feedback output for said pressure output. <EOS>