Patent ID: 8413654

Claim:
A method for operating a CPAP apparatus having a flow generator, a patient interface, an air delivery conduit for delivering air from the flow generator to the patient interface, and a control mechanism that causes air to be delivered through the air delivery conduit at desired pressures at the patient interface, the method comprising the steps of: (i) controlling the flow generator to reduce the air flow through the delivery conduit to the patient interface to deliver a lower base level of positive air pressure (“EPAP”) in the patient interface during an expiratory portion of the patient's respiratory cycle; (ii) controlling the flow generator to increase air flow through the delivery conduit to the patient interface during inhalation so as to maintain the pressure in the patient interface at a higher level (“IPAP”) suitable for inhalation, wherein the time for the flow generator to increase the pressure from EPAP to IPAP is a variable rise time; and (iii) monitoring the shape of the inspiratory portion of the respiratory airflow and increasing the rise time upon detection of a shape indicative of the presence of upper airway obstruction, resistance or instability.