Methods for providing expiratory pressure relief in positive airway pressure therapy

In a CPAP apparatus having an electric motor, an impeller rotated by the motor, a patient interface, an air delivery conduit for delivering air from the impeller to the patient interface, a sensor for determining the pressure in the patient interface, and a control mechanism that causes air to be delivered at a desired pressure to the patient interface, and that detects transitions between inhalation and exhalation of a respiratory cycle of a patient;

• a method of controlling the motor operation comprising the steps of:
• controlling the interface pressure to drop at the start of expiration by an expiratory relief pressure (ERP), and
• then controlling the pressure to rise to an inspiratory level at or shortly before the end of expiration, or at the onset of an expiratory pause, if any,
• wherein the expiratory pressure follows a template that is a function of the expected expiration time.

A method of determining the expiratory proportion of a breath, p, comprising the steps of:

• monitoring a respiratory flow of air of a patient;
• calculating an expected duration of expiration, d, from at least one prior breath from said respiratory flow;
• determining the start of exhalation of the patient within the breath;
• calculating a time, t, since the start of exhalation of the patient;
• and
• calculating p from the ratio of t and d.

A method of determining the expiratory pause fraction of a breath, k, comprising the steps of:

• continuously calculating a flow signal indicative of a respiratory flow of air to a patient;
• calculating a rate of change of said flow signal;
• determining a fuzzy extent to which the flow signal is indicative of an expiratory pause from said flow and rate;
• calculating a value F from low pass filtering said fuzzy extent;
• and
• calculating the expiratory pause fraction, k, from the equation:
• k=1−F.