The apparatus centers on a driver (30) used in conjunction with a gas delivery. The driver (30) includes a valve (34), adapted to receive gas from a source, for regulating the flow of gas to the delivery device (10) in response to a control signal. A controller (36), connected to the valve (34), generates the control signal so that the valve (34) periodically modifies the flow of gas, thereby injecting a sigh cycle. A sensor (46) is connected to sense the airway pressure and generate a pressure signal representative of the airway pressure. The controller (36) periodically modifies the flow of gas in response to this pressure signal. It is especially preferred to initiate a sigh cycle when a drop in airway pressure is sensed.