A portable oxygen concentrator includes a reservoir adapted to store oxygen-enriched gas, a delivery valve adapted to communicate with the reservoir, a pressure sensor adapted to measure a reservoir pressure within the reservoir and to measure a pressure drop across the delivery valve, and an input device adapted to receive a pulse does setting. A controller coupled to the pressure sensor and monitors the reservoir pressure and the pressure drop across the delivery valve. The controller is also coupled to the delivery valve to selectively open the delivery valve for pulse durations based on the pulse dose setting to deliver pulses of gas from the reservoir to a user. The controller further adjusts the pulse durations based at least partially upon the reservoir pressure and the pressure drop across the delivery valve.