A ventilating system for providing inspiratory air to and receiving expiratory air from a patient in a respiratory cycle. A ventilator has an inspiratory outlet for providing inspiratory air and an expiratory inlet for receiving expiratory air. A patient circuit in fluid communication with the lungs of the patient conveys inspiratory air during the inspiratory phase and expiratory air during the expiratory phase. A flow transducer in fluid communication with the patient circuit detects a minimum volume of expiratory air in the patient circuit during the expiratory phase. An elastic reservoir in fluid communication with the patient circuit and the flow transducer expands to a first volume during the inspiratory contracts to a second volume during the expiratory phase. The volume difference between the first volume and the second volume is at least equal to the minimum volume threshold.