Original recordings of several breathing waveforms from the experimental CPAP ventilator without PI controller. a) Flow rate. b) Low pressure. c) Airway pressure. The pressure setting is at 8 cmH2O. The maximum inspiratory flow rate is about 50 L/min and the maximum expiratory flow rate about -10 L/min. The output port pressure fluctuation caused by patient's breath is within the range of ± 1 cmH2O.