We recorded the pressure responses of each of the five auto-CPAP devices. In the first experiment, the normal breathing flow had a rounded inspiratory flow contour with a frequency of eight cycles per minute, an inspiratory time of 1.9 s, and a tidal volume of 500 mL (Fig 2
, top, A). Five degrees of FIFC were simulated, namely, 90% of the maximum inspiratory flow rate (R90), 80% of the maximum inspiratory flow rate (R80), 70% of the maximum inspiratory flow rate (R70), 60% of the maximum inspiratory flow rate (R60), and 50% of the maximum inspiratory flow rate (R50) during the normal (rounded) flow cycle. To produce the FIFC, the normal signal was replaced by a plateau signal when the flow reached the desired percentage of the peak flow on the normal flow contour. Inspiratory time was set to keep the tidal volume at 500 mL. In the second set of experiments, we studied normal (rounded) and FIFC from patients with upper airway resistance syndrome published in the literature.13–14 We used a normal breathing cycle as recorded by Guilleminault et al13(NG) and a flow limitation cycle as recorded by Guilleminault (G1) [Fig 2, bottom, B], as well as a normal breathing cycle as recorded by Clark et al14 (NC), a false flow limitation cycle (FFLC), and two levels of flow limitation (C1 = first flow limitation cycle as recorded by Clark [C1], and second flow limitation cycle as recorded by Clark [C2]). In each set of experiments, each device was tested with CPAP set at 8 cm H2O and 12 cm H2O. The maximum pressure was 12 cm H2O for the 8 cm H2O CPAP level and 16 cm H2O for the 12 cm H2O level.