NASAL 2-LEVEL POSITIVE-PRESSURE VENTILATION IN NORMAL SUBJECTS - EFFECTS ON THE GLOTTIS AND VENTILATION

The purpose of this study was to examine the behavior of the glottis d uring intermittent positive-pressure ventiliation (nIPPV) using a two- level positive-pressure ventilator and to compare the glottic adaptati on to this ventilatory mode with the one observed using volumetric ven tilators, recently reported by us. Six healthy subjects were studied d uring both wakefulness and sleep. Their glottis was continuously monit ored through a fiberoptic bronchoscope. We measured breath by breath t he widest inspiratory angle formed by the vocal cords at the anterior commissure, the corresponding tidal volume, and other indices. We used the controlled ventilatory mode. The expiratory pressure was kept at 4 cm H2O, and the inspiratory pressure was increased by steps from 10 to 15 to 20 cm H2O. Increases in inspiratory pressure did not always l ead to increases in effective ventilation reaching the lungs. This was due to a significant narrowing of the glottis by adduction of the voc al cords in all subjects. Periodic breathing with or without apneas we re common during wakefulness, but especially during sleep, representin g 10.5 +/- 11% (SD) of total sleep time. We conclude that effective ve ntilation during nIPPV using a two-level positive-pressure ventilator in the controlled mode is less predictable and less stable than during nIPPV using volumetric ventilators.