GLOTTIC APERTURE AND EFFECTIVE MINUTE VENTILATION DURING NASAL 2-LEVEL POSITIVE PRESSURE VENTILATION IN SPONTANEOUS MODE

Our goal was to verify glottic behavior and its effects on effective m inute ventilation during intermittent positive pressure ventilation ap plied at increasing inspiratory pressure levels through a nasal mask ( nIPPV) using a two-level positive pressure ventilator (two-level IPPV) in spontaneous mode. Ten subjects were studied while awake. The spont aneous mode was used at three levels of inspiratory positive airway pr essure (IPAP): 10, 15, and 20 cm H2O. The expiratory pressure was kept at 4 cm H2O. Records of spontaneous breathing without nIPPV were also performed. The glottis was continuously monitored through a fiberopti c bronchoscope. We measured, breath by breath, the widest inspiratory angle formed by the vocal cords at the anterior commissure, the corres ponding tidal volume (with respiratory inductive plethysmography), the respiratory frequency and other indices. Our data during wakefulness show that inspiratory pressures of 10 and 15 cm H2O did not result in increases in effective minute ventilation with respect to spontaneous breathing. Only at 20 cm H2O of IPAP did effective minute ventilation increase. This was due essentially to a decrease in respiratory freque ncy with increasing pressures, offsetting increases in tidal volume at 10 and 15, but not at 20 cm H2O of inspiratory pressure. Changes in e nd-tidal CO2 suggest that alveolar ventilation increased due to the ch ange in breathing pattern. Contrary to what we observed previously wit h either two-level IPPV used in the controlled mode, or nIPPV performe d with volumetric ventilators, the glottis did not play any noticeable role in the control of effective minute ventilation.