EFFECTS OF NASAL POSITIVE-PRESSURE HYPERVENTILATION ON THE GLOTTIS INNORMAL AWAKE SUBJECTS

We have recently observed obstructive apneas during nasal intermittent positive-pressure ventilation (nIPPV) and suggested that they were du e to hypocapnia-induced glottic closure. To confirm this hypothesis, w e studied seven healthy subjects and submitted them to nIPPV while the ir glottis was continuously monitored through a fiber-optic bronchosco pe. During wakefulness, we measured breath by breath the widest inspir atory angle formed by the vocal cords at the anterior commissure along with several other indexes. Mechanical ventilation was progressively increased up to 30 l/min. In the absence of diaphragmatic activity, in creases in delivered minute ventilation resulted in progressive narrow ing of the vocal cords, with an increase in inspiratory resistance and a progressive reduction in the percentage of the delivered tidal volu me effectively reaching the lungs. Adding CO2 to the inspired gas led to partial widening of the glottis in two of three subjects. Moreover, activation of the diaphragmatic muscle was always associated with a s ignificant inspiratory abduction of the vocal cords. Sporadically, com plete adduction of the vocal cords was directly responsible for obstru ctive laryngeal apneas and cyclic changes in the glottic aperture resu lted in waxing and waning of tidal volume. We conclude that in awake h umans passive ventilation with nIPPV results in vocal cord adduction t hat depends partly on hypocapnia, but our results suggest that other f actors may also influence glottic width.