Effects of nasal intermittent positive pressure hyperventilation on the glottis in normal subjects during sleep. Jounieaux, V., G. Aubert, M. Dury, P. Delguste, and D. O. Rodenstein. Pneumology and EEG Units, Cliniques Universitaires Saint Luc, Universit[acute]e Catholique de Louvain, 1200 Brussels, Belgium
APStracts 2:0084A, 1995.
We have previously observed that, in normal awake subjects passively hyperventilated with intermittent positive pressure ventilation delivered through nasal access (nIPPV), the glottis could interfere with the ventilation. The present study reports on data obtained in the same healthy subjects under nIPPV during stable sleep. In all cases, the glottis was continuously observed through a fiberoptic bronchoscope, actual ventilation was continuously assessed with inductance plethysmography (actual tidal volume : VT, actual minute ventilation estimated breath by breath : VE). End-tidal carbon dioxide concentration (PetCO2) and mask pressure (P) were also continuously recorded. Mechanical ventilation was progressively increased up to 30 l/min. The inspiratory glottic aperture was assessed breath by breath by measuring the widest angle formed by the vocal cords at the anterior commisure during the mechanical insufflation. Glottic measurements were performed only during periods of passive ventilation (absence of respiratory muscle activity assessed through the absence of phasic inspiratory EMGDI activity). In addition, in 4 subjects, CO2 was added to the inspired gas without changing the delivered minute ventilation (CO2 trials). We have observed during stable sleep (stages 2, 3 and 4 NREM sleep together) that increases in delivered minute ventilation (VEd) resulted in progressive narrowing of the glottic aperture, with increases in inspiratory resistance and progressive reductions in the percentage of the delivered tidal volume (VTd) effectively reaching the lungs. For a given level of VEd, comparisons showed that the glottis was significantly narrower during sleep than during wakefulness ($QUOTsleep effect$QUOT). During sleep, there was a significant positive correlation between PetCO2 and glottic width.When considering stage 2 and stage 3-4 NREM sleep separately, the glottis was significantly narrower during stage 2 than during stage 3-4 NREM sleep ($QUOTstage effect$QUOT). Moreover, in 5 out of 9 CO2 trials, glottic aperture increased without changes in sleep stage ($QUOTCO2 effect$QUOT). We also observed a significant negative correlation between glottic width and the delivered minute ventilation, independently of the CO2 level ($QUOTmechanical effect$QUOT). We conclude that during sleep the glottis narrows more than during wakefulness in normal subjects mechanically ventilated with nIPPV. This glottic narrowing results in a decrease in the proportion of the delivered tidal volume effectively reaching the lungs. The mechanisms controlling the glottic width are complex and include sleep, sleep stage, chemical and mechanical factors. 

Received 17 May 1994; accepted in final form 16 February 1995.
APS Manuscript Number A474-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.