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1 Surgery, University of Sherbrooke, Sherbrooke, Quebec, Canada
2 Pediatrics and Physiology, University of Sherbrooke, Sherbrooke, Quebec, Canada
3 Surgery, University of Sherbrooke, Sherbrooke, Quebec, Canada; Pediatrics and Physiology, University of Sherbrooke, Sherbrooke, Quebec, Canada
* To whom correspondence should be addressed. E-mail: Jp.Praud{at}USherbrooke.ca.
We tested the hypotheses that active upper airway closure during induced central apneas in non-sedated lambs 1) is complete and occurs at the laryngeal level, and 2) is not due to stimulation of the superior laryngeal nerves (SLN). Five newborn lambs were surgically instrumented to record thyroarytenoid muscle (TA, a glottal constrictor) electrical activity (EMG) with supra and sub-glottal pressures. Hypocapnic and non-hypocapnic central apneas were induced before and after SLN sectioning in the 5 lambs. A total of 174 apneas were induced, 116 before and 58 after SLN section. Continuous TA EMG activity was observed in 88 % of apneas before SLN section and in 87 % of apneas after SLN section. A trans-glottal pressure different from zero was observed in all apneas with TA EMG activity, with a mean sub-glottal pressure of 4.3 ± 0.8 cmH20 before and 4.7 ± 0.7 cmH20 after SLN section. Supra-glottal pressure was consistently atmospheric. Sectioning of both SLN had no effects on the results. We conclude that upper airway closure during induced central apneas in lambs is active, complete and occurs at the glottal level only. Consequently, a positive sub-glottal pressure is maintained throughout the apnea. Finally, this complete active glottal closure is independent from laryngeal afferent innervation.
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