• Vincent Carrière, Danny Cantin, Stéphanie Nault, Charlène Nadeau, Nathalie Samson, Jennifer Beck, and Jean-Paul Praud.
• 1Neonatal Respiratory Research Unit, Departments of Pediatrics and Physiology, Université de Sherbrooke, Sherbrooke, QC, Canada. 2Keenan Research Centre for Biomedical Science and Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, ON, Canada. 3Department of Pediatrics, University of Toronto, Toronto, ON, Canada.
• Crit. Care Med. 2015 Aug 1; 43 (8): e296-303.

ObjectiveWe previously reported the development of an active inspiratory laryngeal narrowing against ventilator insufflations when inspiratory pressure is increased during nasal pressure support ventilation in lambs. The present study aimed to further understand the factors involved in this inspiratory laryngeal narrowing. More specifically, we tested the hypothesis that a short inspiratory pressure rise time or a low PaCO2 level promotes inspiratory laryngeal narrowing observed in nasal pressure support ventilation. The effect of hypoxia was also assessed.DesignProspective, randomized, interventional study.SettingAnimal research laboratory at the Faculty of Medicine and Health Sciences, Université de Sherbrooke, Canada.SubjectsThirteen lambs aged 4-5 days.InterventionsPolysomnographic recordings were performed in chronically instrumented lambs to study states of alertness, glottal muscle electrical activity, tracheal pressure, SpO2, and respiratory movements. Lambs were ventilated with progressively increasing levels of nasal pressure support ventilation (10/4, 15/4, and 20/4 cm H2O), using a broad range of inspiratory rise times from 0.05 to 0.4 s. Thereafter, either CO2 (PaCO2 = baseline value + 10 mm Hg) or N2 (PaO2 = 45-55 mm Hg) was added to the inspiratory line.Measurements And Main ResultsThe percentage of respiratory cycles with phasic inspiratory activity of glottal constrictor muscle was measured and compared between the various experimental conditions. The different inspiratory pressure rise times tested did not alter the phasic inspiratory activity of glottal constrictor muscle during nasal pressure support ventilation. By contrast, this activity was virtually abolished by increasing PaCO2 in all lambs. Finally, no alterations in the phasic inspiratory activity of glottal constrictor muscle during nasal pressure support ventilation were observed during hypoxia.ConclusionsActive inspiratory laryngeal narrowing during nasal pressure support ventilation is not altered by inspiratory rise times ranging from 0.05 to 0.4 s or by moderate hypoxia, whereas a moderate increase in PaCO2 abolishes this activity.

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