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Effects of hypoxia and hypercapnia on nonnutritive swallowing in newborn lambs

¹Neonatal Respiratory Research Unit, Departments of Pediatrics and Physiology, ⁵Department of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, Quebec, Canada; ²Institut National de la Santé et de la Recherche Médicale, U642; ³Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1; and ⁴Département de Médecine de l'Enfant et de l'Adolescent, Néonatologie, Centre Hospitalier Universitaire Rennes, Rennes, France

Submitted 20 March 2007 ; accepted in final form 7 July 2007

The aim of the present study was to investigate the effect of hypercapnia and hypoxia on apnea and nonnutritive swallowing (NNS) frequency, as well as on the coordination between NNS and phases of the respiratory cycle in newborn lambs, while taking into account the potential effects of states of alertness. Six lambs were chronically instrumented for recording electroencephalogram, eye movements, diaphragm and thyroarytenoid muscle (a glottal adductor) activity, nasal airflow, and electrocardiogram. Polysomnographic recordings were performed in nonsedated lambs exposed to air (control), 10% O₂, and 5% CO₂ in a random order at 3, 4, and 5 days of age. Although hypercapnia decreased apnea frequency in wakefulness and active sleep (P = 0.002 vs. air and hypoxia), hypoxia had no significant effect on apnea. In addition, although hypercapnia increased NNS frequency during wakefulness and quiet sleep (P < 0.005 vs. air and hypoxia), hypoxia tended to decrease NNS frequency. Finally, only hypercapnia altered NNS-breathing coordination by increasing NNS at the transition from inspiration to expiration (ie-type NNS; P < 0.001 vs. air and hypoxia). In conclusion, whereas hypercapnia increases overall NNS frequency by specifically increasing ie-type NNS, hypoxia has the inverse tendency. Results were identical in all three states of alertness.

control of breathing; apneas; thyroarytenoid muscle; sleep; radiotelemetry