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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Intermittent hypoxia reduces upper airway stability in lean but not obese Zucker rats

Departments of ¹Exercise and Nutrition Sciences, ²Physiology and Biophysics, and ³Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, State University of New York at Buffalo, Buffalo, New York; and ⁴Department of Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, The Ohio State University, Columbus, Ohio

Submitted 19 January 2007 ; accepted in final form 24 April 2007

Obstructive sleep apnea involves intermittent periods of airway occlusions that lead to repetitive oxygen desaturations. Exposure to chronic intermittent hypoxia (IH) in rats increases diurnal blood pressure and alters skeletal muscle physiology. The impact of IH on upper airway muscle function is unknown. We hypothesize that IH exposure increases upper airway collapsibility in rats due to alterations of the muscles surrounding the upper airway. Lean and obese rats were exposed to cyclic alterations in O₂ levels (20.6%-5%) every 90 s, 8 h/day for 6 days/wk for 12 wk. Following the exposure period, arterial pressure was recorded via the tail artery in conscious unrestrained rats. Mean arterial pressure was increased in lean IH but not in obese IH-exposed Zucker rats (P < 0.05). The pharyngeal pressure associated with airway collapse (P_crit) was measured under anesthesia during baseline conditions and then during supramaximal stimulation of the hypoglossal nerve (cnXII). Baseline P_crit was more positive (more collapsible) in lean but not obese rats following 12 wk of IH (P < 0.05), while supramaximal stimulation of cnXII increased airway stability (decreased P_crit) in both lean and obese Zucker rats following IH to levels that were similar to their respective room air controls. The in vitro peak tension and the expression of the individual myosin heavy chain isoforms from the upper airway muscles were unaltered following IH. We conclude that IH leads to increases in baseline collapsibility in lean Zucker rats exposed to IH by nonmyogenic mechanisms.

airway obstruction; sleep apnea; obesity; genioglossus