Age-related changes in upper airway muscles morphological and oxidative properties

Obstructive sleep apnea (OSA) is a common disorder of the middle aged and e lderly. It results from the decrease in upper airway muscle (UAM) tone that occurs during sleep. It is unclear whether age-related changes in UAM coul d constitute a contributory mechanism to the increased prevalence of OSA wi th increasing age, and previous papers evaluating the effects of aging on U AM in rats reported conflicting results, In the present study, we compared, in four age groups of Wistar rats (6-24 months), fiber-type distribution, mean cross-sectional fiber area and succinate dehydrogenase optical density of dilating and non-dilating UAM, and the diaphragm. Succinate dehydrogena se optical density, a marker of oxidative capacity, decreased significantly after the age of 6 months in all muscles (except for the sternohyoid), par ticularly in the genioglossus, the main tongue protrudor. In this muscle, w e also found a significant decrease in type IIa and an increase in IIb fibe rs after the age of 18 months. Age-related changes in fiber-type distributi on in other muscles were mostly insignificant. Dilating UAM could not be di stinguished from their Don-dilating neighboring muscles by their histochemi cal properties or aging-related changes. The aging-related changes observed in the present study may decrease UAM endurance, particularly that of the main tongue protrudor, the genioglossus. (C) 2001 Elsevier Science Inc. All rights reserved.