PHYSIOLOGICAL, METABOLIC, AND MUSCLE-FIBER TYPE CHARACTERISTICS OF MUSCULUS UVULAE IN SLEEP-APNEA HYPOPNEA SYNDROME AND IN SNORERS

Upper airway dilator muscles play an important role in the pathophysio logy of sleep apnea hypopnea syndrome (SAHS). The mechanical and struc tural characteristics of these muscles remain unknown. The aim of this study was to compare the physiologic, metabolic, and fiber type chara cteristics of one upper airway dilator muscle (musculus uvulae, MU) in 11 SAHS and in seven nonapneic snorers. The different analyses were d one on MU obtained during uvulo-palato-pharyngoplasty. Snorers and SAH S differed only in their apnea + hypopnea indices (11.5+/-5.9 and 34.2 +/-14.6/h, respectively, mean+/-SD). Absolute twitch and tetanic tensi on production of MU was significantly greater in SAHS than in snorers while the fatigability index was similar in the two groups. Protein co ntent and anaerobic enzyme activities of MU were significantly greater in SAHS than in snorers; no difference was observed for aerobic enzym e activities. The total muscle fiber cross-sectional area of MU was si gnificantly higher in SAHS (2.2+/-0.9 mm(2)) than in snorers (1.1+/-0. 7 mm(2)). The surface occupied by type IIA muscle fibers of MU was lar ger in SAHS (2.00+/-0.96) than in snorers (0.84+/-0.63 mm(2)). We conc lude that the capacity for tension production and the anaerobic metabo lic activity of MU are greater in SAHS than in snorers.