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Background and Objectives:OSAS is thought to be due to an excesive loss of muscle tone in the upper airway or an abnormal reflex regulation of uper airway function during slep. The aim of this study was to investigate the distribution of myosin heavy chain (MHC) isoforms of musculus uvulae in OSAS and snorers. Materials and Methods:Thirty seven patients included in the study underwent an uvulo-palato-pharyngoplasty (UPP ). All subjects had polysomnographic study before UPPP. ATPase stain at pH 9.4 were applied to muscle specimens obtained during UPPP. The numbers of MHC type I and II isoforms were counted. The patients were divided into thre groups according to their repiratory disturbance index (RDI):mild (0-20), moderate (21-40), severe (> 40). The diferences in the distribution of muscle fiber types were com-pared betwen these groups. The corelation betwen the distribution of the fibers and the body mas index / age / RDI / minimum O2 saturation / duration of slep apnea was investigated. Results:The mean percentages standard deviation of type I fibers acording to the severity of sleep apnea were as follows: 22.5± 3.2% in mild slep apnea group (n=15), 19.8± 2.3% in moderate slep apnea group (n=11), 17.5± 3.6% in severe slep apnea group (n=11). There were statistically significant differences in the distribution of MHC type I & II isoforms betwen mild group and moderate and / or severe group (p<0.05). There was statistically significant negative correlation betwen the proportion of type I fibers and RDI / duration of slep apnea (p<.01). We could not find meaningful corelation betwen the proportion of MHC type I isoforms and body mas index / age of the patients (p>.05). :The proportion of MHC type I isoforms in musculus uvulae was decreased according to the severity and duration of sleep apnea (p<.01). (Korean J Otolaryngol 2002;45:433-8)


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