[A case of sleep apnea syndrome with significant alteration of apnea index by sleep position].

An obese 37-year-old man (130% ideal body weight) was admitted to our hospital with the complaint of excessive daytime sleepiness. During all-night polysomnography, he showed predominantly obstructive sleep apnea and an apnea index (AI) of 57.5, and was diagnosed as having obstructive sleep apnea syndrome (OSAS). However, AI values calculated separately for the time in the supine position (AI-S) and in the lateral decubitus position (AI-L) were 82.4 and 5.9, respectively. Moreover, duration of apnea, lowest SaO2, and the quality of sleep were improved when sleeping in the lateral compared to the supine position. After weight reduction of 7 kg, AI in total decreased to 33.2, although AI-S was 77.3 and AI-L was 3.8. The improvement of AI in total to be due to a relative increase during sleep in the lateral position. These results suggest that in some OSAS patients, the sleep position should be taken into account in assessing the severity of the disease or in evaluating the effects of therapy. This study also suggests the efficacy of sleep position adjustment in the treatment of OSAS.