Positional Dependency in Asian Patients With Obstructive Sleep Apnea and Its Implication for Hypertension

Objectives: To investigate the relationship of obstructive sleep apnea (OSA) with positional dependency and to identify its clinical implication in an Asian population. Design: Retrospective analysis. Setting: Academic tertiary referral center. Patients: A total of 1170 adults (1003 men and 167 women; mean [SD] age, 50.8[12.9] years) with OSA were included from February 1, 2004, through October 31, 2008. Intervention and Main Outcome Measures: All patients underwent full-night polysomnography. The anthropometric or polysomnographic variables between the patients with positional OSA (PPs) and those with non-positional OSA (NPPs) were characterized, and multivariate analysis was performed to find the determining factors of positional dependency. The prevalence of hypertension was also investigated. Results: Nearly 75% of the patients (874 [74.7%]) had positional dependency. Positional dependency was present in 87.0% of the patients with mild OSA (apnea hypopnea index [AHI], >= 5 but < 20), in 84.2% of those with mod-erate OSA (20 <= AHI < 40), and in 43.1% of those with severe OSA (AHI >= 40). The prevalence of PPs was 46.4% among severely obese patients (body mass index [BMI], >= 30, calculated as weight in kilograms divided by height in meters squared) and 82.7% among the nonobese patients (BMI < 25) and 74.6% among obese patients (25 <= BMI < 30). Multivariate analysis showed that the AHI was the most dominant variable that determined positional dependency, followed by the BMI. In the PP group, the percentages of deep sleep and rapid eye movement sleep were significantly greater compared with those in the NPP group. The Epworth Sleepiness Scale score was lower in the PP group. The prevalence of hypertension was 34.4% and 49.7% in the PP and NPP groups, respectively. Conclusions: This study demonstrates that the prevalence of PPs among Asians is almost three-fourths of the patients and that the AHI is the most dominant factor for determining positional dependency, followed by BMI. The PP group had lower BMI, a lower AHI, longer deep sleep, longer rapid eye movement sleep, and less daytime sleepiness than did the NPPs. The prevalence of hypertension was also affected by positional dependency.