Relationship between the body position-specific apnea-hypopnea index and subjective sleepiness.

BACKGROUND It is well known that the sleeping position influences the rate of apnea-hypopnea events; however, whether events in one position may have more influence on daytime sleepiness than events in another position has not been thoroughly investigated. OBJECTIVES We retrospectively examined the relationship between the body position-specific apnea-hypopnea index (AHI) and daily sleepiness. METHODS We assessed the sleeping body position, the body position-specific AHI and the Epworth Sleepiness Scale (ESS) in a total of 699 patients who were referred for suspected obstructive sleep apnea-hypopnea syndrome (OSAHS) and underwent diagnostic polysomnography. RESULTS For all subjects, only the lateral position-specific AHI (L-AHI) showed a weak but significant correlation with the ESS (r = 0.102; p < 0.05). For mild-to-moderate OSAHS patients, there was no correlation between the ESS and the AHI at any position. For severe OSAHS patients, the ESS showed a closer correlation with the L-AHI (r = 0.266; p < 0.001) than with the supine position-specific AHI (S-AHI; r = 0.141; p < 0.05). In a subgroup analysis, divided into positional and non-positional severe OSAHS patients, the correlation coefficients also identified a link between the L-AHI and the ESS. Finally, a multiple linear regression analysis indicated that the ESS was better explained by the L-AHI than by the S-AHI in severe OSAHS patients. CONCLUSION The L-AHI is considered to have a stronger influence on daytime sleepiness than the S-AHI in Japanese patients with severe OSAHS.