Dimensions of sleepiness and their correlations with sleep-disordered breathing in mild sleep apnea

OBJECTIVE: There are many ways of assessing sleepiness, which has many dimensions. In patients presenting a borderline apnea-hypopnea index (AHI, expressed as events/hour of sleep), the mechanisms of excessive daytime sleepiness (EDS) remain only partially understood. In the initial stages of sleep-disordered breathing, the AHI might be related to as-yet-unexplored EDS dimensions.

METHODS: We reviewed the polysomnography results of 331 patients (52% males). The mean age was 40 +/- 13 years, and the mean AHI was 4 +/- 2 (range, 0-9). We assessed ten potential dimensions of sleepiness based on polysomnography results and medical histories.

RESULTS: The AHI in non-rapid eye movement (NREM) stage 1 sleep (AHI-N1), in NREM stage 2 sleep (AHI-N2), and in REM sleep (AHI-REM) were, respectively, 6 +/- 7, 3 +/- 3 and 10 +/- 4. The AHI-N2 correlated significantly with the greatest number of EDS dimensions (5/10), including the Epworth sleepiness scale score (r = 0.216, p < 0.001). Factor analysis, using Cronbach's alpha, reduced the variables to three relevant factors: QUESTIONNAIRE (alpha = 0.7); POLYSOMNOGRAPHY (alpha = 0.68); and COMPLAINTS (alpha = 0.55). We used these factors as dependent variables in a stepwise multiple regression analysis, adjusting for age, gender, and body mass index. The AHI-N1 correlated significantly with POLYSOMNOGRAPHY (beta = -0.173, p = 0.003), and the AHI-N2 correlated significantly with COMPLAINTS (beta = -0.152, p = 0.017). The AHI-REM did not correlate with any factor.

CONCLUSIONS: Our results underscore the multidimensionality of EDS in mild sleep apnea.