Implications of sympathetic activation for objective versus self-reported daytime sleepiness in obstructive sleep apnea.

Study Objectives: Objective excessive daytime sleepiness (EDS) is associated with systemic inflammation and a higher risk of cardiometabolic morbidity in obstructive sleep apnea (OSA). We hypothesized that OSA with objective EDS is associated with higher levels of sympathetic nerve activity (SNA) when compared with self-reported EDS. We, therefore, examined the associations between objective and self-reported EDS with SNA in patients with OSA.

Methods: We studied 147 consecutive male patients with OSA from the institutional sleep clinic. Objective EDS and self-reported EDS were defined based on Multiple Sleep Latency Test (MSLT) latency ≤ 8 minutes and Epworth Sleepiness Scale (ESS) > 10, respectively. Twenty-four-hour urinary norepinephrine was used for assessing SNA. Blood pressure (BP) was measured both in the evening and in the morning.

Results: Twenty-four-hour urinary norepinephrine was significantly higher in patients with OSA with objective EDS compared with those without objective EDS (p = 0.034), whereas it was lower in patients with OSA with self-reported EDS compared with those without self-reported EDS (p = 0.038) after adjusting for confounders. Differences in the sympathetic drive were most striking in those with an objective but not self-reported EDS versus those with self-reported but not objective EDS (p = 0.002). Moreover, shorter MSLT latency was significantly associated with higher diastolic BP (β = -0.156, p = 0.049) but not systolic BP. No significant association between ESS scores and BP was observed.

Conclusions: Objective, but not self-reported EDS, is associated with increased SNA and diastolic BP among males with OSA, suggesting that objective EDS is a more severe phenotype of OSA that is accompanied by higher sympathetic drive, higher BP, and possibly greater cardiovascular morbidity and mortality.