Inverse Relationship of Subjective Daytime Sleepiness to Sympathetic Activity in Heart Failure Patients with Obstructive Sleep Apnea.

Abstract BACKGROUND:Patients with heart failure (HF) and obstructive sleep apnea (OSA) are less sleepy than patients with OSA, but without HF. Furthermore, unlike the non-HF population, in the HF population the degree of daytime sleepiness was not related to the apnea-hypopnea index (AHI). The sympathetic nervous system plays a critical role in alertness. HF and OSA both increase sympathetic nervous system activity (SNA) during wakefulness. We hypothesized that in HF patients with OSA, the degree of subjective daytime sleepiness will be inversely related to SNA. METHODS:Daytime muscle SNA (MSNA) was recorded in HF patients with OSA. Subjective daytime sleepiness was assessed by the Epworth Sleepiness Scale (ESS). RESULTS:We studied 27 patients with HF and OSA and divided them into two groups based on the median ESS score: a less sleepy group with an ESS score <6 (n=13) and a sleepier group with an ESS score ≥6 (n=14). The less sleepy group had higher MSNA (82.5±9.9 vs 69.3±18.6 bursts per 100 cardiac cycles, p=0.037) and a longer sleep onset latency (33±29 vs 14±13 minutes, p=0.039) than the sleepier group. The ESS score was inversely related to MSNA (r = -0.63, p<0.001), but not to the AHI, arousal index or indices of oxygen desaturation. CONCLUSIONS:In patients with HF and OSA, the degree of subjective daytime sleepiness is inversely related to MSNA. This relationship is likely mediated via central adrenergic alerting mechanisms. These findings help to explain the previously reported lack of daytime hypersomnolence in patients with HF and OSA.