Muscle sympathetic nerve activity during wakefulness in heart failure patients with and without sleep apnea

Sympathetic activation and sleep apnea are present in most patients with symptomatic systolic heart failure (HF). Acutely, obstructive and central apneas increase muscle sympathetic activity (MSNA) during sleep by eliciting recurrent hypoxia, hypercapnia, and arousal. In obstructive sleep apnea patients with normal systolic function, this increase persists after waking. Whether coexisting sleep apnea augments daytime MSNA in HF is unknown. We tested the hypothesis that its presence exerts additive effects on MSNA during wakefulness. Overnight sleep studies and morning MSNA recordings were performed on 60 subjects with ejection fraction < 45%. Of these, 43 had an apnea-hypopnea index >= 15 per hour. Subjects with and subjects without sleep apnea were similar for age, ejection fraction, HF etiology, body mass index, blood pressure, and heart rate. Daytime MSNA was significantly higher in those with sleep apnea (76 +/- 2 versus 63 +/- 4 bursts per 100 heartbeats [mean +/- SEM], P = 0.005; 58 +/- 2 versus 50 +/- 3 bursts/min, P = 0.037), irrespective of its etiology (the mean difference for central sleep apnea was 17 bursts per 100 heartbeats; n = 14; P = 0.006; and for obstructive sleep apnea, 11 bursts per 100 heartbeats; n = 29; P = 0.032). In a subgroup (n = 8), treatment of obstructive sleep apnea lowered MSNA by 12 bursts per 100 heartbeats (P = 0.003). Convergence of independent excitatory influences of HF and sleep apnea on central sympathetic neurons results in higher MSNA during wakefulness in HF patients with coexisting sleep apnea. This additional stimulus to central sympathetic outflow may accelerate the progression of HF; its attenuation by treatment of sleep apnea represents a novel nonpharmacological opportunity.