Background—Sympathetic activation and respiratory abnormalities may each be implicated in the pathophysiology of congestive heart failure (CHF). Chemoreflexes are an important mechanism regulating both sympathetic drive and breathing. We therefore tested the hypothesis that chemoreflex function is altered in CHF.

Methods and Results—We compared ventilatory, sympathetic, heart rate, and blood pressure responses to hypoxia, hypercapnia, and the cold pressor test in 9 patients with CHF and 9 control subjects matched for age and body mass index. Baseline muscle sympathetic nerve activity (MSNA) was higher in the patients with CHF compared with control subjects (47±8 versus 23±3 bursts per minute, P<0.01). During hypercapnia, patients with CHF had greater increases in minute ventilation (6.7±1.4 versus 2.7±0.9 L/min, P=0.03) and heart rate (7.0±2.1 versus 0.6±1.2 bpm, P=0.02). Despite higher ventilation, which inhibits sympathetic activity, the MSNA increase in patients with CHF was also greater than that in control subjects (58±12% versus 21±9%, P=0.03). Ventilatory, autonomic, and blood pressure responses to hypoxia and the cold pressor test in CHF patients were not different from those in control subjects.

Conclusions—Chronic heart failure is characterized by a selective potentiation of ventilatory and sympathetic responses to central chemoreceptor activation by hypercapnia.