Effects of cold exposure on submaximal exercise performance and adrenergic activation in patients with congestive heart failure and the effects of beta-adrenergic blockade (carvedilol or metoprolol)

Abstract

Patients with congestive heart failure (CHF) exhibit a decrease in maximal exercise capacity in response to a cold environment. The aim of this study was to further investigate the impact of cold exposure on submaximal exercise capacity, systemic adrenergic drive, and the effects of long-term β-adrenergic blockade on these parameters. Thirty-three patients with CHF, with exercise limited by dyspnea and left ventricular ejection fraction of 26 ± 4%, were randomized to receive metoprolol or carvedilol for 6 months. The observations were compared with 12 age-matched healthy volunteers. Maximal exercise performance with gas exchange analyses were assessed using a ramp protocol, and endurance capacity was measured using 2 constant-load exercise tests performed randomly at 20°C and −8°C. Healthy volunteers increased their submaximal exercise time by 20% (1,353 ± 455 [20°C] vs 1,635 ± 475 seconds [−8°C]; p <0.05), whereas patients with CHF exhibited a 21% decrease in exercise time (1,182 ± 549 [20°C] vs 931 ± 524 seconds [−8°C]; p <0.05) at −8°C. Beta blockers increased submaximal exercise duration at 20°C (+261 ± 617 seconds; p <0.05) and −8°C (+374 ± 729 seconds; p <0.05). Norepinephrine increased to a greater extent at 4 minutes and at the time of exhaustion (at −8°C) only in patients with CHF. Beta-adrenergic blockade caused no significant decrease in plasma norepinephrine levels. Patients with symptomatic CHF exhibited a significant decrease in submaximal exercise time in response to moderate cold exposure. Beta-blocker therapy with either metoprolol or carvedilol significantly increases submaximal exercise time and attenuates the impact of cold exposure on functional capacity.