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 beta-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 degrees C and -8 degrees C. Healthy volunteers increased their submaximal exercise time by 20% (1,353 +/- 455 [20 degrees C] vs 1,635 +/- 475 seconds [-8 degrees C]; p <0.05), whereas patients with CHF exhibited a 21% decrease in exercise time (1,182 +/- 549 [20 degrees C] vs 931 +/- 524 seconds [-8 degrees C]; p <0.05) at -8 degrees C. Beta blockers increased submaximal exercise duration at 20 degrees C (+261 +/- 617 seconds; p <0.05) and -8 degrees C (+374 +/- 729 seconds; p <0.05). Norepinephrine increased to a greater extent at 4 minutes and at the time of exhaustion (at -8 degrees 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.