Resting muscle sympathetic nerve activity and peak oxygen uptake in heart failure and normal subjects

Aims Exercise intolerance and increased efferent vasoconstrictor traffic to muscle are two characteristics of heart failure that have not been explici tly linked. We tested the hypothesis that peak oxygen consumption is invers ely related to resting muscle sympathetic nerve activity in heart failure. Methods and Results We recorded peroneal muscle sympathetic nerve activity in 17 treated heart failure patients (16 men.1 woman: mean ejection fractio n of 26.0 +/- 3.2% (SE)) and 17 age-matched healthy subjects (16 men, 1 wom an). Oxygen consumption was measured during cycle ergometry to maximal effo rt. In heart failure and normal subjects, mean peak oxygen consumption was 20.6 +/- 1.7 vs 32.2 +/- 2.6 ml.kg(-1).min(-1) (P<0.0001) and mean muscle s ympathetic activity was 49.3 +/- 2.8 vs 330 +/- 3.3 bursts.min(-1) (P<.0007 ) respectively. When age was accounted for by multiple regression analysis, there was a significant relationship between peak oxygen consumption and b urst frequency in heart failure (P<0.02) but not in healthy subjects. The p ercent of predicted peak oxygen consumption achieved (based on age, sex and body size) was inversely related to muscle sympathetic nerve burst frequen cy in heart failure (r=-0.71, P<0.0014) but not in normal subjects (r=-0.44 , P<0.08; P<0.0001 for this comparison). Conclusion Reduced exercise capacity in heart failure is related to increas ed efferent sympathetic traffic to calf muscle. These observations are cons istent with the concept of a peripheral neurogenic limit to exercise in hea rt failure.