Impact of heart failure and exercise capacity on sympathetic response to handgrip exercise

Peak oxygen uptake ((V) over dotO(2 peak)) in patients with heart failure ( HF) is inversely related to muscle sympathetic nerve activity (MSNA) at res t. We hypothesized that the MSNA response to handgrip exercise is augmented in HF patients and is greatest in those with low (V) over dotO(2 peak). We studied 14 HF patients and 10 age-matched normal subjects during isometric [30% of maximal voluntary contraction (MVC)] and isotonic (10%, 30%, and 5 0% MVC) handgrip exercise that was followed by 2 min of posthandgrip ischem ia (PHGI). MSNA was significantly increased during exercise in HF but not n ormal subjects. Both MSNA and HF levels remained significantly elevated dur ing PHGI after 30% isometric and 50% isotonic handgrip in HF but not normal subjects. HF patients with lower (V) over dotO(2 peak) (<56% predicted; n = 8) had significantly higher MSNA during rest and exercise than patients w ith (V)over dotO(2 peak) > 56% predicted (n = 6) and normal subjects. The m uscle metaboreflex contributes to the greater reflex increase in MSNA durin g ischemic or intense nonischemic exercise in HF. This occurs at a lower th reshold than normal and is a function of (V) over dotO(2 peak).