Search

Background:In heart failure (HF), muscle sympathetic nerve activity (MSNA) is markedly increased at resting condition, but reaction to sympathoexcitation is controversial. Recently, a technique for recording from individual vasoconstrictor nerves (single MSNA) was described and it can evaluate the frequency of pure sympathetic firing. In this study, we investigated the frequency of pure sympathetic firing by recording single MSNA to determine the accurate physiological responses of sympathoexcitation. Methods and Results:Ten HF patients (NYHA II∼III) and 8 age matched healthy subjects were studied. Single MSNA and multiunit MSNA were measured before and during handgrip exercise (HG) at 30% of maximum voluntary contraction for 3 minutes. The increases of multiunit MSNA during HG was not different between HF patients and healthy subjects (6.8 bursts/min vs 7.3 bursts/min, NS). However, the increases of single MSNA in HF patients was greater than that in young healthy subjects (25.0 spikes/min vs 9.3 spikes/min, p < 0.01) and augmented firing pattern was toward multiple spikes per one cardiac interval. Conclusions:These results suggest augmented sympathetic response to exercise in HF patients may be caused by increased single MSNA response, but not multiunit MSNA.