Abstract 2184: Altered Firing Pattern Of Single-unit Sympathetic Vasoconstrictor Fibers During Exercise In Chronic Heart Failure
Background: Although sympathetic activation in chronic heart failure (CHF) is greatly increased under resting conditions, the response to exercise remains controversial. We previously demonstrated that single-unit muscle sympathetic nerve activity (MSNA) reflected the pure sympathetic response to physiologic stress. The purpose of this study was to determine whether the response of single-unit MSNA to exercise was augmented in CHF, and, if so, whether the sympathoexcitation pattern of single-unit MSNA was altered.
Methods and results: The discharge behaviors of single-unit MSNA during handgrip exercise (30% maximum voluntary contraction for 3min) were examined in 13 CHF patients (NYHA II-III) and 11 age-matched healthy control subjects. Baseline value of single-unit MSNA was significantly increased in CHF patients compared to healthy subjects (44.4±3.5 spikes/min vs. 23.2±2.0 spikes/min, respectively; p<0.05). Multiunit and single-unit MSNA were significantly augmented by Handgrip exercise in both groups. The absolute change of multiunit MSNA was similar between two groups. However, the augmentation of single-unit MSNA in CHF patients was significantly greater than that in healthy subjects (21.1±2.2 spikes/min vs. 8.3 ±1.2 spikes/min, respectively, p<0.01). The firing patterns of single-unit MSNA within one burst were similar in both groups under resting conditions. However, these patterns were augmented toward multiple spikes during exercise in CHF patients (P<0.05).
Conclusions: The responses of single-unit MSNA to exercise were augmented in CHF patients. These results indicated that the augmented reflexes of single-unit sympathetic activity during exercise might be different in patients with CHF with high levels of resting sympathetic nerve activity, which may contribute to further sympathoexcitation during exercise.