LIMB CONGESTION AND SYMPATHOEXCITATION DURING EXERCISE - IMPLICATIONSFOR CONGESTIVE-HEART-FAILURE

During static exercise, heart failure (HF) subjects activate the sympa thetic nervous system differently than normal controls. HF causes meta boreceptor desensitization with either enhanced mechanoreceptor activi ty or central command. In this report, we examined whether increased m uscle interstitial pressure, as seen in HF, augments other neural syst ems. We measured muscle sympathetic nerve activity (MSNA; peroneal ner ve) in 10 normals during static exercise (40% maximal voluntary grip) and posthandgrip circulatory arrest (PHG-CA). This was repeated after venous congestion (VC; cuff inflation to 90 mmHg). VC increased forear m volume (plethysmography) by 4.7%. MSNA responses to exercise were gr eater after VC (150.5+/-41.8 vs. 317.3+/-69.9 arbitrary units; P < 0.0 1). However, MSNA responses during PHG-CA were not affected by VC, and P-31 nuclear magnetic resonance (n = 5) demonstrated no effect of VC on pH or H2PO4-. Similar effects of VC on MSNA were noted after ischeM iC exercise (n = 7), excluding flow alterations as the explanation. VC probably sensitized mechanically sensitive afferents since MSNA durin g involuntary biceps contractions increased after VC (n = 6), and skin sympathetic nerve responses during handgrip, an index of central comm and, were not increased by VC (n = 6).