FOREARM COMPRESSION DURING EXERCISE INCREASES SYMPATHETIC-NERVE TRAFFIC

Previously, we showed that forearm venous congestion augmented muscle sympathetic nerve activity (MSNA) during static exercise. We postulate d that venous congestion increased interstitial pressure, sensitizing mechanoreceptor afferents that led to a greater sympathoexcitation dur ing exercise. In this study, we tested the hypothesis that forearm com pression (FC) would increase interstitial pressure and selectively sti mulate mechanically sensitive afferents. We measured MSNA during 2 min of ischemic static exercise (40% maximal voluntary contraction) and 2 min of posthandgrip circulatory arrest. Exercise was performed again after 5 min of FC induced by inflation of a forearm cuff to 90 mmHg (n = 6) and 110 mmHg (n = 7). FC without exercise had no effect on any o f the hemodynamic variables. MSNA and mean arterial blood pressure res ponses were not augmented when exercise was performed with FC at 90 mm Hg. However, static exercise coupled with FC at 110 mmHg did augment t he reflex responses to static exercise (changes in MSNA before and aft er FC were 277 +/- 58 and 503 +/- 82 arbitrary units, respectively, P < 0.02; changes in mean arterial pressure before and after FC were 35 +/- 4 and 41 +/- 5 mmHg, respectively, P < 0.003). These responses wer e probably not due to greater metaboreceptor stimulation, since postha ndgrip circulatory arrest responses were unaffected by FC. We postulat e that FC sensitizes mechanoreceptors, leading to greater sympathoexci tation during exercise.