Effect of sympathetic nerve blockade on low‐frequency oscillations of forearm and leg skin blood flow in healthy humans

OBJECTIVE: To Examine the effect of inhibiting sympathetic function on cutaneous vasomotion in the forearm and leg. METHODS: Intradermal microdialysis fibers were placed in the forearm and leg, one as an untreated control (lactated Ringer's) and the other perfused with bretylium tosylate to block sympathetic nerves. Skin blood flow was monitored using laser Doppler flowmetry. Baseline was collected for 10 minutes before local skin temperature was increased to 42°C. Spectral analysis was performed using a Morlet wavelet. RESULTS: Bretylium tosylate increased skin blood flow during baseline in the forearm (d=1.6, P<.05) and leg (d=0.5, P<.05) and decreased skin blood flow at both sites during both the initial peak (d≥1.0, P<.05) and plateau (d≥0.8, P<.05). Treatment with bretylium tosylate reduced wavelet amplitude associated with neural activity during baseline in the forearm (d=1.6, P<.05) and leg (d=0.9, P<.05). This reduction in wavelet amplitude at bretylium tosylate-treated sites was also observed during the initial vasodilation to local heating in both the forearm (d=1.6, P<.05) and leg (d=1.4, P<.05) and during the sustained vasodilation in both the forearm (d=1.6, P<.05) and leg (d=1.2, P<.05). CONCLUSIONS: Our data support that the frequency band (0.021-0.052 Hz) associated with neurogenic activity appears to be correct having a large sympathetic component.