Effect of Noradrenergic Blockade on Low‐frequency Oscillations of Human Skin Microcirculation.
Authors: Del Pozzi Andrew T , Mallette Matthew M , Martin Zachary T , Hodges Gary J 
Published: November 2023

Under normothermic conditions, the skin of the leg has higher sympathetic activity than the skin of the forearm; by contrast, after locally heating the skin to 42°C, the skin of the forearm has higher sympathetic activity. Work in human skin free flaps suggested that the vasomotion waves around 0.021–0.52 Hz corresponded to sympathetic activity.PURPOSENo study has verified the low‐frequency oscillations corresponding to sympathetic activity (0.021–0.052 Hz) in intact, healthy human skin. We hypothesized that sympathetic blockade would reduce the power in this low‐frequency band under normothermic conditions as well as in response to local skin heating. We examined the effects of acute, localized sympathetic nerve blockade on the low‐frequency oscillations of skin blood flow (SkBF) of the forearm and leg.METHODSNine volunteers (6 male, 3 female) had 2 sites on each limb prepared with microdialysis fibers, one perfused with Lactated Ringer's (study vehicle, CTRL) the other bretylium tosylate (BT). Local skin heaters and laser‐Doppler flux (LDF) probes were used to control local temperature and assess SkBF. Skin vasomotion data were analysed using wavelet analysis of the LDF signal. LDF data were collected for 10 min at 33°C and for 35 min after locally heating to 42°C. Data are presented as wavelet amplitude in arbitrary units (au).RESULTSBaselineIn the leg, neurogenic activity was reduced at BT treated sites (0.401 ± 0.049 au) compared to CTRL sites (0.569 ± 0.077 au; P = 0.04). There was no difference between the forearm CTRL and BT sites (P = 0.09). Nor were there differences between the forearm and leg CTRL (P = 0.69) and BT treated sites (P = 0.89).Onset of heatingNeurogenic activity was significantly higher at CTRL sites of the forearm (0.812 ± 0.091 au) and leg (0.854 ± 0.112 au) than at BT treated forearm (0.471 ± 0.064 au; P = 0.03) or leg (0.503 ± 0.094 au; P = 0.01). There was no difference between forearm and leg CTRL (P = 0.78) or BT treated sites (P = 0.75).Prolonged HeatingNeurogenic activity was higher at leg CTRL sites (1.272 ± 0.195 au) compared to BT treated sites (0.776 ± 0.152 au; P < 0.01). Forearm CTRL and the BT treated sites were not different (P = 0.08). Forearm CTRL and leg CTRL sites did not differ (P = 0.3) and neither did the BT treated sites (P = 0.57)CONCLUSIONThese data indicate that acute pharmacological blockade of the sympathetic nerves reduced the low‐frequency oscillations of SkBF of the forearm and leg reported to be associated with neural activity. During normothermia, neural activity was only reduced in the skin of the leg and not the forearm. Neurogenic activity was reduced at the onset of heating for both the forearm and leg at BT treated sites. Following prolonged local skin heating at 42°C, we found that neural activity of only the leg was reduced by noradrenergic blockade. These data suggest that the neural frequency band is representative of sympathetic activity. Furthermore, these data indicate that the skin of the leg has a higher noradrenergic component than that of the forearm which is congruent with previous in vivo human work.Support or Funding InformationBall State University Department of Kinesiology