Differential vasodilatory responses to local heating in facial, glabrous and hairy skin

Background and aims: Local heating induces biphasic cutaneous vasodilation in non-glabrous skin of the forearm. However, little data exist in other skin regions, despite the prevalence of facial flushing disorders. We hypothesized that facial skin will have greater initial peak responses to local heating than forearm skin because of neural differences between sites and, furthermore, axon reflex vasodilation will be eliminated in facial sites with sensory blockade. Methods: Skin blood flow (laser-Doppler flowmetry) responses of healthy, non-obese subjects to local heating (32-42°C in ~5 min, held 40 min) in the forehead (n = 22), cheek (n = 22), forearm (n = 22) and palm (n = 13) were expressed as percentage of maximum cutaneous vascular conductance (CVC; flux/mean arterial pressure). In an additional group (n = 7), sensation was blocked (topical prilocaine-lidocaine) prior to the local heating protocol. Results: Prior to heating, CVC differences were noted (forearm = 10 ± 3, cheek = 19 ± 3, forehead = 16 ± 1 and palm = 65 ± 11%CVC; P<0·05). Initial peak CVC was similar between forehead, cheek and forearm (85 ± 3, 92 ± 2, and 91 ± 6%CVC, respectively), but elevated in the palm (120 ± 8%CVC; P<0·05). Compared to facial control sites, sensory blockade delayed increases in both cheek and forehead (P<0·05) CVC but did not change magnitude of the biphasic response (P>0·05). Conclusions: These data indicate that facial skin initial CVC peaks to local heating are similar to non-glabrous skin. In contrast to forearm responses, facial topical sensory blockade does not abate axon reflex responses to local heating. Palm skin data indicate that maximal skin blood flow is not obtained during local heating as it is in non-glabrous skin.