The effect of repeated bouts of hyperaemia on sensory nerve-mediated cutaneous vasodilatation in humans.

PURPOSE: To investigate cutaneous sensory nerve contribution to hyperaemia following chronic shear stress training.

METHODS

Eleven males underwent a shear stress intervention (forearm occlusion 5 s, rest 10 s) for 30 min, 5 times·week-1 for 6 weeks on one arm, the other was an untreated control. Skin blood flow was measured using laser-Doppler flowmetry, and sensory nerve function was assessed with and without blockade with EMLA cream in response to 3 levels of local heating (39, 42, and 44 °C) and post-occlusive reactive hyperaemia (PORH).

RESULTS

In response to local heating, EMLA treatment significantly delayed the onset of vasodilatation (p < 0.001), time-to-peak (p < 0.001), time to 39 °C (p < 0.02), time to 42 °C (p < 0.006), but not time to 44 °C (p > 0.2). EMLA treatment also increased time-to-peak for PORH (p ≤ 0.01). In the experimental limb after 6 weeks, both onset time and time to peak were shorter in response to local heating at the untreated and EMLA-treated sites (all p < 0.001). There were no changes in time-to-peak for PORH at the untreated and EMLA-treated sites (p ≥ 0.4); however, the peak PORH response was reduced with EMLA treatment (p ≤ 0.03). The 6-week intervention increased the peak PORH at the untreated sites (p < 0.001) but not at EMLA-treated (p > 0.05) sites. Comparing the control limb before and after 6 weeks, no differences in responses occurred at either the untreated skin sites (p ≥ 0.9) or the EMLA-treated sites (p ≥ 0.9).

CONCLUSIONS

Sensory nerve blockade attenuated the improvements in cutaneous vascular responses to thermal hyperaemia and PORH following chronic exposure to shear stress. These data demonstrate an important role for sensory nerve function in the initiation of vasodilatation to both PORH and thermal hyperaemia, in both the time to onset and the magnitude of vasodilatation.