Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA171

Poster Communications

Effects of temperature on repeated local skin heating induced desensitization in humans

S. Thomas1, H. Jones1, D. Thijssen1,2, D. A. Low1

1. Research Institute of Sports & Exercise Sciences, Liverpool John Moores University, Brighouse, West Yorkshire, United Kingdom. 2. Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands.

Thermoregulatory and cutaneous thermosensory reflexes are vital for survival (1). Rapid skin heating induces a biphasic microvascular hyperaemic response: an initial axon-mediated vasodilation, followed by a sustained increase and plateau of skin blood flow (2). Skin heating responses maybe subject to desensitization phenomenon, whereby a previously heated site has reduced microvascular function on subsequent thermal provocation (3), but findings are mixed (4). Desensitization has important implications for persons undergoing repeated thermal stress, such as firefighters or athletes in heat-based competitions, as well as for methodological considerations. A key element of desensitization maybe the magnitude of heating employed. The aim of this study was to investigate the effect of temperature on skin microvessel responses to repeated local heating. 12 participants (1 female) had forearm skin microvessel function assessed by laser Doppler flowmetry (LDF) responses to 3 site-specific levels of local heating: 36°C, 39°C, and 42°C (PRE). Participants were exposed to 2 more bouts of local heating 30 and 90 minutes later (POST30, POST90). Skin blood flux was indexed as cutaneous vascular conductance (CVC=LDF flux/mean arterial pressure, PU.mmHg-1), normalised to maximal vasodilation (44°C heating at end of each stage of testing, %CVCmax). Data were compared by ANOVA per timepoint (baseline/axon peak/axon nadir/plateau/maximum) with Bonferroni correction. Local skin heating responses were graded according to target temperature at each stage of testing (Table 1). There was an increased axon-peak response POST30 at 42°C (vs PRE, P=0.005), and a decreased axon-nadir at 42°C (vs PRE, P=0.005). There were no changes to axon reflex responses at 36°C or 39°C POST30 (P>0.05 both). There was a reduced plateau response POST30 at all 3 sites (vs PRE: 42°C, P<0.001; 39°C, P=0.003; 36°C, P<0.001). POST90 plateau responses were also attenuated, but only significantly at 42°C (vs PRE, P=0.002). Repeated local skin heating causes an altered axon reflex response at temperatures >40°C, and reduces endothelium-dependent ‘plateau' vasodilation at temperatures as low as 36°C, indicating cutaneous heat dissipation maybe impaired during subsequent exposure to elevated skin temperature.

Where applicable, experiments conform with Society ethical requirements