Effects of sex and heating rate on skin blood flow oscillations during local heating in young adults.

Objective: to explore sex and heating rate effects on frequency-domain indicators of the mechanisms modulating cutaneous vasodilation during local heating. Materials and Methods: In thirty young adults (21±3 years, 15 females), wavelet analysis of skin blood flux was assessed from laser-Doppler flux signals at the chest, abdomen, arm, forearm, thigh, and calf during rapid (33-42°C; 1°C·20 s^-1) and gradual (33-42°C; 1°C·5 min^-1) local skin heating. A wavelet transform using a Morlet mother wavelet was computed over the entire signal for each heating protocol (minimum 90 minutes) and 5-min time windows were subsequently isolated to determine responses during baseline and the 42°C heating plateau. Wavelet data were decomposed into metabolic, neurogenic, myogenic, respiratory, and cardiac frequency bands and presented as absolute and relative (normalized) amplitudes. Results: There was a significant sex by heating rate interaction for relative wavelet amplitude in the metabolic frequency band (P=0.003), which was 0.89-fold [0.82,0.98] lower (P=0.006) during rapid heating compared to gradual for females only. There were no significant interactions for the other frequency bands (all P≥0.054). Males showed greater absolute and relative amplitudes for neurogenic and myogenic bands compared to females (all P≤0.022). Rapid heating resulted in significantly lower absolute amplitudes for metabolic, neurogenic and cardiac bands compared to gradual heating (all P≤0.004). However, there was a significantly greater relative amplitude for the respiratory band during rapid heating compared to gradual (P=0.030). Conclusions: These exploratory findings highlight important sex and heating rate effects on wavelet-based indicators of the mechanisms modulating cutaneous vasodilation during local heating.