Effect of age on cutaneous vasomotor responses during local skin heating.

This study examined the effect of ageing on the low-frequency oscillations (vasomotion) of skin blood flow in response to local heating (LH). Skin blood flow was assessed by laser-Doppler flowmetry on the forearm at rest (33°C) and in response to LH of the skin to both 42°C and 44°C in 14 young (24±1years) and 14 older (64±1years) participants. Vasomotion was analyzed using a wavelet transform to investigate power of the frequency intervals associated with endothelial, neural, myogenic, respiratory, and cardiac activities of the laser-Doppler signal. Laser-Doppler flux increased in both groups with LH (both d>1.8, p<0.001). Endothelial activity increased in both groups following LH to 42°C (young d=1.4, p<0.001; older d=1.2, p=0.005) and 44°C (young d=1.4, p=0.001; older d=1.5, p=0.005). Endothelial activity was higher in the young compared to older group during LH to 42°C (d=1.4, p=0.017) and 44°C (d=1.5, p=0.004). In response to LH to 42°C and 44°C, neural activity in both groups was decreased (both groups and conditions: d>1.2, p<0.001). Myogenic activity increased in the younger group following LH to 44°C (d=1, p=0.042), while in the older group, myogenic activity increased following LH to 42°C (d=1.2, p=0.041) and 44°C (d=1.1, p=0.041). Respiratory and cardiac activities increased in both groups during LH to 42°C and 44°C (All: d>0.9, p<0.017). There were no differences in wavelet amplitude between younger and older in the neural (d=0.1, p>0.7), myogenic (d=0.3, p>0.7), respiratory (d=0.4, p>0.6), and cardiac (d=0.1, p>0.7) frequency intervals. These data indicate that LH increases cutaneous endothelial and myogenic activity, while decreasing neural activity. Furthermore, ageing reduces the increase in cutaneous endothelial activity in response to LH.