Effects of Age on Cutaneous Circulatory Response to Direct Heat on the Forearm

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Abstract
To investigate the effects of age on the response of skin blood flow in the forearm to direct heat, three groups of 20 male subjects each —young (20–39 yr); middle-aged (40–59 yr) and older (60–79 yr) — consented to have skin blood flow measured in the forearm by a TSI Model 403 laser Doppler flowmeter. This instrument detects changes in red blood cell velocity (LDV) inflow-active vessels and the volume of red blood cells flowing through these vessels (LDO). With the forearm in a 30 °C water bath there were no significant between-group differences in LDV or LDO. Elevating bath temperature to 35 °C elicited a significant increase in LDO in all three groups, but LDV did not significantly change. Increasing temperature to 40 °C elicited significant increases in both LDO and LDV with the former being of greater magnitude. At this temperature LDV values in both the middle-aged and older groups were significantly lower than those of the young subjects. Expressing the data during heating as percent change from 30 °C showed a significantly lower volume (LDO) response in the older group at 35 and 40 °C and a significantly lower LDV response at 40 °C for both the middle-aged and older subjects in comparison to the young group. It is concluded that aging decreases the response of cutaneous blood flow in the forearm to the direct effects of heat. The LDV data suggest that this is mediated by a reduced flow response of individual microvessels in middle-aged and older men. The LDO data suggest that, in addition, vessel recruitment is depressed in older individuals.