The cutaneous microcirculation of the forearm in young and old subjects

Previous studies have shown a reduced cutaneous circulatory response to direct heat stress in the forearm circulations of older (60 to 80 year) subjects. The purpose of this study was to test the hypothesis that this aging effect is due to a reduced ability of the cutaneous microvessels in the forearm to respond to direct heat. Two groups of male subjects consented to participate; a group of 15 young individuals (Y; 20-39 year) and a group of 11 older (O; 60-79 year) individuals. The subjects rested in a supine position with the right forearm situated on the stage of a Leitz epiilumination microscope which was used to view the superficial cutaneous microvessels. The width of the red cell column (WRC), an index of vascular diameter, and the blood cell velocity (BCV) within the microvessels were measured by videomicroscopy at the presenting skin temperature (Ts) of 32 degrees, and then again after Ts had been elevated to 35 degrees then 40 degrees. At a Ts of 32 degrees, WRC and BCV for the Y group, respectively, averaged 6.6 microns and 0.22 mm/sec. Corresponding averages for the O subjects were 8.4 microns and 0.17 mm/sec. Between-group differences were not significant. At a skin temperature of 40 degrees, BCV was significantly higher compared to that at 32 degrees and 35 degrees for both groups (P less than 0.05); whereas, WRC did not significantly change. There were no significant between-group differences in BCV at the higher two temperatures. These results argue against a diminished blood flow response of superficial microvessels being responsible for the reduced cutaneous circulatory response to heat stress in older individuals.