Thermally-induced cutaneous vasodilatation in aging.

A decrease in heat-induced cutaneous vasodilatation has been implicated as the cause of increased heat stress in the elderly. We used laser Doppler techniques to study the skin blood flow response to local heat in 82 healthy volunteers. There were 39 young volunteers, mean age 29 +/- 1, and 43 elderly volunteers, mean age 76 +/- 1. There was minimal difference in skin blood flow at 35 degrees C between the two groups. In contrast, skin blood flow at 44 degrees C was significantly lower in the older subjects at nutritively perfused sites, such as the knee and elbow. However, there was no difference between the young and old groups in skin blood flow at the finger or toe pulp, sites with primarily arteriovenous anastomotic (AVA) flow. In the older subjects, the two components of skin blood flow, microvascular volume (VOL) and red blood cell velocity (VEL), were both decreased at 44 degrees C at nutritive sites, but not at AVA sites. Regression analysis demonstrated a linear fall in blood flow, VOL, and VEL with advancing age at nutritive sites at 44 degrees C. We conclude that thermally-induced cutaneous blood flow is reduced in older persons at nutritive capillary sites, but not at AVA sites.