REFLEX PERIPHERAL VASOCONSTRICTION IS DIMINISHED IN OLDER MEN

The purpose of this study was to compare reflex control of limb blood flow in healthy young (Y; 26 +/- 2 yr) and older (O; 61 +/- 2 yr) men during whole body cooling under resting conditions. To better isolate the effect of chronological age, the two age groups (n = 6 per group) were closely matched for maximal oxygen uptake, body surface area, ski nfold thickness, and fat-free weight. Subjects sat in an environmental ly controlled chamber clad in standardized (0.6-clo) light cotton clot hing at a dry-bulb temperature (T-db) of 28 degrees C. After 30 min, T -db was decreased by 2 degrees C every 5 min until T-db = 10 degrees C , where it was held constant for the remainder of the 120-min session. Esophageal and mean skin temperatures were monitored continuously. Fo rearm blood flow (FBF) was measured every 5 min by venous occlusion pl ethysmography by using a mercury-in-Silastic strain gauge while arm te mperature between the wrist and elbow was clamped at 37.2 +/- 0.1 degr ees C by localized warm air heating. In this way, limb vasoconstrictio n was driven solely by thermoregulatory reflexes and not by direct eff ects of localized cooling. Mean skin temperature decreased at a simila r rate and to a similar extent (by similar to 6 degrees C over a 2-h p eriod) in both age groups, whereas esophageal temperature was relative ly unaffected. In response to the local heating, the Y group maintaine d a significantly higher FBF than did the O group during the initial 3 0 min but decreased FBF during the cooling phase at a greater rate and to a greater extent than did the O group, leading to a significantly lower FBF during the final 30 min (at T-db = 10 degrees C). Because th ere was no age difference in the mean arterial pressure response, simi lar effects of age were seen on forearm vascular conductance (FBF/mean arterial pressure). It was concluded that older men have a diminished reflex limb vasoconstrictor response to skin cooling. Furthermore, th is difference in control of peripheral blood flow appears to be relate d to age per se; i.e., it is not a reflection of age-related differenc es in maximal oxygen uptake or body composition.