Maximal skin vascular conductance in subjects aged 5-85 yr

This study examined maximal forearm skin vascular conductance (FVC(max)) as a function of age in 74 healthy male and female subjects ranging in age from 5 to 85 yr. The skin temperature of the left forearm was uniformly clamped at 42°C by spraying a fine mist of water over the surface. Forearm blood flow (FBF) was measured by venous occlusion plethysmography (Hg-in- Silastic strain gauge). After 60 min of heating, a reactive hyperemia maneuver was performed to verify that forearm skin blood flow was maximal by using laser Doppler flowmetry to isolate the skin component of FBF. The maximal FBF of each subject was then divided by mean arterial pressure to yield FVC(max) (in ml · 100 ml^-1 · min^-1 · 100 mmHg^-1), i.e., minimal resistance. The model that best fits the data was curvilinear, as described by FVC(max) = 13.1 + 86.9 (age^-0.75) (r² = 0.52, P < 0.001). The exclusion of subjects younger than 18 yr of age simplified the model to a linear fit with a slope of -0.16 conductance units/yr for adults. Interindividual variability remained constant across the entire age span. Once the age effect was considered, there were no significant effects of gender, adiposity, resting blood pressure, physical activity level, or body surface area on FVC(max).