Calculated thermal conductivities and heat flux in man

Using data compiled by the Brussels Cadaver Analysis Study on 13 unembalmed cadavers, this study examined the validity of assumptions often made concerning the role of the skin and adipose tissue layers in thermal insulation in vivo. Skin thickness was previously reported to vary from 0.35 to 2.55 mm, depending on the site of measurement and gender of the subject. Assuming a thermal conductivity of 0.70 x 10(-3) kcal/(cm.s-1.degree C-1) for the skin, heat flux across the skin would vary between site and gender in the order of 7.5 times, ranging from 0.16 to 1.20 kcal.min-1.degree C-1.m-2. Due to the negligible thermal gradient across the skin layer, however, this would be of little physiologic significance. Assumptions concerning the homogeneity of skin thickness across gender and measurement site when investigating thermal insulation of the peripheral tissues would not, therefore, influence the reported results significantly. However, it has recently been shown that the calculated lipid fraction of the adipose tissue layer varies according to a person's level of adiposity. Using a two-component model of adipose tissue, the predicted thermal conductivity (k) of the adipose tissue in the present sample was found to range from 0.50 to 0.97 x 10(-3) kcal/(cm.s-1.degree C-1), being significantly lower (P = 0.005) in the five most obese cadavers [6.66 +/- 0.45 x 10(-4) kcal/(cm.s-1.degree C-1)] than in the five most lean cadavers [8.22 +/- 0.93 x 10(-4) kcal/(cm.s-1.degree C-1)]. Adiposity level correlated significantly (r = 0.80; P < 0.01) with calculated k values, suggesting caution must be taken when assuming a single k for the adipose tissue layer when examining divergent populations (i.e., obese vs. thin).