A quantitative assessment of skin blood flow in humans

Various aspects of skin blood flow (SkBF) in human beings have been studied experimentally for more than seven decades. While reasonably complete phenomenological descriptions of individual factors have emerged from those investigations, little effort has been devoted to assembling the component parts into a coherent description of the entire system. This paper describes an effort to do that. Although the result is essentially a mathematical model of human SkBF, the model is firmly based on empirical data and not merely an abstract theoretical construct. We found that experimental data for human forearm blood flow (FBF) from many sources are well represented by an equation in which the rate of cutaneous blood flow (qs) is defined by the equation qs = qs,r AVD × CVCM × CVCL × CVCE. The coefficient qs,r is the perfusion rate at a reference state, and the four component factors are defined as follows: AVD defines centrally mediated active vasodilation as a function of central temperature (Tc), mean skin temperature $$({\bar{T}}_{{\rm s}}),$$ and intensity of exercise $$({\dot{V}}_{{\rm O}_2});$$ CVCM defines reflexly mediated cutaneous vasoconstriction as a function of $${\bar{T}}_{{\rm s}};$$ CVCL defines locally mediated cutaneous vasoconstriction as a function of local skin temperature (Ts); and CVCE defines the effect of exercise on cutaneous vasoconstriction and mean arterial pressure. The definition of each component function is based on experimental data. Two conclusions are particularly significant. One is that the study provides a rational explanation, based on the role of $${\bar{T}}_{{\rm s}},$$ for previously disparate opinions about the non-thermal effect of exercise on active cutaneous vasodilation. The other is that it establishes that the four factors combine multiplicatively, and not additively, as previous investigators have suggested.