The reduction in vascular resistance with elevation of intravascular pressure is principally due to passive distention of the vascular bed rather than anomalous blood viscosity.
Passive distention, not viscosity, drives pressure-induced resistance reduction in animal models; extends vascular physiology but leaves open human translation.
Observations were made on an isolated hind leg preparation of dogs, perfused with blood and various homogeneous perfusates. A wide range of intravascular pressures were used while a constant arteriovenous pressure gradient was maintained. It was found that parallel increases in arterial and venous pressures result in a reduction in resistance to blood flow. A similar change in resistance is observed when more homogeneous perfusates are employed. Therefore, under the conditions of these experiments, the reduction in resistance with elevation of intravascular pressure must be ascribed principally to passive distention of the vascular bed.
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Levy et al. (1956) studied this question.
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