The effect of increased tissue pressure on blood flow.

Theoretical consideration of the factors involved in maintaining vascular equilibrium and experimental evidence in animals and man indicate that at high tissue pressures there may be a sharp decline in blood flow and, in certain situations, complete cessation of blood flow even at tissue pressures below mean arterial pressure. At least two mechanisms appear to be involved: active closure of small arterioles under vasomotor tone when transmural pressure is lowered, either by falls in intravascular pressure or rises in tissue pressure, and passive collapse of soft-walled capillaries when tissue pressure rises above intracapillary pressure. These mechanisms are likely to assume particular importance when tissues are surrounded by non-compliant fascia and may thus be involved in compartmental syndromes.