ELASTIC POROUS TUBE MODEL OF REACTIVE HYPEREMIA

Reactive hyperaemia is the term given to the temporary increase in blo od flow that follows release of an occlusion of the arterial supply. M easurement of reactive hyperaemia in the leg below the knee is useful in assessment of the vascular system, as resting flows remain unaffect ed even in the presence of quite severe occlusive arterial disease. An elastic porous tube representation of the vascular system is used to develop equations for the variation of the mean pressure, flow and ves sel calibre in the vascular system, the tube represents the arteries a nd large arterioles, which respond passively to changes in pressure. L eakage through the tube walls represents flow into the small arteriole s, which respond actively to the rise in pressure following release of the occlusion by constricting (the myogenic response). The capillarie s are represented by rigid tubes, and the venous system is represented by a single compliant vessel. The model predicts variations in the fl ow, pressure and vessel calibre that are in agreement with experimenta l observations, and identifies that the pressure gradient is important in determining the initial transient increase in the flow following r elease of the occlusion. The subsequent development in the flow is gov erned by the small arteriolar flow, which is determined by the magnitu de and duration of the myogenic response.