Figure 3. Arterial input pressure and flow.
A. Theoretical relationship between pressure and flow (black line) showing the autoregulation of vascular tone to sustain a constant blood flow despite varying arterial input pressures. The orange dashed lines illustrate how changes in vascular tone alter the relationship between instantaneous arterial input pressure and blood flow subject to autoregulation. The point at which arterioles spontaneously collapse (zero blood flow) limiting arterial pressure drop is referred to as the critical closing pressure (Pcc), which also varies with changes in vasomotor tone.
B. Theoretical vascular pressure profile throughout the circulatory tree. Mean arterial pressure (MAP) is constant for most of the arterial tree since larger arteries serve mainly as vascular capacitors holding stored blood under pressure. By contrast, vascular pressure drops rapidly once blood reaches smaller arteries that branch into arterioles and precapillary
sphincters. The vascular waterfall is approximated by the critical closing pressure (Pcc) mirroring how water flowing over a waterfall is unaffected by how far it falls once over the edge. Thus, the decline in pressure from arterioles to venules, or changes in downstream venous pressure, does not influence either arterial pressure or blood flow. Mean systemic filling pressure (Pmsf) represents the upstream pressure driving venous return
against a downstream central venous pressure (CVP).
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