Significance of critical closing pressures (starling resistors) in arterial circulation

Excerpt

Arterial pressure is the input pressure driving tissue blood flow. However, under most conditions organ blood flow is independent of arterial pressure. Tissue blood flow is proportional to local metabolic demand and can vary widely without any change in arterial pressure. Furthermore, changes in arterial pressure within physiologic limits do not alter tissue blood flow. The reason for these apparent incongruities derive from the determinants of organ blood flow. Tissues autoregulate their levels of delivered oxygen to meet their metabolic demand. As tissue metabolic demand increases, as occurs in the gut during digestion, the brain with cognition or muscle with exercise, local O₂ consumption increases to sustain adequate ATP flux. This stimulates the local capillary endothelia in a retrograde fashion to decrease upstream vasomotor tone [1]. These metabolism-induced changes in local vasomotor tone are complimented by local and global sympathetic tone changes mediated through α-adrenergic receptor stimulation and systemic catecholamine release [2]. …