PRECAPILLARY SERVO CONTROL OF BLOOD-PRESSURE AND POSTCAPILLARY ADJUSTMENT OF FLOW TO TISSUE METABOLIC STATUS - A NEW PARADIGM FOR LOCAL PERFUSION REGULATION

Background There are several shortcomings in current understanding of how the microvasculature maintains tissue homeostasis. Presently unres olved issues include (1) integration of the potentially conflicting ne eds for capillary perfusion and hydrostatic pressure regulation, (2) a n understanding of signal transmission pathways for conveying informat ion about tissue energetic status from undersupplied tissue sites to t he arterioles, (3) accounting for the experimentally observed interrel ations between precapillary and postcapillary resistances, and (4) an explanation of how precise local adjustment of perfusion to metabolic demands is achieved. Methods and Results A novel conceptualization of how local microvascular control mechanisms are coordinated is proposed , according to which blood flow is adjusted to the metabolic needs of the tissue by the venules. Arteriolar action is merely called on for c ontrolling capillary pressure through myogenic response and shear stre ss-induced vasodilation. A mathematical model of this theory is introd uced and evaluated using well-established experimental data from the l iterature on regulating mechanisms of microvessel diameters exclusivel y. The model results demonstrate the suggested mode of microvascular o peration to be functional and efficient under conditions present in vi vo. Moreover, the predicted vascular responses are large enough to cov er the entire range observed in exercising skeletal muscle during adju stment of perfusion to higher performance levels. Conclusions Precapil lary pressure regulation combined with postcapillary adjustment of per fusion to tissue metabolic status is suitable to resolve the above sho rtcomings in our current understanding of microvascular control. With mathematical modeling based on experimental data, this mode of microva scular operation is shown to be functional and effective in controllin g muscle microcirculation.