Medicine of the Future in America

Myocardial Oxygen Supply and Demand (4)

Adenosine is the byproduct of utilization of ATP which stores high energy’ phosphate (Fig 1). Myocardial metabolism releases adenosine which, under steady states, is constantly cleared by blood flow. With increased metabolic rates or decreased blood flow, adenosine accumulates, induces vasodilation, causes an increase in blood flow, and the steady-state concentration of adenosine is restored. The role of molecular oxygen as a mediator for metabolic control has also been studied extensively. Diminished molecular oxygen tension has a directly vasodilatory effect on smooth muscle cells and on the tone of precapillary sphincters of vascular beds. It is important to emphasize that variation of blood flow is not only mediated via changes in the caliber of presently open capillaries, but also through recruitment of closed microvascular beds. Although adenosine was used as the exemplifying mediator, it seems likely that metabolic control of coronary blood flow is mediated via multiple agents and there may be a cascade of messengers involved in this coupling reaction. buy flovent inhaler
Autoregulation: As is true in the central nervous system, blood flow in coronary arteries remains constant over a wide range of perfusion pressures (60-160 mm Hg). In other words, as the driving pressure changes, coronary resistance also changes in the reciprocal manner to keep blood flow constant. Coronary autoregulation was first described by Mosher et al.


Figure 1. Role of adenosine as a metabolic mediator of coronary blood flow.

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