Functional characteristics of the coronary microcirculation

For over 50 years, it has been recognized that coronary blood flow is preci sely matched to cardiac metabolism. The interactions which govern this matc hing remain unknown. In the current review, 3 specific aspects of coronary now regulation will be discussed: Specialization of function in different m icrovascular domains, influence of cardiac region on microvascular function and the interactions of vasoactive agents in control of coronary blood flo w Each level of the coronary microcirculation is affected by different physic al and chemical forces within the heart. These forces place special demands on these vessels and are in turn met by specialized vasodilator responses, including metabolic and flow-mediated vasodilation. Perfusion of the heart is also profoundly affected by the region perfused. The endocardium is aff ected by forces, notably cardiac contraction, in a different manner than th e epicardium. Thus, the microcirculation has specialized to meet these dema nds. Finally the factors determining microvascular tone appear to be coordi nated such that the loss of any individual dilator, such as nitric oxide, c an be compensated for by the increased contribution of another, such as ade nosine. This interplay may serve to protect the heart from ischemia during the early phases of coronary vascular disease when individual dilators may be impaired.