CORONARY MICROCIRCULATION - AUTOREGULATION AND METABOLIC CONTROL

The majority of studies examining the regulation of coronary blood flo w and vascular resistance have considered the coronary circulation as being composed of large conduit vessels and resistance vessels. Recent ly, it has become apparent that regulation of coronary microvascular r esistance is not distributed uniformly, but varies across different se gments or microdomains of the vasculature. Generally, small arterioles , those less than 100 mu m in diameter, respond differently than large r arterioles and small arteries. There are major differences in the le vel of autoregulatory control, myogenic control, endothelial modulatio n and control by metabolic factors across these various microvascular domains. There are also transmural variations which may account for so me of the differences in coronary blood observed between epicardial an d endocardial regions. In addition, interactions between these various regulatory mechanisms further complicate the understanding of coronar y microvascular regulation. Importantly however, it may be these compl ex interactions and heterogeneous regulatory mechanisms which allow fo r adequate perfusion of the myocardium under an extreme range of metab olic conditions. This segmental distribution of regulation suggests an integrative hypothesis of regulation whereby a variety of mechanisms play a role in the overall response.