FIGURE 1.

Arteriolar dysfunction can produce ischemia in the absence of a flow-limiting stenosis

Top left: at rest, arterioles display a high level of resting tone, which determines the basal blood flow through the upstream arteries. Bottom left: during times of increased oxygen demand, CM release vasoactive metabolites (1), which leads to a drop in arteriolar resistance (2). The decreased arteriolar resistance elicits increased flow in upstream arteries (3), causing increased NO release and oxygen delivery to downstream capillaries (4), as well as FMD in the artery (5), further increasing flow. Top right: in the presence of a diffuse but non-flow-limiting stenosis, arterial resistance and coronary flow are not affected. Bottom right: when arteriolar dysfunction is present, CM release vasoactive metabolites (1) but arterioles do not respond with appropriate vasodilation (2), and arteriolar resistance remains high. In the absence of a drop in arteriolar resistance, the necessary increase in flow is attenuated (3), FMD does not occur (4), and ischemia results from the mismatch between metabolic demand and flow. R, resistance; FMD, flow-mediated dilation; NO, nitric oxide; CM, cardiomyocytes.