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Regional blood flow and contractile function: are they matched in normal, ischemic and reperfused myocardium?

One central hypothesis of cardiovascular physiology has been a balance between myocardial blood flow and contractile function during natural conditions, i.e. supply and demand are matched. This hypothesis was derived from studies relating total coronary blood flow to global ventricular function. The present article examines the relationship between myocardial blood flow and function on a regional level. In normal myocardium, considerable heterogeneity of blood flow exists, indicating similar heterogeneity of metabolic demand and potentially also function. However, when the degree of metabolic coupling between flow and function is questioned, there is no evidence whether or not flow and function are matched on a regional level. One closely related hypothesis of cardiovascular pathology has been an imbalance or mismatch between supply and demand during ischemia. Because myocardial function rapidly declines during early ischemia, residual, regional myocardial blood flow and function may be once again matched on a lower level. Such low-level supply-demand balance may persist over prolonged periods of ischemia and permit the myocardium to remain viable, i.e. the myocardium can "hibernate." Analyzing myocardial blood flow and function on a regional level has generated new insight into strategies of adaptation to the adverse situation of reduced blood flow. Whereas in hibernating (ischemic) myocardium, regional myocardial blood flow and function are matched, flow and function appear to be unmatched in reperfused, dysfunctional, i.e. 'stunned' myocardium. "Stunned myocardium" appears once more as a result of a strategy of adaptation, as the preceding ischemia did not induce irreversible myocardial damage but preserved the ischemic myocardium viable, although functionally impaired.