Flow through the coronary circulation is not dependent on the difference between the arterial and venous pressures; rather, it is dependent on the difference between the arterial pressure and ventricular luminal pressure (Figure 1.10). Incomplete relaxation of the ventricle as following myocardial infarct, causes luminal pressure to remain high, impeding coronary flow. Because luminal (and tissue) pressure is high during systole, particularly in the left ventricle, coronary flow is low, whereas luminal (and tissue) pressure falls during diastole permitting coronary flow to occur.
Thus coronary flow, particularly in the left ventricle, is maximal when aortic pressure is minimal or near minimal. The situation is similar in contracting skeletal muscle.
This phenomenon is also present during the contraction of skeletal muscle.
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