[Regional myocardial perfusion in coronary stenosis of varying degrees]

Stenoses of the left anterior descending coronary artery of varying severity (15-73% of internal diameter, 20-95% of internal surface) were created in 25 open-chest pigs. The regional distribution of myocardial blood flow perfusion was studied by the radioactive microspheres technique at rest and during reactive hyperemia. Reactive hyperemic responses to 10 sec occlusions were used to produce maximal flow increases and to judge the physiological significance of the narrowings in the subendocardial and subepicardial layers in calculating coronary flow reserves. Measurements of coronary reserve are sensitive indices of functional impairment even when resting flow is unimpaired. At 75% stenosis the subendocardial coronary reserve is completely abolished and the zone perfused by the stenosed artery is unable to increase its flow when needed if the experimental conditions do not change. Any further increase in oxygen demand will provoke electrical and metabolic disorders. For abolition of the subepicardial coronary reserve a 94% stenosis is required.