[The effect of slight to moderate stenoses on the coronary reserve and hemodynamics]

The effect of slight to moderate stenosis (less than or equal to 50% of external diameter) on the coronary reserve and coronary hemodynamics has been studied in 8 pigs. The coronary reserve was measured by the technique of reactive hyperemia, which consists of brief total occlusion of the artery concerned and sudden relaxation. The decrease in coronary reserve is directly proportional to the degree of stenosis. At 73% of stenosis the coronary reserve is completely abolished and the zone perfused by the stenosed artery is unable to increase its flow when needed. Slight to moderate stenosis soon causes the appearance of pressure gradients through the stenosis. The gradient increases simultaneously and proportionately to the increase of flow and is directly proportional to the degree of stenosis. These gradients decrease the perfusion pressure, and this induces an unhomogeneous distribution of myocardiac perfusion.