Background: We assessed the relation between the severity of stenosis in a coronary artery and the degree of impairment of myocardial blood flow. Studies in laboratory animals have shown that as the degree of coronary-artery stenosis increases, the maximal coronary flow measured after maximal vasodilation progressively decreases, with a concomitant decrease in basal flow. However, this relation has not been carefully documented in humans through measurement of myocardial blood flow.
Methods: We studied 35 patients with single-vessel coronary artery disease and normal left ventricular function and 21 age-matched controls. Regional myocardial blood flow in the area supplied by the stenosed artery was measured by positron-emission tomography with oxygen-15-labeled water while the subject was at rest (basal flow) and during hyperemia induced by the intravenous administration of the vasodilator adenosine (140 micrograms per kilogram of body weight per minute) or dipyridamole (0.56 mg per kilogram).
Results: The mean (+/- SD) basal myocardial blood flow was 1.14 +/- 0.42 ml per minute per gram of tissue in the patients and 1.13 +/- 0.26 ml per minute per gram in the controls; during hyperemia, myocardial flow was 2.10 +/- 1.16 and 3.37 +/- 1.25 ml per minute per gram (P < 0.001), respectively. Basal flow was unchanged regardless of the severity of stenosis, expressed as a percentage of the diameter of the affected vessel (range of degrees of stenosis, 17 to 87 percent). In contrast, flow during hyperemia correlated inversely and significantly with the degree of stenosis and correlated directly with the minimal luminal diameter. The coronary vasodilator reserve (defined as the ratio of flow during hyperemia to flow at base line) began to decline when the degree of stenosis was about 40 percent and approached unity when stenosis was 80 percent or greater.
Conclusions: In humans, basal myocardial blood flow remains constant regardless of the severity of coronary-artery stenosis. However, during hyperemia, flow progressively decreases when the degree of stenosis is about 40 percent or more and does not differ significantly from basal flow when stenosis is 80 percent or greater.