Hemodynamic effects of controlled degrees of coronary artery stenosis in short-term and long-term studies in dogs.

Coronary and aortic blood flow, aortic and distal coronary blood pressure were measured with electromagnetic flowmeters and pressure gauges in 15 anesthetized dogs with the chest left open. Increasing degrees of known, fixed, partial coronary artery obstruction were applied with concentric plastic cylinders 3 mm. in length and with varying internal diameters. Because these plastic cylinders are radiolucent and can also be permanently implanted, postoperative arteriograms were taken to evaluate the degree of stenosis produced. At necropsy the degree of obstruction was checked by ligating and removing the narrowed vessel and examining a histologic section of a stenosed portion. The reactive hyperemic response to a 20 second complete occlusion was recorded with amounts of obstruction varying from 10 to 90 per cent. The reactive hyperemia began to decrease with an average of 36 +/- 10 per cent stenosis. A pressure gradient of 10 mm. Hg across the obstruction occurred with an average of 57 +/- 8 per cent stenosis. The reactive hyperemic response was abolished with an average of 75 +/- 6 per cent stenosis, and with greater degrees of stenosis the total flow began to decrease below control levels. The phasic coronary flow pattern was also altered with increasing amounts of fixed partial obstruction. As the per cent of stenosis was increased, the ratio of diastolic to systolic coronary flow decreased. When reactive hyperemia was abolished, very little diastolic-to-systolic variation remained.