Hemodynamics of multiple versus single 50 percent coronary arterial stenoses.

The purpose of this study was to compare coronary blood flow in the presence of multiple fixed coronary arterial stenoses with that in the presence of a single stenosis of equivalent length and diameter. The study was performed using an in vitro pulse duplicating system. The aortic root section consisted of an acrylic mold of the root of the aorta of a calf. The coronary system was designed to produce coronary flow with physiological magnitudes and phasic patterns. Aortic and left ventricular pressures as well as the reduction in pressure across the coronary test section containing the stenotic segments were measured with catheter-tip micromanometers. Coronary flow was measured with a cannulating electromagnetic flow transducer. The fluid viscosity was 0.04 poise. Studies were performed sequentially with one 2 mm long arterial segment with a stenosis of 50 percent of luminal diameter, two such stenotic segments and three such stenotic segments in series. A single 4 mm long, 50 percent diameter stenotic segment and a 6 mm long, 50 percent diameter stenotic segment were also studied. The heart rate was 71 beats/min, stroke volume 80 ml and aortic pressure 140/75 mm Hg. A single 2 mm long, 50 percent stenotic segment caused a 6 percent reduction of coronary flow; three such stenoses in series caused a 19 percent reduction of coronary flow. In contrast, a single 6 mm long, 50 percent diameter stenotic segment caused only an 8 percent reduction of coronary flow. The results suggest that in a maximally dilated coronary bed, a greater reduction of coronary flow would occur in the presence of multiple short stenoses than in the presence of a single stenosis of equivalent length and diameter.