Effect of stenosis on exercise-induced dilation of large coronary arteries.

The effects of a flow-limiting stenosis on external circumflex coronary arterial diameter during treadmill exercise were studied in 10 instrumented dogs. Coronary arterial diameter was measured by sonomicrometry proximal to the stenosis-producing hydraulic occluder so that the effects of a post-stenotic pressure drop were excluded. With no stenosis, heart rate increased (116 +/- 7 to 183 +/- 10 beats/min, p less than 0.001), aortic pressure increased (97 +/- 3 to 105 +/- 5 mm Hg. p less than 0.005), circumflex coronary blood flow increased (48 +/- 8 to 72 +/- 8 ml/min, p less than 0.001), and circumflex coronary diameter increased (3.82 +/- 0.29 to 3.93 +/- 0.27 mm, p less than 0.01). In the presence of a flow-limiting stenosis, heart rate increased (120 +/- 6 to 176 +/- 9 beats/min, p less than 0.001), aortic pressure did not change significantly (95 +/- 4 to 92 +/- 4 mm Hg), circumflex coronary blood flow increased slightly (39 +/- 8 to 46 +/- 9 ml/min, p less than 0.005), and circumflex coronary arterial diameter did not change significantly (3.78 +/- 0.29 to 3.80 +/- 0.28 mm). The stenosis prevented the increase in aortic pressure, blunted the increase in circumflex coronary blood flow (24 +/- 4 versus 7 +/- 2 ml/min, p less than 0.005), and prevented the increase in circumflex coronary arterial diameter. Therefore normal coronary arteries dilated during exercise and a flow-limiting stenosis prevented exercise-induced coronary dilation proximal to the stenosis, possibly due to both the failure of aortic pressure to increase and less flow-induced endothelium-dependent dilation.