Reduced myocardial blood flow resulting from dynamic changes in coronary artery stenosis

To evaluate the interaction of coronary vasomotor tone and stenosis, we studied the effects of ergonovine and adenosine on partially obstructed coronary arteries in 6 closed chest dogs. Coronary stenosis was created by partially inflating a balloon catheter with a distal lumen in the left anterior descending or circumflex coronary artery. Stenotic resistance was calculated as the mean pressure gradient across the stenosis divided by the mean blood flow measured with 15 micron radioactive microspheres. Coronary artery vasoconstriction, induced by ergonovine (0.6 mg i.v.), caused a small, but nonsignificant, increase in stenotic resistance (1.42 +/- 0.25 to 2.68 +/- 0.64 mm Hg/ml per min) and had no effect on myocardial blood flow. Coronary arteriolar dilation induced by adenosine increased stenotic resistance (1.52 +/- 0.25 to 9.01 +/- 2.49 mm Hg/ml per min, P less than 0.05) and the pressure gradient across the stenosis (18.8 +/- 3.0 to 41.3 +/- 7.5 mm Hg, P less than 0.05). Adenosine increased myocardial blood flow from 0.52 +/- 0.05 ml/min per g to 1.43 +/- 0.20 ml/min per g (P less than 0.05) in the regions supplied by unstenosed arteries, while in the region perfused by the stenosed artery blood flow fell from 0.51 +/- 0.06 to 0.29 +/- 0.13 ml/min per g (P less than 0.05), with the endocardium most severely affected (0.55 +/- 0.04 ml/min per g to 0.26 +/- 0.09 ml/min per g, P less than 0.05). Thus changes in severity of stenosis produced by altered coronary pressure and flow can influence blood flow to the myocardium. Such dynamic changes in coronary artery stenosis may be important in the pathogenesis of angina and myocardial infarction.