Coronary pressure-flow relationship and exercise: contributions of heart rate, contractility, and alpha 1-adrenergic tone

We examined the impeding effects of exercise on coronary blood flow by analyzing exercise-induced changes in the pressure-flow relationship during maximal coronary vasodilation with adenosine in chronically instrumented dogs and assessed the individual contributions produced by heart rate, contractility, and alpha 1-adrenergic vasoconstriction. Treadmill exercise that increased heart rate from 118 +/- 6 beats/min at rest to 213 +/- 8 beats/min (P or = 30 mmHg (slopeP > or = 30) from 12.3 +/- 0.9 to 10.9 +/- 0.9 ml.min-1 x g-1 x mmHg-1 (P or = 30. While pacing continued, infusion of dobutamine (20 micrograms.kg-1 x min-1 i.v.) increased contractility to levels similar to those during exercise but caused no significant change in coronary blood flow, as a decrease of the slopeP > or = 30 was compensated for by a slight decrease in P zf,measured. alpha 1-Adrenergic blockade with intracoronary prazosin (10 micrograms/kg) did not prevent the exercise-induced increase of P zf,measured but abolished the decrease of the slopeP > or = 30. When the increases in heart rate, contractility, and alpha 1-adrenergic vasoconstriction were prevented, exercise still increased P zf,measured from 15.8 +/- 2.1 to 21.8 +/- 2.6 mmHg (P or = 30. This residual increase in P zf,measured correlated with the concomitant increase in left ventricular filling pressure. In conclusion, exercise-induced decreases of maximum coronary blood flow were explained by increases in heart rate, alpha 1-adrenergic vasoconstriction, and left ventricular filling pressure, with a minimal contribution of contractility.