Coronary pressure-flow relationship and exercise: Contributions of heart rate, contractility, and α1-adrenergic tone

D. J. Duncker, N. S. Van Zon, M. Crampton, S. Herrlinger, D. C. Homans, Robert J Bache

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Abstract

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 α1-adrenergic vasoconstriction. Treadmill exercise that increased heart rate from 118 ± 6 beats/min at rest to 213 ± 8 beats/min (P < 0.01) decreased maximum coronary blood flows by decreasing the slope of the linear part of the pressure-flow relationship for coronary pressures ≥ 30 mmHg (slope(P ≥ 30)) from 12.3 ± 0.9 to 10.9 ± 0.9 ml · min-1 · g-1 · mmHg-1 (P < 0.01) and increasing the measured coronary pressure at zero flow (P(zf,measured)) from 12.6 ± 1.2 to 23.3 ± 2.0 mmHg (P < 0.01). Atrial pacing at 200 beats/min caused an increase of P(zf,measured) from 15.0 ± 1.6 to 18.3 ± 2.1 mmHg (P < 0.05) with no change in slope(P ≥ 30). While pacing continued, infusion of dobutamine (20 μg · kg-1 · min-1 iv) increased contractility to levels similar to those during exercise but caused no significant change in coronary blood flow, as a decrease of the slope(P ≥ 30) was compensated for by a slight decrease in P(zf,measured). α1- Adrenergic blockade with intracoronary prazosin (10 μg/kg) did not prevent the exercise-induced increase of P(zf,measured) but abolished the decrease of the slope(P ≥ 30). When the increases in heart rate, contractility, and α1-adrenergic vasoconstriction were prevented, exercise still increased P(zf,measured) from 15.8 ± 2.1 to 21.8 ± 2.6 mmHg (P < 0.05) but had no effect on the slope(P ≥ 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, α1-adrenergic vasoconstriction, and left ventricular filling pressure, with a minimal contribution of contractility.

Original languageEnglish (US)
Pages (from-to)H795-H810
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume266
Issue number2 35-2
StatePublished - 1994

Keywords

  • adenosine
  • coronary arterial stenosis
  • coronary blood flow
  • extravascular forces
  • minimum coronary resistance
  • α-adrenergic vasoconstriction

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