Why the study?
What is the effect of heart rate and intracoronary isoproterenol, levarterenol, and epinephrine on coronary flow and resistance?
What is the effect of heart rate and intracoronary isoproterenol, levarterenol, and epinephrine on coronary flow and resistance?
Intracoronary isoproterenol, levarterenol, and epinephrine decrease total coronary resistance primarily through intravascular effects, with negligible impact on extravascular resistance.
Animal data suggest intravascular dominance in coronary resistance reduction; hypothesis-generating for human coronary flow studies.
The effect was determined of changes in heart rate and of intracoronary isoproterenol, levarterenol, and epinephrine on coronary flow in the stopped and beating heart. It was possible by this means to estimate the relative action of these variables on the extravascular and intravascular resistance of the coronary bed in a heart perfused at constant pressure. As heart rate was increased extravascular resistance rose, but intravascular resistance fell to a greater extent indicating a fall in net coronary resistance. Isoproterenol had the greatest and epinephrine the least effect in decreasing the total coronary resistance. The three drugs tested caused only a small fall in extravascular resistance. Since the effect was small, it was concluded that extravascular resistance can be ignored in determining the direct effect of these drugs upon the coronary vasculature.
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Lewis et al. (1961) studied this question.
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