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The effect of norepinephrine infusion on the coronary circulation has been studied in 21 subjects. In doses ranging from 2 to 17 µg. base per minute norepinephrine caused a pari passu rise in perfusing pressure and coronary flow of 16 per cent above the control state. Despite an increase in cardiac oxygen consumption, coronary vascular resistance was unchanged, suggesting no vasodilatation in the coronary bed. On the contrary, oxygen extraction across the heart increased, implying that oxygen needs were inadequately met by rise in flow. An increase in vascular tone induced by norepinephrine is inferred from the unchanged coronary resistance at a higher perfusion pressure. Responses of the normal and failing left ventricle groups were qualitatively the same as for the group as a whole. The failure group showed greater tendency to meet oxygen needs by increased extraction than did the normal hearts. Although these observations are not strictly applicable to the role and effects of norepinephrine in states of clinical shock, nonetheless it seems likely that norepinephrine induces a suboptimal rise in coronary flow that may set the stage for ultimate myocardial ischemia, particularly when coronary perfusion pressure is inadequate.
Yurchak et al. (Sat,) studied this question.