Effects of coronary stenoses on coronary flow reserve and resistance

Abstract

Resting coronary flow and regional distribution are not affected by narrowing of up to 85 percent of arterial diameter and therefore provide little insight into the effects of stenoses on coronary hemodynamics. However, maximal coronary flow and coronary flow reserve are markedly reduced by constrictions that do not affect resting flow. Accordingly, coronary flow reserve and its relations to pressure-flow-resis-tance characteristics of 177 single (10 dogs) and 125 double coronary stenoses in series (7 dogs) were studied in open chest preparations. Coronary flow, aortic pressure and left circumflex coronary pressure distal to a single or to each of two separate adjustable coronary constrictors in series were simultaneously recorded while flow was varied from basal to maximum by intracoronary injections of contrast medium. The hyperemic response to contrast medium is a quantitative measure of coronary flow reserve which was closely related to, and predictive of, the following characteristics of single and double stenoses in series: (1) total pressure gradient and distal circumflex perfusion pressure at resting coronary flow; (2) total pressure gradient and distal circumflex pressure at hyperemic flow when effects of stenoses are greatest; and (3) coronary stenoses resistance. Thus, the hyperemic response after injection of contrast medium, or coronary flow reserve, is in itself a quantitative measure of the pressure-flow-resistance characteristics of coronary constrictions. In addition, resistances of coronary stenoses in series are shown to be additive; the flow effects of stenoses in series are not generally determined by the dominant or most severe lesion, contrary to common clinical precepts. These concepts are applicable to patients in assessing the effects of stenoses on coronary hemodynamics.