Ineffectiveness of Drugs upon Collateral Coronary Flow.

Abstract

Valid experimental evidence as to whether a drug can improve collateral coronary blood flow to an ischemic area is difficult to obtain. Observation of color changes or comparison of size of infarcts without and with use of a drug are subject to too many contingencies to have a certain value. Observations as to the effects of drugs upon coronary inflow and outflow do not test the response of collateral vessels and ignore the hemodynamic alterations resulting from occlusion of the main branch. We therefore studied the reliability of 4 other possible criteria of changes in collateral flow, viz., (1) changes in rate of blood flow from a peripheral coronary ramus; (2) alterations in mean peripheral coronary pressure; (3) changes in inflow rate at high perfusion pressures before and after use of drugs—the latter being administered during a period when the area was not perfused; and (4) the ability of drugs given by inhalation or intravenously to prevent contractile failure after ligating a ramus or of restoring such contractions in an ischemic area. The first and second of the methods cannot be used as criteria. The third method also proved to be no criterion of changes in collateral flow alone but is useful because the flow changes are a resultant of vascular and extravascular factors which modify resistance to flow. The following results were obtained: 1. Drugs of the theobromine and theophylline group have a very insignificant effect on collateral flow to an ischemic region. 2. The nitrite group cause a slight decrease in coronary resistance within the ischemic area but it appears more probable that this is due to attendant reductions of intraventricular tension rather than to effects of drugs reaching the vessels of an ischemic area. At any event this slightly beneficial action is more than offset by the fact that the driving pressure in larger collateral vessels in the left ventricle is reduced.