Phasic Variations in Peripheral Coronary Resistance and Their Determinants

Information regarding the successive changes of resistance in the coronary branches and their determinantIs is of paramount importance both in understanding the phasic changes of coronary flow and in interpreting the actions of drugs upon the intact coronary circulation. It seemed that a study of the pressure pulse from the peripheral end of a coronary vessel (peripheral coronary pressureP.C.P.) should supply this information. This report deals with a description of such pulses recorded by a calibrated optical manometer together with an analysis of their phasic variations and of their reliability in appraising the variations of peripheral coronary resistance under natural conditions. PROCEDURE. In a first series of experiments aortic and peripheral coronary pressures were simultaneously recorded by two optical manometers (Wiggers pattern). The cannula of the coronary manometermodified as illustrated in figure lA-was inserted into the peripheral end of the ligated descending ramus as indicated in figure lA, the precautions emphasized by Wiggers and Cotton (1933) being observed. Through the lateral connection and stopcock (a> the peripheral coronary vessel was perfused with Locke’s solution, except when records were being taken. Experience had taught us that by this expedient coagulation in the cannula tip could be prevented and the danger of the heart failing through fibrillation or hypodynamic action could generally be averted. During the course of such studies the discovery was made by Tennant and Wiggers (1935) that an area so perfused extends during systole instead of shortening. Since replacement of a normal systolic shortening by an extension might conceivably alter the peripheral coronary resistance changes, a second metlhod for recording P.C.P. was devised by which normal contractions were retained in the area studied. The procedure consisted in isolating the anterior descendens or the circumflex ramus and also a suitable side branch and in tying the coronary cannula into the