[The determinants of intramyocardial pressure (author's transl)]

In 20 open-chest dogs intramyocardial pressure was measured simultaneously in two regions: a) in the normal myocardium (IMPsp) b) in a controlled perfused area of the myocardium, supplied by a cannulated coronary artery (IMPp). The preparation permitted the study of the influence of contractility, ventricular pressure and coronary blood flow on IMP. 1. A 47% change in coronary flow with a 26% change in coronary perfusion pressure results in changes of systolic and diastolic IMPp of 14% and 29% respectively. These effects can be explained by variations of intramural fluid content and, hence, of diastolic fiber length. 2. Changes of systolic ventricular pressure (mean 27%) by preload variations result in a mean change of systolic IMPsp of 19% and of systolic IMPp of 11%. 3. Changes of systolic ventricular pressure (mean 33%) by afterload variations augment IMPsp by 30% and IMPp by 13%. 4. The increases of IMPsp and IMPp induced by instantaneous changes of afterload are equal. The most important determinants of IMP are myocardial contractility, coronary perfusion and intraventricular pressure. The influence of coronary perfusion and ventricular pressure on IMP is of the same order of magnitude.