Intramyocardial Pressure and Strength of Left Ventricular Contraction

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Abstract
Intramyocardial pressure was followed with the Johnson-DiPalma method in isolated hearts and in hearts in situ. Systolic intramyocardial pressure curves from hearts in situ exhibited two pressure peaks which were believed to coincide with peak contractile tension and with myocardial fiber shortening, respectively. The following factors influenced intramyocardial pressure: ventricular cavity volume, heart rate, coronary perfusion pressure, outflow resistance, and "epicardial" compression. The contractile strength of the left ventricle varied in proportion with the intramyocardial pressure; it did not appear to be regulated primarily by diastolic volume or by metabolic support. Intramyocardial pressure was believed to determine the contractile strength of the heart by controlling the release of a potentiating substance.