THE INFLUENCE OF ALTERATIONS IN THE CARDIAC LOADING CONDITIONS ON INDICES OF MYOCARDIAL CONTRACTILITY IN THE ANAESTHETIZED DOG

Abstract

1. An online analogue computer was used to measure myocardial contractility as the ratio dP/dt/IIT where dP/dt is maximum rate of change of left ventricular pressure and IIT is integrated isometric tension. 2. In the open thorax anaesthetized dog, max (dP/dt) and dP/dt/IIT were compared during alterations in preload, by partial vena caval occlusion, and changes in after‐load obtained by acetylcholine injections and by partial occlusion of the descending thoracic aorta. 3. A fall in preload lowered max (dP/dt) but did not alter dP/dt/IIT A rise and fall in afterload produced respectively an increase and decrease in max (dP/dt) but dp/dt/IIT was unaltered. 4. From expanded time base recordings..