Left Ventricular Pressure -Volume Relationships and Myocardial Oxygen Consumption in the Isolated Heart

An isolated dog-heart preparation, in which absolute volumes were known, was employed to determine left ventricular pressure-volume relationships and myocardial oxygen consumption. Loading was varied from the extreme of zero pressure change to zero volume change during systole. Maximum peak systolic pressures were developed by isovolumetric, and maximum stroke volumes by isobaric contractions. When the load was varied to allow both pressure and volume to change in systole, the peak systolic pressures and the simultaneously determined ventricular volumes could be plotted as a "peak systolic pressure-volume line." Moderate changes in diastolic volume had little effect on the position of the line, and the mechanical work of the heart appeared to depend on the nature of the load rather than the diastolic volume. Epinephrine and digitalis glycosides did not affect diastolic pressure-volume relationships. Heart rate affected the diastolic pressure-volume curve only at rapid rates, where changes in the rate of relaxation produced apparent differences in compliance. Myocardial oxygen consumption is shown to be correlated with peak systolic pressure or volume, and is not mainly determined by either diastolic volume or stroke work.