Relationships between left ventricular volume, ejected fraction, and wall stress

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Abstract
Relationships between left ventricular filling, end-systolic and end-diastolic volumes, ejected fraction, and left ventricular wall stress were studied under controlled hemodynamic conditions in a canine right-heart bypass preparation. Left ventricular volumes were measured by the thermodilution technic and left ventricular circumference was mea-suredbya mercury-in-rubber gauge. Left ventricular wall stress was calculated from left ventricular pressure and instantaneous internal volume, the latter derived from end-diastolic volume and relative circumference changes. Increased cardiac filling at constant peak left ventricular pressure and heart rate increased ejected fraction with a small increase in end-systolic volume relative to the increase in end-diastolic volume. Peak left ventricular stress also increased. When cardiac filling was increased at constant peak stress, end-systolic volume was constant. End-systolic volume varied directly with peak stress. These relationships appear to be an expression of cardiac muscle mechanics.