Left ventricular mural force changes as reflections of induced alterations in myocardial pump performance

Strain gauge measurements of changes in left ventricular mural force seen during the ejection phase of the cardiac cycle were examined for a relation to ventricular emptying efficiency. Left ventricular pressure and mural force were recorded at aortic valve opening and closing, then residual fractions were calculated using (a) a representative radius determined from the LaPlace formula (MF = pi PR2), (b) mural force recordings alone, and (c) intraventricular pressure recordings alone. These fractions were compared to other residual fractions simultaneously obtained by thermodilution. Comparisons were made during changes in blood pressure, heart rate, and cardiac contractility. Findings were: 1. Significant correlation is seen when residual fractions, calculated from mural force alone or representative radii (mural force and left ventricular pressure) are regresed against the residual fraction obtained by thermodilution. 2. No relation is seen when residual fraction, calculated from intraventricular pressure, is similarly regressed against the residual fraction obtained by thermodilution. 3. It follows that mural force changes occurring during ventricular ejection do reflect ventricular dimension changes during this period. Moreover, directly recorded mural force can be used to calculate representative ventricular radii which more accurately reflect ventricular size changes. On the other hand, intraventricular pressure, which does not necessarily determine ventricular size, does not reflect ventricular emptying efficiency.