END EJECTION ELASTANCE DETERMINED FROM RADIONUCLIDE VENTRICULOGRAPHY AND CAROTID PULSE RECORDS AS AN INDEX OF LEFT-VENTRICULAR CONTRACTILITY

The objective of this study was to assess the ability of a noninvasive radionuclide method to measure left ventricular systolic elastance as an index of left ventricular contractility in normal individuals. End systolic and peak systolic elastance are considered load-independent indices of contractility. Since invasive procedures are usually requir ed for these measurements, their utilization for serial evaluations in cardiac patients is not practical. A noninvasive technique to measure contractility utilizing radionuclide ventriculography would, therefor e, be useful. End-ejection elastance was calculated in 10 normal subje cts from simultaneous cuff blood pressure, carotid pulse waveform and radionuclide ventriculogram measurements at baseline and during dobuta mine infusion. End ejection pressure was measured by linear interpolat ion of the carotid pulse waveform. End ejection volume was calculated from end diastolic volume and ejection fraction. Loading conditions we re altered with nitroprusside and phenylephrine and elastance was esti mated as the slope of the end ejection pressure-volume relationship fo r each inotropic state using linear regression. Under control conditio ns, end ejection elastance could be determined with this noninvasive t echnique in all the normal subjects and was 1.49 +/- 0.27 mm Hg/ml. Du ring dobutamine infusion end ejection elastance was 3.14 +/- 1.45 in t he 7 subjects in whom it could be measured (p = 0.003). In the 7 subje cts with paired data end-ejection elastance increased from 1.42 +/- 0. 19 to 3.14 +/- 1.45 (p = 0.022) during dobutamine infusion. Of the 17 end ejection elastance determinations, 15 were estimated from three or more loading conditions. The correlation coefficient of the linear re gression analysis from which elastance was estimated was greater than or equal to 0.87 in 12 of these 15 determinations. End-ejection elasta nce measured noninvasively utilizing only radionuclide ventriculograph y and carotid wave pulse tracings can serve as an index of left ventri cular contractility.