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 required for these measurements, their utilization
for serial evaluations in cardiac patients is not practical. A noninvasive technique
to measure contractility utilizing radionuclide ventriculography would,
therefore, be useful. End-ejection elastance was calculated in 10 normal subjects
from simultaneous cuff blood pressure, carotid pulse waveform and
radionuclide ventriculogram measurements at baseline and during dobutamine
infusion. End ejection pressure was measured by linear interpolation of the
carotid pulse waveform. End ejection volume was calculated from end diastolic
volume and ejection fraction. Loading conditions were altered with nitroprusside
and phenylephrine and elastance was estimated as the slope of the
end ejection pressure-volume relationship for each inotropic state using linear
regression. Under control conditions, end ejection elastance could be determined
with this noninvasive technique in all the normal subjects and was 1.49
± 0.27 mm Hg/ml. During dobutamine infusion end ejection elastance was
3.14 ± 1.45 in the 7 subjects in whom it could be measured (p = 0.003). In the
7 subjects with paired data end-ejection elastance increased from 1.42 ± 0.19
to3.14 ± 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 regression analysis from
which elastance was estimated was >0.87 in 12 of these 15 determinations.
End-ejection elastance measured noninvasively utilizing only radionuclide
ventriculography and carotid wave pulse tracings can serve as an index of left
ventricular contractility.