Radionuclide absolute left ventricular volumes during upright exercise: validation in normal subjects by simultaneous hemodynamic measurements

Abstract

A nongeometric radionuclide technique for the determination of absolute left ventricular volumes was validated during exercise in nine normal subjects. Simultaneous reference stroke volume and cardiac output measurements were obtained by the Fick method. The reference left ventricular volumes were calculated by combining the Fick stroke volume and the isotopic ejection fraction. Data were collected at rest in the supine and upright positions and during 60° upright exercise, at three levels of increasing severity. At rest, from supine to upright position, the reference end-diastolic volume decreased significantly from 182±24 ml to 154±21 ml (mean±SD, P<0.005); during upright exercise of low intensity, end-diastolic volume increased to 176±24 ml (P<0.05); at maximal exercise, end-diastolic volume was not different from the resting value in upright position. The end-systolic volume gradually decreased at rest from 67±11 ml in the supine position to 54±8 ml in the upright position (P<0.05) and to 32±7 ml at maximal exercise (P<0.005). Compared with these reference data, the scintigraphic measurements were significantly lower on average by 23% for stroke volume, 21% for cardiac output, 22% for end-diastolic volume, and 23% for end-systolic volume. The overall changes in stroke volume (P<0.05) and end-systolic volume (P<0.001) occurring at rest and during exercise were correctly detected by the scintigraphic method but the smaller changes in end-diastolic volume (less than 15%) were not (P<0.15) because they were within the range of the precision of the technique. If subtle changes in left ventricular volume are to be quantitated, attempts should be made to reduce the random variability of the scintigraphic method.