Determination of stroke volume and cardiac output during exercise: comparison of two-dimensional and Doppler echocardiography, Fick oximetry, and thermodilution

Simultaneous estimates of cardiac output were made during graded upright maximal exercise in 10 male subjects by means of Doppler velocity spectrum of ascending aortic flow, apical two-dimensional echocardiograms, thermodilution, and Fick oximetry. In 15 subjects, aortic annular and root diameters were measured during similar exercise from parasternal two-dimensional echocardiograms. The linear correlation between Doppler, two-dimensional echocardiography, and the invasive estimates ranged from r = .78 to r = .92. Both echocardiographic techniques were able to predict changes in invasive flow estimates with reasonable accuracy. Two-dimensional echocardiographic flow estimates underestimated invasive values by about 60%. The accuracy of Doppler flow estimates varied with the method of estimating aortic cross-sectional area. Greatest accuracy was obtained with areas calculated from diameters measured at the aortic value anulus with the leading edge-to-leading edge method of measurement. Correlation coefficients comparing Doppler and thermodilution flow estimates were generally higher (r = .75 to .96, mean .86) for individuals than for the group, but accuracy of the Doppler estimates in single subjects was quite variable. Aortic diameters did not increase from rest to moderate levels of upright exercise. A 3% to 5% increase in resting aortic diameter was noted in the upright posture as compared with the supine. Doppler flow estimates were obtained in all subjects to maximal exertion but in only a minority of subjects with two-dimensional echocardiography or thermodilution. Thus two-dimensional and Doppler echocardiography offer a noninvasive means of estimating cardiac output during vigorous exercise. The Doppler technique is technically more suitable to the study of exercise than two-dimensional echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)