[Noninvasive measurement of cardiac output by pulsed Doppler echocardiography. Correlation with thermodilution]

Cardiac output was measured simultaneously by pulsed Doppler echocardiography and thermodilution in 22 patients, 18 of whom also underwent atrial pacing at different rates to give a total of 42 different measurements. The aortic diameter was measured firstly at the aortic ring at the level of insertion of the aortic cusps and then at the point of maximum separation of the valve cups in the left parasternal long-axis view. The aortic velocities were recorded in the apical 5-chamber view immediately below the level of the aortic valve. The correlations obtained at the aortic ring (R1) and at the point of maximum separation of the valve cusps (R2) were 0.77 (y = 0.67x + 1.17: standard error = 0.81 l/m) and 0.64 (y = 0.56x + 0.87; standard error = 1.01 l/mn) respectively. The correlations were much better when 7 technically unsatisfactory measurements were excluded (R2 = 0.76: y = 0.59x + 0.74: standard error = 0.79 l/mn) (R1 = 0.87: y = 0.72x + 1.04: standard error = 0.65 l/mn). THe correlations of stroke volume measured at aortic ring level also improved from r = 0.82 (y = 0.75x + 7.29: standard error = 8.9 ml) to r = 0.89 (y = 0.78x + 7.38: standard error = 7.3 ml). The measurement of cardiac output by pulsed Doppler echocardiography in the aortic root seems to be reliable. The correlations of the values of stroke volume and cardiac output with the thermodilution method are good, allowing detection of beat-to-beat variations of cardiac output, in suitable patients in the hands of experienced operators.