Ventriculo-arterial coupling was estimated using a micromanometer catheter to obtain left ventricular pressure and a conductance catheter to obtain left ventricular volume. These invasive ...measurements were compared with ventriculo-arterial coupling obtained using echocardiography and mean femoral arterial pressure in 10 dogs. End-systolic elastance (Ees) was derived changing preload by caudal vena cava occlusion and by pharmacologically changing afterload. Two-dimensionally derived echocardiographic left ventricular volumes correlated better and showed narrower limits of agreement with volume measured using the conductance catheter than M-mode derived volumes. The best correlation and limits of agreement were obtained using the modified Simpson's formula and the cylinder-truncated cone-cone model. Excellent correlation was found between cardiac output obtained using the conductance catheter, thermodilution, and Doppler echocardiography. The range of limits of agreement however were approximately 1.2 L/min. Very good correlation was obtained between Ees and effective arterial elastance (Ea) obtained with and without cardiac catheterization. The limits of agreement, however, were less than ideal. Directional changes in Ees and Ea obtained without cardiac catheterization were correctly identified in all dogs after milrinone administration. The Ea obtained using the of ratio end-systolic pressure to stroke volume was a good estimation of the Ea obtained using a mathematical relation based upon the three-element Windkessel model of the vasculature. Effective arterial elastance, however, substantially underestimated the Ea obtained using the three-element Windkessel. The Ees to Ea ratio, stroke work, stroke work maximum and left ventricular mechanical optimality obtained with cardiac catheterization showed very good correlation with the same indexes obtained without cardiac catheterization. The limits of agreement, however, were too wide to allow adequate estimation of these indexes non-invasively. Milrinone increased cardiac output, mean and peak flow, and decreased time from end-diastole to the maximum acceleration of blood in the ascending aorta. Milrinone increased inotropy increasing Ees and pre-load recruitable stroke work. Ventriculo-arterial coupling was improved due to an increase in Ees and a decrease in Ea after milrinone administration. Milrinone decreased left ventricular afterload by decreasing peripheral resistance and increasing total arterial compliance with no effect on aortic characteristic impedance.
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