The conductance volume catheter technique for measurement of left ventricular volume in young piglets

The conductance catheter has been used extensively in the adult for instantaneous and continuous measurement of left ventricular volumes, but has not been validated for use in the small heart. To determine the accuracy of this technique, we simultaneously measured left ventricular volume by the conductance catheter and biplane cineangiography in nine piglets (2-5 wk of age) over a wide range of volumes experimentally altered by volume infusion, hemorrhage, inferior vena caval occlusion, or administration of phenylephrine, isoproterenol, or propranolol. We performed 110 comparisons and determined parallel conductance of contiguous structures (alpha Vc) for each comparison using the saline technique. End-systole and end-diastole volumes were estimated by angiography using Simpson's rule. Raw and alpha Vc-corrected conductance volumes were compared to simultaneously obtained angiographic volumes by multiple regression analyses, using dummy variable coding for the effects of the interanimal variability and the phase of the cardiac cycle. Raw conductance volumes correlated highly with the cineangiographic volumes (r = 0.97), and the coefficient of angiographic volumes was near identity (1.11 +/- 0.04). The phase of the cardiac cycle did not have a significant effect. However, alpha Vc-corrected conductance volumes correlated less (well (r = 0.85), probably related to the fact that estimated alpha Vc was found to vary with ventricular volume. Thus, the conductance catheter affords a very accurate technique for measuring instantaneous changes in ventricular volume in the small heart, although correction to absolute volumes using the saline technique for estimation of alpha Vc may induce some inaccuracy.