Hypertonic saline method accurately determines parallel conductance for dual-field conductance catheter

Conversion of conductance catheter data to absolute ventricular volumes requires assessment of parallel conductance (G(P)). We determined the accuracy of G(P) obtained by the hypertonic saline method (G(saline)(P)) compared with angiographically derived G(P) (G(Angio)(P)) and quantified the variabilities of G(P) for the dual-field conductance catheter method in nine anesthetized sheep studied at baseline, treated with dobutamine, and subjected to volume loading and beta -blockade. G(saline)(P) and G(Angio)(P) showed an excellent linear correlation (G(saline)(P) = 1.002.G(Angio)(P) + 0.001 Omega (-1), R-2 = 0.92), and Bland-Altman analysis yielded a nonsignificant bias and narrow limits of agreement (bias +/- 2SD = 0.002 +/- 0.112 Omega (-1)). Within-animal variability of G(P) was very similar with both methods and was due to changes in blood conductivity rather than geometrical changes. Variability between animals was significant (26.3% of mean for G(saline)(P) and 25.7% for G(Angio)(P)) and thus warrants individual assessment. Variations during the cardiac cycle were not significantly different from zero. With biplane angiography used as gold standard, the hypertonic saline method accurately determines G(P) for the dual-field conductance catheter over a wide range of hemodynamic conditions.