Measuring left ventricular dimensions by conductance catheter in the rabbit.

A miniaturized (3.5 F), six-electrode conductance catheter was tested in 18 anaesthetized adult rabbits (weight 3.8-4.6 kg, ethylurethane 2.5 g kg-1). In eight animals, the reference stroke volume (ref-SV) was obtained by an electromagnetic flow probe, while reference end-diastolic volume (ref-LVEDV) was computed by dividing ref-SV by undamped thermal dilution ejection fraction (ref-EF) estimates. Comparisons with conductance indexes (z-SV, z-LVEDV and z-EF) were made at baseline, subsequent levels of graded haemorrhage and reinfusion state. In 10 animals intraventricular segmental conductance was compared with echocardiographic left ventricular cross-section (5 MHz short-focus probe), in the basal state and during acute left ventricular volume changes generated by inferior vena cava balloon occlusion. In each experiment, parallel conductance due to the tissues surrounding the left ventricle (Gp) was determined by infusing a 5M NaCl solution bolus into the right ventricle. Linear regression analysis showed fairly good correlations between z-SV, z-LVEDV and z-EF and reference indexes (r = 0.84, r = 0.83, and r = 0.72, respectively; P less than 0.001 in all cases). A linear regression analysis from 17 interventions (inferior vena cava balloon occlusion) showed a good correlation between left ventricular echocardiographic cross-sectional area and conductance, and higher correlation coefficients, r ranging from 0.870 to 0.986 were obtained from continuously sampled conductance and echographic measurements. Parallel conductance Gp was correlated (r = 0.807, P less than 0.01) with the intercept of the regression line of echographic vs conductance data. The determination of Gp thus improved the accuracy of the left ventricular dimension estimate. These results add further evidence for the possibility of continuous monitoring of left ventricular dimension by means of a conductance catheter, and demonstrate the feasibility of such studies on small experimental animals.