RESUMO
BACKGROUND: Measurement of absolute ventricular volume with the conductance catheter technique has been documented extensively for the left ventricle (LV). More recently, the same technique has been applied in studies of right ventricular (RV) performance. In the present study we performed simultaneous measurements of LV and RV volumes. Conversion of measured conductances to absolute volumes requires the assessment of slope factor alpha (α) and parallel conductance correction volume (Vc) for both the RV and LV. We investigated the magnitude and variability of these calibration factors during a typical study period of four hours. METHODS: In five anaesthetised, ventilated newborn lambs, conductance catheters were introduced into the LV and RV and a thermodilution catheter was positioned in the pulmonary artery. Alphas and Vc's were determined by thermodilution and hypertonic saline dilution, respectively, at one hourly intervals. At the same time points, biventricular haemodynamic parameters were obtained. Results were analysed by multiple linear regression analysis. RESULTS: During the course of the experiments all haemodynamic parameters were stable. There were no significant changes in Vc or α for either ventricle. RV-Vc was systematically higher than LV-Vc: both as absolute values and as percentage of the uncalibrated conductance signal (79% for RV, and 49% for LV, respectively). This probably reflects the geometrical differences of the two ventricles. Right ventricular ejection fraction (RV-EF) was higher than left ventricular ejection fraction (LV-EF), and neither changed significantly during four hours. CONCLUSION: These results show that calibration factors α and Vc for the RV, as well as EF, show values that are consistent with the observed haemodynamic stability and in line with the LV factors. These results indicate that the conductance catheter method can be used satisfactorily for biventricular function assessment.
