Validation and utility of novel volume reduction technique for determination of parallel conductance

The parallel conductance volume, created by the conductivity of structures surrounding the ventricular blood pool, can be estimated by using a saline dilution technique. This paper examines the use of a novel volume reduction method, during a standard vena caval preload reduction maneuver, as an alternative to the routinely used saline dilution method to calibrate conductance catheter measurements in the left (LV) and right ventricle (RV) of animals and humans. The serial reproducibility of both methods was examined by measurement of percent difference, and by assessing the coefficient of repeatability 1) between two measurements within the same subject, 2) between the two techniques, and 3) interobserver variability. The effect of ventricular size and contractile state on the volume reduction technique was also observed. It was essential to ensure the technique was not affected by inotropic state. The volume reduction technique and saline dilution method were repeated at three different loading states (baseline, 5, and 10 microg x kg(-1) x min(-1) of dobutamine). The coefficient of repeatability between serial measurements was similar for both the volume reduction and saline dilution methods, and good interobserver variability was demonstrated. The volume reduction technique was compared with the saline dilution technique over a large range of ventricular sizes. No significant difference was observed in the RV or LV of adult humans or in the LV of neonatal pigs and children. There was no significant effect on either the saline dilution or the volume reduction technique as the inotropic state increased. In conclusion, the volume reduction technique is neither affected by ventricular size nor contractile state, is repeatable between different observers, and can be used to substitute the saline dilution method when preload reduction of the ventricle is being employed.