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 alt ernative to the routinely used saline dilution method to calibrate conducta nce catheter measurements in the left (LV) and right ventricle (RV) of anim als and humans. The serial reproducibility of both methods was examined by measurement of percent difference, and by assessing the coefficient of repe atability 1) between two measurements within the same subject, 2) between t he two techniques, and 3) interobserver variability. The effect of ventricu lar size and contractile state on the volume reduction technique was also o bserved. It was essential to ensure the technique was not affected by inotr opic state. The volume reduction technique and saline dilution method were repeated at three different loading states (baseline, 5, and 10 mug.kg(-1). min(-1) of dobutamine). The coefficient of repeatability between serial mea surements was similar for both the volume reduction and saline dilution met hods, and good interobserver variability was demonstrated. The volume reduc tion 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 reduc tion 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 subst itute the saline dilution method when preload reduction of the ventricle is being employed.