IN-VITRO AND FINITE-ELEMENT MODEL INVESTIGATION OF THE CONDUCTANCE TECHNIQUE FOR MEASUREMENT OF AORTIC SEGMENTAL VOLUME

This investigation examined the feasibility of applying the conductanc e catheter technique for measurement of absolute aortic segmental volu me. Aortic segment volume was estimated simultaneously in vitro by usi ng the conductance catheter technique and sonomicrometer crystals. Exp eriments were performed in five isolated canine aortas. Vessel diamete r and pressure were altered, as were the conductive properties of the surrounding medium. In addition, a three-dimensional finite-element mo del of the vessel and apparatus was developed to examine the electric field and parallel conductance volume under different experimental con ditions. The results indicated that in the absence of parallel conduct ance volume, the conductance catheter technique predicted absolute cha nges in segmental volumes and segmental pressure-volume relationships that agreed closely with those determined by sonomicrometry. The intro duction of parallel conductance volume added a significant offset erro r to measurements of volume made with the conductance catheter that we re nonlinearly related to the conductive properties of the surrounding medium. The finite-element model was able to predict measured resista nce and parallel conductance volume, which correlated strongly with th ose measured in vitro. The results imply that absolute segmental volum e and distensibility may be determined only if the parallel conductanc e volume is known. If the offset volume is not known precisely, the co nductance catheter technique may still be applied to measure absolute changes in aortic segmental volume and compliance.