ACCURACY OF THE CONDUCTANCE CATHETER FOR MEASUREMENT OF VENTRICULAR VOLUMES SEEN CLINICALLY - EFFECTS OF ELECTRIC-FIELD HOMOGENEITY AND PARALLEL CONDUCTANCE

The conductance-volume method is an important clinical tool which allo ws the assessment of left ventricular function in vivo, However, the a ccuracy of this method is limited bg the homogeneity of electric field the conductance catheter produces and the parallel conductance of sur rounding structures, This paper examines these sources of error in, vo lumes seen clinically, The characteristics of electric field within a chamber were examined using computer simulation, Nonconductive and con ductive models were constructed and experimental measurements obtained using both single-field (SF) and dual-field (DF) excitation. Results from computer simulations and in vitro measurements were compared to v alidate the proposed theoretical model of conductance-volume method, T he effects of field homogeneity and significance of parallel conductan ce in volume measurement a-ere then determined, The results of this st udy show that DF provide a more accurate measure of intraventricular v olume than SF, especially at larger volumes, However, both significant ly underestimate true volume at larger volumes, In addition, the paral lel conductance due to the chamber wall is significant at small volume s, but diminishes at larger volumes. Furthermore, the effect of parall el conductance beyond the chamber wall may be negligible. This study d emonstrates the limitations in applying current conductance technology to patients with dilated hearts.