VOLUME PROFILES OBTAINED BY A CONDUCTIMETRIC METHOD

One problem faced by intracardiac conductance volumetry is the non-uni form distribution of the injected current. Salo, in 1989, proposed a m ethod to correct this undesirable effect. The objective here is to tes t Salo's method in known volumes of simple geometry by obtaining volum e profiles. A plastic rod with 15 metallic rings simulated the conduct ance catheter. Five sections were used for the resistance measurements employing the upper electrode as fixed current source and the lowest one as the shifting source. This is part of Salo's procedure. The sour ce-to-section distance was measured from the moving source to the sect ion (linear definition) or using the equivalent distance concept (Salo 's). Thereafter, each sectional resistance set of values was plotted a s a function of the inverse of the source-to-section distance (either definition) elevated to an empirical exponent k to obtain the correcte d sectional resistance by extrapolation back to zero of the regression line, i.e., a value produced by a source theoretically placed at infi nity. In addition, a mathematical analysis was attempted, searching fo r an optimum k based on minimum volume error. The best volume profiles for two cylinders and a frustum were obtained with k = 2 using the li near definition of distance (errors of -3.49%, -1.25% and -3.65% respe ctively). Moreover, the frustum angle was determined within 0.4-degree s (2.7%) of the real value. The theoretical analysis led to an inverse logarithmic relationship between the exponent k and the source-to-sec tion distance. In conclusion: (1) The linear definition of source-to-s ection distance applying Salo's correction with k = 2 produced the sma llest errors, both in volume and angle estimations; (2) there is no op timum k; (3) for very large distances, k tends to a low value (about 0 .8); (4) for heart sizes, k = 2.1 can be suggested for all sections.