Parallel conductance estimation by hypertonic dilution method with conductance catheter: Effects of the bolus concentration and temperature

The conductance catheter has gained momentum since its introduction in card iovascular dynamics back in 1980, However, measuring errors are still blurr ing its clinical acceptance. The main objective here was to study the effec ts of the injected saline concentration and temperature on the evaluation o f the parallel conductance, G(p), and thus, on the correction volume V-p. T hat conductance, G(p), and its associated volume, V-p, were computed using 167 saline dilution curves obtained with boluses at different concentration s and temperatures, injected in seven anesthetized closed-chest dogs. The e xcursion of the total conductance relative to the steady-state value during a saline maneuver showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive ma neuvers, at 6-M concentration and at body temperature; therefore, the metho d acted as its own reference. The variation of V-p relative to the referenc e value nas clearly dependent on the injected concentration and on its temp erature; dispersion was greater at 22 degrees C than at 40 degrees C, The v ariability would recognize also other causes, such as uncertainty of the ex trapolation procedure and the thoracic redistribution of electrical field l ines. As conclusion, it is recommended to characterize each maneuver by its concentration and temperature. Body temperature and 6-M concentration appe ar as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the V-p estimation procedure in order to minimize errors. The variability of V-p, in different experime ntal conditions, demonstrated that both concentration and temperature are a dditional parameters that mag modify the G(p) estimate.