Sources of conductance volumetric measurement errors

The purpose of this work was to theoretically analyze the principles of conductance volumetric measurements, and to provide explanations and predictions of error sources. Cardiac volume measurements, based on conductance volumetric techniques have produced inconsistent and conflicting results. To enable more accurate evaluation of these results, we identified and analyzed four sources of measurement error: a) ventricular shape approximation; b) parallel conductance volume; c) non-measurable residual volume; and d) eccentric catheter position. Using a theoretical approach, based on modeling and simulation, we defined the properties of the two basic parameters of conductance volumetric calculations — the gain factor, α, and parallel conductance volume, α∗Vc. We found that α must be <1 and decreases with increasing volume. α∗Vc depends upon the myocardium/blood resistivity ratio. For volumes >40ml, α∗Vc decreases with volume. The contributions of these parameters to volumetric measurement error were determined.