Random walk type models for indicator-dilution studies: comparison of a local density random walk and a first passage times distribution.

The relative merits of the local density random walk and the first passage times distributions were compared with respect to their practical applicability in cardiovascular research and clinical practice. Open indicator-dilution curves of varying shape were used, and reference values for area and mean transit times were calculated numerically. Curves not perturbed by recirculation were obtained in two different ways. Thermodilution curves were obtained in an animal model at the left and the right side of the heart respectively and conductivity curves with 0.5% NaCl solution as indicator were obtained in a hydrodynamic circulation model. The fits of the two types of distribution were equally accurate for the more symmetrical curves; for very skewed curves the local density random walk fit proved to be more accurate. This result could be related to the greater difference in shape between the first passage times and local density random walk distribution for a large degree of asymmetry. For this reason the local density random walk distribution for fitting indicator-dilution curves was used in a variety of other experimental conditions.