Mathematical model explaining the sources of error in certain estimates ofthe gas exchange constants for the middle ear

Mover-Lev and colleagues reported a carbon dioxide-oxygen time-constant rat io of 3.9 for transmucosal gas exchange in guinea pigs under conditions of a large positive oxygen pressure gradient and a negative carbon dioxide gra dient. That ratio is much less than the value of 19 reported previously for monkeys and used in predictive models of middle ear pressure regulation. I n this report, the mathematics that underlie models of transmucosal gas exc hange are developed and the conditions that allow accurate estimation of ti me constants are defined. The results demonstrate that the experimental and analytic methods used by Mover-Lev et al do not control for certain confou nding effects or concurrently measure all required system parameters. Under the most realistic conditions, their ratio of 3.9 represents a significant underestimation of a true value on the order of 10. Also, their expectatio n of nonvarying, transmucosal time constant ratios for pairings that includ e reactive gases is simplistic and true only for identical experimental con texts.