A model to explain the rapid pressure decrease after air-inflation of diseased middle ears

Objectives: Air-inflation in humans and monkeys with significant negative m iddle ear pressure or with middle ear inflammation was shown to cause great er than ambient middle ear pressure initially, followed by a rapid rate of pressure decrease to approach the preinflation value. Study Design: A mathe matical model of middle ear pressure regulation is presented and used to si mulate air-inflation of the normal and diseased middle ear. Materials and M ethods: The model represents the total volume of the middle ear as consisti ng of three subcompartments representing the airspace, effusion, and mucosa /blood. Gas exchange among those compartments was assumed to be diffusion l imited, and the gas exchange between the mucosa/blood compartment and syste mic blood was assumed to be perfusion limited. Disease was modeled as an in crease in mucosal blood flow or, alternatively, as an increase in the volum es of the effusion and mucosa/blood compartments. Results: The predictions of the model agree better with the experimental data when the increased rat e of pressure change after middle ear inflation in diseased ears is driven by an increased volume of the effusion compartment as opposed to an increas ed perfusion rate. The responsible mechanism is a rapid redistribution amon g subcompartments of the gas volume introduced into the air compartment. Co nclusions: These results suggest that middle ear inflation with inert gas c an be used to diagnose the presence and relative amount of middle ear effus ion, and that current protocols for treating otitis media with effusion usi ng inflation need to be modified to optimize their intended effect.