Introduction: Middle ear (ME) pressure-regulation (MEPR) is a homeostatic mechanism that maintains the ME-environment pressure-gradient (MEEPG) within a range optimized for “normal” hearing.
Objective: Describe MEPR using equations applicable to passive gas-exchange and determine if the predictions of that description include the increasing ME pressure observed under certain conditions and interpreted by some as evidencing gas-production by the ME mucosa.
Methods: MEPR was modeled as the combined effect of passive gas-exchanges between the ME and: perilymph via the round window membrane, the ambient environment via the tympanic membrane, the local blood via the ME mucosa and the NP during Eustachian tube openings. The first 3 of these exchanges are described at the species level using Fick's diffusion equation and the last as a bulk gas transfer governed by Poiseuille's equation. The model structure is a time-iteration of the state equation: PME g(t=(i+1)∆t) = ∑s(PME s(t=i∆t) + (1/(βME sVME)∑P(ҚP s(PC s(t=(i∆t)-PME s(t=(i∆t))). There, PME g(t=i∆t) and PME s(t=i∆t) are the ME total and species-pressures at the indexed times, PC s(t=i∆t) is the species-pressure for each exchange-compartment, βME sVME is the product of the ME species-capacitance and volume, ҚP s is the pathway species-conductance, and ∑S and ∑P are operators for summing the expression over all species or exchange pathways.
Results: When calibrated to know values, the model predicts the empirically measured species-pressures and the observed time-trajectories for total ME pressure and the MEEPG under physiologic, pathologic and non-physiologic conditions.
Conclusions: Passive inter-compartmental gas exchanges are sole and sufficient to describe MEPR and, by Occam's Razor, discount gas-production by the ME mucosa.
