Pressure-induced ossicular alterations in the oim mouse model of brittle bone disease do not cause hearing loss.

Abstract

The middle ear endures significant pressure variations during activities such as flying or diving, which can cause large displacements of the tympanic membrane and ossicles. While the middle ear of the general population usually withstands such displacements without impairing hearing function, little is known about the effects of sudden pressure changes in the middle ears of populations with connective tissue disorders, like osteogenesis imperfecta (OI or brittle bone disease). Similar to OI long bones, which fracture under minimal impact, we hypothesized that a sudden pressure change in the OI ear canal alters the ossicular chain integrity and impairs hearing function. Using the B6C3Fe a/a-Col1a1(oim/oim) mouse model of severe OI, this study determines the impact of sudden pressure changes in the ear canal on hearing function by testing auditory brainstem response (ABR) and verifying ossicular structural integrity using synchrotron microtomography. No differences in baseline thresholds were observed between oim/oim mice and wild-type (WT) controls, as well as no changes in hearing function after pressure exposure, measured as (i) the change in the neural response amplitude at the highest sound level (ΔRMS), (ii) the change in ABR threshold (ΔThreshold), and (iii) the change in latency of the first positive peak of the neural response at the highest sound level (ΔLatency). However, post-pressure, the middle ear ossicles of oim/oim mice showed twice the incidence of incudomalleal joint abnormalities compared to healthy WT ears (27% vs. 13%), with incudomalleal joint narrowing, fractures, and particularly fusions.