Middle ear gas volume variations: Transmucosal exchanges in inflamed ears

Abstract

Problem: Gas exchanges in the middle ear (ME) are thought to be the cornerstone in the development of atelectasis and cholesteatoma. The purpose of the current study was to evaluate the transmucosal gas exchanges in the ME in inflamed conditions. Methods: We have designed an experimental model in order to study transmucosal gas exchanges. Volume variations measurements of the gas content of the ME are recorded at constant pressure and temperature in rats under general anesthesia. Twenty-five rats were divided into 2 groups. In group 1 (n = 16), inflammation was induced by transtympanic injection of 25 μL of lipopolysaccharide (LPS) serotype 026:B6 from E coli (1 mg/ml) with vehicle (150 mM NaCl, 10 mM phosphate buffer, with similar pH and osmolarity). Group 2 (n = 9) served as control. Animals were studied for 3 days after the injection. Bullae were then harvested, fixed in 10% phosphate-buffered formalin, decalcified with 10% EDTA buffer, embedded in paraffin wax, cut, and stained with hematoxin-eosin. The mucosa thicknesses between the groups were compared using a 2-sided t test. Statistical significance was set at P = 0.05. Results: In group 1, the kinetics of the rat ME gas volume variations exhibited a linear decrease (-0.098 μL min-1 ± 0.031) which was significantly higher ( P = 0.01) than that observed in group 2 (-0.061 μL min-1 ± 0.033). The mucosa thickness was significantly higher in inflamed ears (group 1, Le = 48.4 μm ± 11) than in noninflamed ears (group 2, Le = 20.5 μm ± 10.1). Conclusion: Significant increases of transmucosal gas exchanges were associated with thicker mucosa in inflamed ears. Significance: Further studies using mathematical modeling will help evaluate the respective role of the ME circulation and the ME mucosa in this process. Support: None reported.