Objective: The total pressure in the middle ear depends on the air composition of this gas pocket, i.e. on gas exchanges occurring through either the Eustachian tube (ET) or mucosa. The aim of this study was to develop an experimental model to investigate the exclusive role of trans-mucosal gas exchanges in the middle ear (ME).
Material and methods: Both tympanic membranes of 20 Sprague-Dawley rats were punctured under general anesthesia. Rats were divided into two equal groups. Group 1 had no ET obstruction. In Group 2, the ET was blocked, after velar incision, by cauterization and application of cyanoacrylate glue into the lumen. One open transparent glass tube containing a droplet of colored water was placed horizontally and connected hermetically to each ear canal. The ME was then flushed with room air through the tube. Variations in ME gas volume were measured by reading the displacement of the liquid droplet in the horizontal tube. The kinetics of variations in gas volume between groups were displayed and statistically compared using a two-sided t-test.
Results: The pattern of variations in ME gas volume with time was similar in the two groups. Both were characterized by a decrease with three phases and an elimination rate of approximately 0.152 +/- 0.026 microl/min. There was no significant difference in the mean rate of ME volume changes between the two groups.
Conclusion: This experimental model allows investigation of trans-mucosal gas exchanges. These exchanges exhibit an absorptive function resulting in a negative pressure that must be compensated, under physiological conditions, by air flow through the ET.