Perspectives on Middle Ear Ventilatory Function: Lessons from the Eustachian Tube Function During Diving

Deficient middle ear ventilatory function is related to the pathogenesis of tympanic membrane atelectasis, serous and adhesive otitis media and cholesteatoma. Clinical and basic research studies focusing on middle ear barotrauma (MEB), which results from Eustachian Tube (ET) failure, might contribute to our understanding of the above mentioned common middle ear pathologies.
Middle ear barotrauma (MEB) is the main injury in sport and professional diving, involving 10 and 30% of experienced and novice divers, respectively.
The relation between mastoid pneumatization and MEB was prospectively investigated in a group of 66 submarine escape trainees. The magnitude of mastoid pneumatization per se was not found to be a critical factor in the pathogenesis of MEB. This supports the notion that mastoid hypopneumatization does not necessarily reflect poor ability to equalize middle ear pressure, and a well-developed mastoid air cell system is not always associated with good ET function.
We evaluated the effects of altered middle ear gas compositions and systemic hyperoxia on the ET ventilatory function to gain insights into the role of chemoreception in modulating tubal function and middle ear pressure. The results demonstrated a feedback control of middle ear pressure regulation by modulating ET function in response to changes in middle ear gas partial pressures. The intraluminal pressures required to dilate the ET and overcome the opposing periluminal pressures were higher under local or systemic hyperoxia. These higher pressures inhibit active opening by the tensor veli palatini muscle, particularly under conditions of relative negative tympanic cavity pressure. The consequences of pure oxygen diving on the human ET ventilatory function have been documented in a group of 34 closed-circuit oxygen divers. Seven hours post-diving, 63% of the ears showed malfunctioned aeration of the middle ear including tympanic membrane retractions of varying severity, middle ear effusions, sluggish or absent eardrum movement or type B tympanogram. These findings all cleared within 11 hours post-diving while breathing room air. These findings emphasize the role of middle ear cleft gas composition in controlling middle ear ventilatory function.