Effects of Middle Ear Oxygen and Carbon Dioxide Tensions on Eustachian Tube Ventilatory Function

Abstract

The objective of this study was to determine the effect of middle ear (ME) gas composition on eustachian tube ventilatory function (ETVF). ETVF was evaluated by using forced-response and inflation-de-flation tests in four alert cynomolgus monkeys during test sessions with different gas compositions. The ME was flushed with one of the four gas mixtures: 1. air; 2. 12% oxygen, 88% nitrogen; 3. 100% oxygen; and 4. 5% carbon dioxide, 21% oxygen, and 74% nitrogen before and during testing. The results documented lower opening, steady-state, and closing pressures, lower passive and active resistance, and greater dilatory efficiency following ME flushes with the hypercarbic and hypoxic gas mixtures when compared to the others. Also, for applied ME overpressure, the maximum pressure change during a swallow, the average pressure drop for all swallows, and the percentage of the applied pressure equalized were greater under hypoxic and hypercarbic conditions. These results show that ME gas composition affects ETVF and support feedback modulation of ME pressure regulation.

Effects of Systemic Hyperoxia on Eustachian Tube Ventilatory Function

“…Suggested sensory components of the proposed neural pathways have been identified in the tympanic cavity mucosa and eustachian tube muscle fibers 5‐7,17 . We have previously shown that exposure of the tympanic cavity to a hyperoxic gas mixture reduced middle ear pressure equalization ability when compared with hypercarbic and hypoxic mixtures 8 . The possible role of changes in the systemic oxygen tension on ETVF control has not yet been studied.…”

“…The monitoring system and test protocols have been described previously and have been employed for ETVF evaluation in humans and several mammal species including the cynomolgus monkey 8‐11 …”

“…In a recent study, induction of middle ear hyperoxia was shown to down‐regulate the ETVF in cynomolgus monkeys when compared with hypercarbic and hypoxic mixtures 8 . These observations support ETVF modulation in response to changes in middle ear gas partial pressures.…”

Can Eustachian Tube Ventilatory Function Impairment After Oxygen Diving Be Influenced by Application of Free Radical Scavenger Vitamins C and E?

“…It has been suggested that downregulation of the eustachian tube opening function during systemic hyperoxia is possibly caused by a chemoreceptor tissue response. 20 …”

The Role of Vestibular Testing in the Evaluation of Patients Engaged in Occupations in Non-Terrestrial Conditions

“…The supine and head-down positions frequently assumed in diving further contribute to venous congestion and difficulties in ear clearing [6]. Oxygen-enriched breathing gas mixtures often employed in diving and military flying further reduce middle ear ventilation secondary to mucosal oxygen toxicity or downregulation of chemoreceptor-mediated eustachian tube ventilatory function [7][8][9]. These physiological disadvantages, when combined with too rapid a pressure change, in the absence of active attempts to achieve pressure equalization by Valsalva or similar manoeuvres or in the presence of local inflammation and mucosal swelling, will lead to middle ear barotrauma.…”