EFFECTS OF MIDDLE-EAR OXYGEN AND CARBON-DIOXIDE TENSIONS ON EUSTACHIAN-TUBE VENTILATORY FUNCTION

The objective of this study was to determine the effect of middle ear (ME) gas composition on eustachian tube ventilatory function (ETVF). E TVF was evaluated by using forced-response and inflation-deflation tes ts in four alert cynomolgus monkeys during test sessions with differen t gas compositions. The ME was flushed with one of the four gas mixtur es: 1. air; 2. 12% oxygen, 88% nitrogen; 3. 100% oxygen; and 4. 5% car bon dioxide, 21% oxygen, and 74% nitrogen before and during testing, T he results documented lower opening, steady-state, and closing pressur es, lower passive and active resistance, and greater dilatory efficien cy following ME flushes with the hypercarbic and hypoxic gas mixtures when compared to the others. Also, for applied ME overpressure, the ma ximum pressure change during a swallow, the average pressure drop for all swallows, and the percentage of the applied pressure equalized wer e greater under hypoxic and hypercarbic conditions. These results show that ME gas composition affects ETVF and support feedback modulation of ME pressure regulation.