EFFECTS OF SYSTEMIC HYPEROXIA ON EUSTACHIAN-TUBE VENTILATORY FUNCTION

Middle ear negative pressure and effusions, decreased middle ear compl iance, and abnormal tympanometry results have been described after div ing on oxygen. Middle ear gas hyperoxia has been shown to down-regulat e the eustachian tube ventilatory function (ETVF). The purpose of the present study was to investigate to what extent systemic hyperoxia in the face of air-equivalent middle ear gas composition might interfere with the ETVF. ETVF was investigated in four young adult female cynomo lgus monkeys by the forced-response and inflation-deflation tests usin g air while the animals breathed either room air or 100% normobaric ox ygen. Higher opening, closing, and steady-state pressures were observe d under systemic hyperoxia. The percentage of the applied pressure equ alized, and the maximal pressure change on a single swallow in the def lation test were both lower under hyperoxic conditions. The results sh ow that systemic hyperoxia might impair ETVF. This observation adds to our understanding of the pathophysiology of middle ear dysfunction ob served after diving on oxygen.