The effect of gestation on eustachian tube function in rats.

Patulous Eustachian tube (tuba aperta) is a distressing condition for the patient with such symptoms as autophony and a sensation of fullness in the ear. One-third of women with the diagnosis are pregnant or taking oestrogens. To study whether opening of the Eustachian tube is facilitated during pregnancy, the tube opening function of 14 pregnant rats was compared with that of 14 non-pregnant controls. The middle ear air pressure at which the tube opened (the pressure opening level, Pol) was lower in pregnant rats than in controls; and the difference between Pol and the pressure during open tube (at continued air injection) was less in the pregnant rats. In two additional rats it was then demonstrated that instillation of a surface tension lowering substance in the middle ear caused similar pressure changes as occur during pregnancy. It is concluded that opening of the Eustachian tube in rats is facilitated in pregnancy, and it is suggested that this is due to a reduction in surface tension of the Eustachian tube secretion.