The influence of pregnancy on the eustachian tube function in rats

Textbooks of otorhinolaryngology usually report that one-third of women diagnosed for patulous Eustachian tube (tuba aperta) are pregnant or on estrogenic therapy. To investigate whether the opening of the Eustachian tube (ET) can be facilitated experimentally during pregnancy, the ET opening function of 14 pregnant rats was compared with that of 14 nonpregnant controls. The air pressure at which the ET opened (the pressure opening level, Pol) when air is injected into the middle ear, and the pressures maintaining open ET during continued air injection were measured. The Pol was lower in the pregnant rats, whereas there was no difference in pressures between the two groups during open ET. The differences between Pol and the pressures during open ET were smaller in the pregnant rats than in the controls. It was furthermore demonstrated in 2 rats that, after instillation of a surface tension lowering substance in the middle ear, the Pol was reduced markedly, whereas the effect on the pressure during open ET was less pronounced. It is concluded that pregnancy facilitates opening of the ET in rats and it is suggested that it is done by reducing the surface tension of the ET secretion.