Effect of exogenous surfactant on eustachian tube function in the rat

Three solutions, surfactant prepared from pig lungs, a mixture of synthetic phospholipids, and saline solution, were instilled into the middle ears of rats. The middle ear pressure necessary to force the eustachian tube open was studied. Ten minutes after instillation of pulmonary surfactant there was a 0.58 +/- 0.10 kPa decrease in the pressure opening level (P less than .001). The reduction persisted throughout the 50-minute experiment. There was also a reduction 0.17 +/- 0.16 kPa in the pressure opening level (P less than .01) after the administration of the synthetic phospholipid mixture. This reduction was significantly less than the reduction produced by the pulmonary surfactant. No decrease in the pressure opening level was seen after the instillation of saline solution into the middle ear cavity. The fact that surfactants are demonstrable in the middle ear and eustachian tube, coupled with these findings of an effect on the tubal opening, suggests a physiologic role for surface tension-lowering substances in tubal function.