Anomalous middle ear gas absorption in a non-human primate model of cleft palate.

Following surgical clefting of the palates of nine Rhesus monkeys (Macaca mulatta), daily recordings of the middle ear pressure by tympanometry have shown fluctuations between high positive and negative values. High positive middle ear pressures were recorded during the recovery from otitis media, and it was suggested that these pressures were the result of a learned or reflexive autoinflation of the middle ear cavity. To test this hypothesis, animals presenting high positive middle ear pressures were anesthetized with sodium pentobarbital, and serial tympanograms were obtained at 5-minute intervals for a period of four hours. The results showed a substantial and rapid decrease in middle ear pressure following anesthesia (200 to 400 mm H2O). These findings were compared to those of similar experiments in normal animals, with near zero resting middle ear pressures or following air and oxygen politzerizations. The changes in middle ear pressure of cleft palate animals were significantly greater than those recorded for normal animals with near zero resting middle ear pressure and were essentially the same as those recorded for normal animals following air politzerization. These data suggest that abnormally high positive middle ear pressures are the result of an introduced bolus of air. This mechanism may serve as a means of ventilating the middle ear cleft in lieu of a debilitated active dilatory mechanism, and as such, may aid in the resolution of the middle ear effusion.