Tympanometric configurations and middle ear findings in experimental otitis media.

Relationships between ventilation of the middle ear (ME) system and pathogenic bacteria in the upper respiratory tract were explored in an animal model to better understand the etiopathogenesis of otitis media. Otitis media developed in 12 of 18 chinchillas inoculated intranasally with Streptococcus pneumoniae followed by bilateral ME deflation (negative pressure). Otitis media with effusion developed in 19 of 36 ears examined ten days after inoculation. The development of purulent effusion after ten days was highly correlated with persistent negative ME pressure for at least 48 hours after deflation, while most ears that developed serous effusion after ten days had normal ME pressure 48 hours after deflation. Tympanometric validation of the presence of absence of effusion and type of effusion was obtained ten days after inoculation. A low compliance tympanogram detected 90% of the purulent effusions and was 100% specific for this type of effusion. In contrast. three of four serous effusions were associated with normal pressure/normal compliance tracings suggesting that the physical characteristics or volume of ME effusion and/or the histopathology of the ME cleft are reflected i the tympanometric configuration.