1996 Volume 39 Issue 2 Pages 145-149
The subjects of this study were 22 patients (24 ears) with otitis media with effusion who had type C or type B tympanograms. Their mean age was 48.7 years; they were relatively old patients with otitis media with effusion.
The method employed to measure the pH of the middlev ear exudate consisted of incising the tympanum under iontophoretic anesthesia, inserting an antimony pH meter into the exudate fluid in the tympanic cavity through the incision, and recording the exudative fluid pH value afterthe readings stabilized.
The measurements obtained showed that the pH of exud te in otitis media with effusion never exceeded 7.4, averaging 7.05±0.27, and there seemed to be 12 ears with type B tympanograms among those with a pH of 7.0 or less.
A simple middle ear cavity gas model was created by mixing carbon dioxide gas in a fixed volume of air at an overall ratio of 6%, and a phenomenon was observed whereby solubility of carbon dioxide gas varies with the ratio between the volume of gas and the volume of fluid in the vessel.
This suggests that one of the reasons for the negative pressure in the middl ear in otitis media with effusion may be that exudate solubility varies depending on the ratio between middle ear cavity gas volume and exudative fluid volume, and this may promote the development of negative pressure, paralleling inhibition of middle ear mucosa gas metabolism.
Thus, it was concluded that, depending on the stage of the disease, the ratio between the volume of middle ear cavity exudative fluid and gas volume plays a major role in creating negative pressure in the middle ear cavity, giving rise to variety of negative pressure patterns.
