Preconditioning the tympanic membrane: identification of cholesteatoma prone ears?

Preconditioning refers to changes in the mechanical properties of tissues due to repeated stress-strain experiments. Generally, after a number of cyclic deformation, a steady state is reached, where the experiment becomes repeatable, and the specimen is preconditioned. Tympanometric measurements of middle ear compliance also show increasing values for repeated trials until after 5 or 6 measurements, where steady state is reached. However, in some normal cases with high compliance it has previously been found that the tympanic membrane is not always able to reach a steady state, but displays larger and larger compliance over trials. This property may be characterized as a decreased resistance against pressure loads, which may lead to retractions, atelectasis, and cholesteatomas. Preconditioning was investigated in a group of 21 patients with cholesteatomas. Due to perforations and discharge the contralateral ear was measured. Nine tympanometries were recorded in one sequence. The increase in compliance between trials showed a complete overlap with a group of 25 normal subjects. For both groups good repeatability between trials with insignificant effect of preconditioning can be obtained after 4 trials.