PRECONDITIONING THE TYMPANIC MEMBRANE - IDENTIFICATION OF CHOLESTEATOMA PRONE EARS

Preconditioning refers to changes in the mechanical properties of tiss ues due to repeated stress-strain experiments. Generally, after a numb er of cyclic deformation, a steady state is reached, where the experim ent becomes repeatable, and the specimen is preconditioned. Tympanomet ric measurements of middle ear compliance also show increasing values for repeated trials until after 5 or 6 measurements, where steady stat e is reached. However, in some normal cases with high compliance it ha s previously been found that the tympanic membrane is not always able to reach a steady state, but displays larger and larger compliance ove r trials. This property may be characterized as a decreased resistance against pressure loads, which may lead to retractions, atelectasis, a nd cholesteatomas. Preconditioning was investigated in a group of 21 p atients with cholesteatomas. Due to perforations and discharge the con tralateral 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 repea tability between trials with insignificant effect of preconditioning c an be obtained after 4 trials.