Mechanics of the middle ear system: age-related changes in viscoelastic properties

Morphological studies of age-related changes in the tympanic membrane have suggested a decreased elasticity for increasing age, whereas age-related changes in admittance measured by tympanometry have revealed inconsistent results. In this study we report on the viscoelastic properties of the middle ear system by means of a new method in two different age groups. This method measures hysteresis (microJ), which describes the viscous properties of the system, and compliance (mm(3)/kPa) reflecting its elasticity. Moreover, P(ec0) (kPa) was recorded, which corresponds to middle ear pressure measured by tympanometry. Recordings were made in a group of 30 older normal subjects (mean age 77 years) and results were compared to previous findings in a group of 39 younger normal subjects (mean age 29). Hysteresis was markedly decreased in the older normal group compared to the younger one (p = 0.057). This may reflect morphological changes previously reported in the tympanic membrane and can be related to theoretical considerations on tympanic membrane rupture pressures. Compliance and P(ec0) were not influenced by variation in age (p = 0.645 and 0.966).