Wideband reflectance tympanometry in chinchillas and human.

Wideband reflectance tympanometry was performed on twelve chinchillas ears. The complex input impedance of the middle ear, multifrequency admittance tympanograms, reflectance patterns (reflectance versus frequency), and reflectance tympanograms (reflectance versus ear-canal air pressure) were analyzed and compared to human data. The complex impedance of the chinchilla ear has a lower stiffness reactance at low frequencies, a higher mass reactance at high frequencies, and a lower resistance compared to the human. Multifrequency admittance tympanograms from chinchillas follow the same sequence of patterns as humans for low frequencies (<2 kHz). At higher frequencies tympanograms from both species are poorly organized and do not follow a consistent sequence of patterns. Reflectance patterns of chinchillas and humans are different. However, both species show high reflectance at low frequencies, regions of lower reflectance in mid-frequencies (2-6 kHz), and high reflectance at high frequencies (>8 kHz). Reflectance tympanograms for the two species show a single, centrally located minimum at low frequencies (<2 kHz) and are substantially different at higher frequencies. Results are shown for two animals that underwent eustachian tube obstruction. Reflectance patterns obtained with different ear-canal air pressures are substantially different. Reflectance results at any single ear-canal pressure (including ambient pressure) do not completely characterize the effects of middle-ear pathology.