A tympanometric evaluation of middle‐ear development in neonatal hamsters

Abstract

Tympanometry was used to follow the maturation of middle‐ear function in neonatal hamsters from 6 to 80 days of age. Subjects in each of seven age groups were anesthetized, mounted in a head holder, and the tympanic ring and auditory bulla were exposed surgically. The bulla was ventilated with small bore nylon tubing in order to equalize middle‐ear pressure to ambient pressure. A tympanometer probe was sealed directly over the tympanic membrane using a short piece of rubber tubing to couple the probe to the tympanic ring. The magnitude of relative acoustic impedance was measured at frequencies between 1.0 and 1.5 kHz. Relative acoustic impedance was the difference between the impedance measured when the tympanic membrane was stressed with a pressure of +200 mm H2O and the minimum impedance that could be obtained as the pressure was reduced. There was no measurable impedance magnitude difference on day six, but by day 15 small though reliable values could be obtained. Thereafter, impedance magnitude changed rapidly and reached a plateau after 33 days. No further changes were noted in 77‐day‐old animals which were considered to be adults. Results will be discussed with regard to the maturation of middle‐ear morphology and inner‐ear physiology. [Supported in part by the NSF and the Deafness Research Foundation.]