Measures of middle ear admittance during experimentally induced changes in middle ear volume in the hamster

The relation between middle ear admittance measured at the tympanic membrane and middle ear volume was studied in adult hamsters. A modified tympanometric procedure was used to measure complex admittance at eight test frequencies. Middle ear volume was varied by injecting small amounts of water into the bulla cavity. As bulla volume decreased, the value of admittance magnitude also decreased. The measured values of admittance magnitude could be accurately predicted by the equation for admittance magnitude until the bulla was about 70% filled. The results confirm that measures of middle ear admittance reflect the volume of the middle ear cavity as would be expected of a pure compliance. Where such measures are available in man, they might be used to predict the degree of fluid intrusion into the middle ear cavity.