Measurement of the viscoelastic compliance of the eustachian tube using a modified forced-response test

Objectives: Eustachian tube compliance (ETC) was suggested to be an important determinate of function. Previous attempts to quantify ETC used summary measures that are not clearly related to the physical properties of the system. Here, we present a new method for measuring ETC that conforms more closely to the engineering definition of compliance. Methods: The forced response test was modified to include oscillations in applied flow after the forced tubal opening. Pressure and flow were recorded during the standard and modified test in 12 anesthetized cynomolgus monkeys. The resulting pressure–flow, hysteresis loops were compared with those predicted by a simple fluid-structure model of the Eustachian tube with linear-elastic or viscoelastic properties. The tubal compliance index (TCI) and a viscoelastic compliance (Cv) were calculated from these data for each monkey. Results: The behavior of a viscoelastic, but not a linear elastic model accurately reproduced the experimental data for the monkey. The TCI and Cv were linearly related, but the shared variance in these measures was only 63%. Conclusions: This new method for measuring ETC captures all information contained in the traditional TCI, but also provides information regarding the contribution of wall viscosity to Eustachian tube mechanics.