Finite element analysis of active Eustachian tube function.

The inability to open the collapsible Eustachian tube (ET) has been related to the development of chronic otitis media. Although ET dysfunction may be due to anatomic and/or mechanical abnormalities, the precise mechanisms by which these structural properties alter ET opening phenomena have not been investigated. Previous investigations could only speculate on how these structural properties influence the tissue deformation processes responsible for ET opening. We have, therefore, developed a computational technique that can quantify these structure-function relationships. Cross-sectional histological images were obtained from eight normal adult human subjects, who had no history of middle ear disease. A midcartilaginous image from each subject was used to create two-dimensional finite element models of the soft tissue structures of the ET. ET opening phenomena were simulated by applying muscle forces on soft tissue surfaces in the appropriate direction and were quantified by calculating the resistance to flow (R(v)) in the opened lumen. A sensitivity analysis was conducted to determine the relative importance of muscle forces and soft-tissue elastic properties. Muscle contraction resulted in a medial-superior rotation of the medial lamina, stretching deformation in the Ostmann's fatty tissue, and lumen dilation. Variability in baseline R(v) values correlated with tissue size, whereas the functional relationship between R(v) and a given mechanical parameter was consistent in all subjects. ET opening was found to be highly sensitive to the applied muscle forces and relatively insensitive to cartilage elastic properties. These computational models have, therefore, identified how different tissue elements alter ET opening phenomena, which elements should be targeted for treatment, and the optimal mechanical properties of these tissue constructs.

Effect of surface tension and surfactant administration on Eustachian tube mechanics.

Development of otitis media has been related to abnormal Eustachian tube (ET) mechanics. ET is a collapsible tube that is periodically opened to regulate middle ear pressure and to clear middle ear fluid into the nasopharynx. The ability to perform these physiological functions depends on several mechanical properties, including the ET's opening pressure (P(open)), compliance (ETC), and hysteresis (eta). In this study, a previously developed modified force-response protocol was used to determine ET mechanical properties after experimental manipulation of the mucosal surface condition. Specifically, these properties were measured in the right ear of six cynomologous monkeys under baseline conditions after "washing out" the normal ET mucous layer and after instillation of a pulmonary surfactant, Infasurf. Removal of the normal mucosa did not significantly alter P(open) but did result in a decrease in ETC and eta (P < 0.05). Treatment of the mucosa with Infasurf was effective in reducing P(open) and increasing both ETC and eta to baseline values (P < 0.05). These results indicate that the mucosa-air surface tension can affect the overall ETC and eta properties of the ET. In addition, this study indicates that surfactant therapy may only be beneficial in patients with rigid or inelastic ETs (large P(open) and low ETC and eta).