Analysis by finite element method of dynamic characteristics of the external ear canal in neonates

Abstract

Although early diagnosis and treatment of hearing disorders in neonates is highly effective for realization of linguistic competence and intellectual development, the diagnostic accuracy in the initial period of life is low. To overcome this problem, extensive research studies to diagnose the neonatal hearing with tympanometry, multifrequency tympanometry, the wideband acoustic transfer function technique, the sweep frequency impedance (SFI) technique and others have been conducted. However, since the results obtained are not consistent with those obtained in adults/children, diagnosis of hearing in neonates has been problematic. The difference in the dynamic characteristics of the hearing apparatus between adults/children and neonates, especially due to the morphological difference in the external ear canal, has been suggested as a possible reason for such problem. However, the dynamics of the neonatal hearing system has not yet been clarified. In the present study, therefore, three types of finite-element models of the neonatal external ear were developed and their dynamic characteristics (i.e., natural frequencies and mode shapes) were investigated. Frequency analyses of the constructed models revealed that the neonatal external ear canal wall has a resonance of around 0.3 kHz and that this resonance leads to the volume change of such canal. This result suggests that the neonatal external ear canal wall may exhibit intrinsic oscillatory behavior if conventional tympanometry with a probe tone of 226 Hz is performed, affecting the diagnostic data in neonates.