Open Access

Bastian Baselt

• This dissertation investigated the acousto-vibratory function of the human tympanic membrane (TM) in normal, pathological, and reconstructed conditions using experimental measurements and clinical data. The validity of fresh-frozen human cadaveric temporal bones, which were used for experimental work in this study, was assessed by comparing middle-ear transfer functions (METF) with the METF of fresh specimens, employing rational polynomial fitting to preserve individual curve characteristics. A new method for three-dimensional TM motion measurement was developed by combining scanning laser Doppler vibrometry (SLDV) from multiple orientations with micro-computed tomography (μCT) for reconstruction of the TM surface and registration into the anatomical frame, enabling extraction of normal and tangential motion components. Full-field three-dimensional TM motion under induced pathological conditions including thickening and perforations on the TM was characterized using a novel 3D-SLDV system. The influence of perforation characteristics and patient factors on hearing loss and tympanoplasty outcomes was examined in a clinical study using multivariate statistical analysis. Fresh-frozen specimens showed small but consistent differences from fresh temporal bones, validating their use for comparative studies despite presumed mild stiffening of the middle-ear structures in fresh-frozen temporal bones. Three-dimensional measurements of intact TMs revealed near in-phase motion at low frequencies and increasingly complex patterns at higher frequencies with inward-traveling waves at the periphery. Tangential motion components around the manubrium remained consistently 5–10 dB smaller than normal components across the frequency spectrum and throughout all pathological conditions, indicating minimal contribution of the tangential component to ossicular drive. TM thickening produced localized effects beneath the thickened area with spatial smoothing of motion patterns. Perforations primarily affected umbo motion in a size-dependent manner at low frequencies, which was restored upon closure, while global motion patterns were largely preserved across pathological conditions. The clinical study identified perforation size as the primary factor influencing hearing loss, spontaneous closure rates, and surgical outcomes, with additional significant contributions of mucosal health, bilateral ear status, and etiology. This work validates the use of fresh-frozen temporal bones for middle-ear mechanics research and establishes a new method for three-dimensional TM motion measurement, providing essential tools for future investigations. The findings enhance the mechanistic understanding of TM functions by demonstrating that tangential motion components contribute minimally to sound transmission under both normal and pathological conditions, and that global vibrational patterns are largely preserved despite local pathologies. Low-frequency hearing deficits in perforation result from acoustic shunt effects, while perforation characteristics alone do not fully explain hearing loss and surgical outcomes. The integration of three-dimensional vibrational data with clinical findings provides valuable validation for computational models and advances the understanding of sound transmission through pathological TMs.