Experimental Audiometry

1. Numerical modeling of the traveling wave propagation in the cochlea for the calculation of the cochlear amplifier, which enables sensitive hearing down to sound pressure levels of only 20 µPa and lower in case of healthy human hearing. One of the results is the confirmation of a biologic parametric amplifier, realized by outer hair cells of the organ of Corti which is responsible for the high sensitivity in the healthy case (Böhnke, 2019).

2. Examinations of the vibrational behavior of the healthy and pathologic middle ear with acoustic stimulation and diagnostics by contact free measurements (tympanometry) and short latency evoked electric potentials (BERA, Brainstem Evoked Response Audiometry) by registration of electric potentials at the scalp.

3. Development of a new measurement system for the otological diagnostic
The knowledge of the eardrum displacement is important for a precise diagnostic of the hearing system, especially of the middle- and inner ear (cochlea). This fact was already established by a dissertation of a former coworker of this working group from 1980 to 2015 Mr. Thomas Janssen, who established this in connection with the signals the BERA. Therefore we develop in connection with the medical-technologic industry a system for measuring the sound pressure in the ear canal to measure the eardrum admittance (immitance) to gain improved diagnostic possibilities as shown by an actual work from Kiel and Hamburg in Germany (Mewes und Wiesner 2020). 

The results of the first mentioned research area are for the benefit of patients with residual hearing at low frequencies (f < 300 Hz), because the signal processing at these frequencies enables patients with cochlea implants to improve the speech recognition in disturbing noise by Electro-Acoustic Stimulation, EAS). 

Another project concerns the objective middle ear diagnostic, which is done either visually or by tympanometry up to now. The contact free analysis of eardrum vibrations using a Laser-Doppler Vibrometer enables a more refined distinction of different middle ear pathologies. The following image shows the mechanical-mathematical model including the Floating Mass Transducer (FMT) of the company MED-EL (Vibrant-Soundbridge, Austria) applied at the long process of the incus of the middle ear for the calculation of the response.

The success of the supply by an middle ear implant hearing aid is highly dependent  on the quality of coupling of the electromechanical transducer (the FMT). Up to now there was no measurement procedure to quantify this. The work of another M.D, dissertation of Ms. Katja Böck (Measurement of eardrum displacements for coupling quality of middle ear implants, 2020) establishes the postoperative control using FMT.

These measurements require a commercial Laser-Doppler Vibrometer with high costs (approx. 5 k€). Therefore we work on the development of a new acoustic measurement system which also enables the measurement of a part of a million meters  (10-9 m) which is expected to be more attractive in price.

• Böhnke F (2015), Nonlinear Distortions and Parametric Amplification Generate Otoacoustic Emissions and Increased Hearing Sensitivity, Acoustics, MDPI
• Janssen T, Untersuchung des Einflusses der Reizpolarität und Reizdauer auf die Auslösung früher akustisch evozierter Potentiale der Hörbahn durch Messung und Modellrechnung, Dissertation 1989 an der TU Berlin, Germany.
• Mewes A, Wiesner T (2020), Breitbandige Immittanz-Messungen Teil I: Messtechnische Grundlagen und Messergebnisse bei Erwachsenen, Zeitschrift für Audiologie, Jahrgang 59, Nr. 2 
• Böhnke F, Bretan T, Lehner S, Strenger T (2013) Simulations and Measurements of Human Middle Ear Vibrations Using Multi-Body Systems and Laser-Doppler Vibrometry with the Floating Mass Transducer Materials 2013, 6, 4675-4688; doi:10.3390/ma6104675
• Strenger T, Brandstetter M, Stark T, Böhnke F (2018), Neue klinische Anwendungen der Laser-Doppler-Vibrometrie in der Otologie, Ausgabe 4, HNO
• Braun K, Böhnke F, Stark T (2012) Three-dimensional representation of the human cochlea using micro-computed tomography data: Presenting an anatomical model for further numerical calculations, Acta-Otolaryngologica, vol. 132, no. 6, 603-613
• Böck K (2020) Optische Messungen von Trommelfellbewegungen für die Entwicklung objektiver Anpassverfahren von Mittelohr-Hörimplantaten, Dissertation an der Medizinischen Fakultät der Martin-Luther-Universität, Halle-Wittenberg

• Bacherlorthesis: Numerical examinations of sound propagation in tubes, Konrad Schneider (cand. B.Sc., TU Munich, Germany)
• Masterthesis: Construction of an ear canal simulator for measuring the mechanical eardrum impedance for measuring the sound pressure in the time and frequency domain, Maria Meindl (B.Sc., TU Munich, Germany)
• Dissertation M.D. (expected starting September 2020): Measurement of Acoustical Evoked Potentials from the Human Scalp for the Analysis of Electric Responses in the Cochlea, Fang Wang (M.Sc. Medicine) Central South University (CSU), Xiang Ya School of Medicine, China