Development of an Improved Round Window Stimulation Device to Treat Hearing Loss

Abstract

Hearing loss affects 14-15% of the US adult population, and can be caused by conductive, sensorineural or mixed pathologies; however, the contribution of these pathologies has not been quantified. Furthermore, recent studies show that conductive and mixed hearing loss can be treated by direct mechanical stimulation of the round window, though a reliably effective device is not available. To improve round window stimulation treatment, we performed several investigations. The first was to quantify the types of hearing loss treated at the Massachusetts Eye and Ear hospitals. Hearing loss categories included: sensorineural, surgically-treatable conductive, acute otits media, earwax buildup, and unknown. Sixteen percent of cases were diagnosed with surgically-treatable conductive hearing loss. Conventional treatment for such cases includes hearing aids or middle ear surgery, which restores movement or continuity of the conductive pathway. However, in some cases, where conventional surgery is unsuitable or unsuccessful, round window (RW) stimulation has been used with some success. The second studied the variability in efficacy of different middle ear treatments by quantifying the relevant mechanical and acoustical properties of human ears. We analyzed pressure and velocity measurements from 18 fresh cadaveric human specimens to create a computational impedance model to 1) quantitatively understand sound transmission through the inner ear, and 2) to aid in the development of a RW stimulation device. This model has many applications in the future; like, understanding sound transmission mechanisms. The third developed and tested several RW stimulation prototypes, where we demonstrated that our preliminary Interface Coupler (IC) prototype had improved performance compared to a commercial RW treatment device. The fourth described and tested an improved IC which better fits differences in the anatomy of the RW with an internalized actuator for surgical ease. The improved IC performed well across multiple anatomies, had a linear output with good dynamic range, and produced an equivalent hearing output of at least 90 dB SPL across a wide frequency range. The IC performance was consistent with our impedance model (produced by the second study), exemplifying the many useful applications of the impedance model.