An investigation of cochlear dynamics in surgical and implanation processes

Abstract

The aim of this research is to improve the understanding of the impact on the cochlear dynamics corresponding to surgical tools, processes and hearing implants such that these can be designed more appropriately in the future. The results suggest that enhanced performance of implants can be achieved by optimisation of the location with respect to the cochlea and have shown that robotic surgical tools used to enable precise, simplified processes can reduce harm and offer other benefits. With an ageing population, and where exposure to noise on daily basis is increased rather than industrial settings, at least two factors of age and noise, will contribute to a greater incidence of hearing loss in the population in the future. In the research a mathematical model of the passive cochlea was produced to increase understanding of the sensitivity and behaviour of the fluid, structure and pressure transients within the cochlea. The investigation has been complemented by an innovative experimental technique developed to evaluate the dynamics in the cochlear fluids while maintaining the integrity of the cochlear structure. This technique builds on the success of the state-of-the-art surgical robotic micro-drill. The micro-drill enables removal of bone tissue to prepare a consistent aperture onto the endosteal membrane within the cochlea. This is known as preparing a ‘Third window’. In this technique the motion of the exposed endosteal membrane is treated as the diaphragm element of a pressure transducer and is measured using a Micro- Scanning Laser Vibrometer operating through a microscope. There are two principal outcomes of the research: First, the approach has enabled disturbances in the cochlea to be contrasted for different surgical techniques, which it is expected to allude preferential methods in future surgery in otology. In particular it was shown that when using the robotic micro-drill to create a cochleostomy that the disturbance amplitude reduces to 1% of that experienced when using conventional drilling. Secondly, an empirically derived frequency map of the cochlea has been produced to understand how the location of implants affects maximum power transmission over the required frequency band. This has also shown the feasibility of exciting the cochlea at a third window in order to amplify cochlear response.