Objective vestibular testing for balance function

Abstract

Objective testing of balance function is crucial for clinical applications that diagnose and monitor the progression of balance disorders. In recent years, a number of new objective testing methods have been developed, including cervical and ocular vestibular evoked myogenic potentials (VEMPs) and the video head impulse test (vHIT). However, the clinical application of these new methods is still being studied. Although methods are often described as objective, in many cases the interpretation of data still relies upon subjective visual interpretation, and so results are highly dependent upon clinical expertise. A statistical analysis of test results can reduce the need for subjective (visual) interpretation. In addition, novel stimulation paradigms have the potential to improve measurement methods by reducing test time or increasing sensitivity to vestibular disorders. The current thesis has two main objectives: 1) to improve objective testing methods through improved stimulation and analysis of responses and 2) to apply the new methods to clinical populations and to compare them with other recently developed objective test approaches.
The key findings of this thesis are:
• Responses can be recorded from the sternocleidomastoid (SCM) muscle with 500 Hz tone-bursts at high stimulation rates, but not in many subjects. The optimal trade-off between recording time and response detection for the majority of subjects appears to be a rate of 10 Hz.
• The onset of the stimulus generates the cVEMP response, so increasing toneburst durations at the same peak level has little effect on the VEMP.
• cVEMP responses can be objectively detected by using statistical approaches, such as a Hoteling’s T2 test, at significantly lower thresholds than those obtained through subjective inspection by experienced audiologists. Statistical testing is a sensitive and efficient method that could replace subjective estimates for detecting the presence of cVEMP responses. This study was the first to objectively estimate the frequency-tuning curve of the saccule using statistical approaches in both healthy subjects and Ménière’s disease (MD) patients.
• Electrocochleography (ECochG) and cVEMP tests failed to pick up some cases that fulfilled American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) criteria for definite MD. However, ECochG was more sensitive to the disease when patients were symptomatic during test recording.
• Although a statistical analysis was not performed for the cochlear implant (CI) study, due to the small sample size, this preliminary study highlighted the importance of evaluating the function of the otolith organs prior to implantation, as the otoliths appear more affected by implantation than the semi-circular canals. However, larger clinical studies would be necessary to confirm these findings.

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