Electrocochleographic Recordings from the Eardrum: Variations and Effects of Electrode Location in Normal Subjects

Objectives: The primary goals of this study are to observe the degree of variation of the tymptrode position on the TM and the marker's area size among a population of adult subjects with normal hearing, and to investigate the effects of these variations on the ECochG outcomes. Methods: Normative values were established for ECochG parameters. Tymptrode locations on the TM were detected by observing the gel marker in 50 TM images. 47 ECochGms were recorded for 18 normal hearing subjects. 14 subjects were tested three times and 4 subjects were tested two times. Two parameters were used to measure the location of the tymptrode on the TM: the angle and the length. First, a mixed model was used to investigate if the tymptrode location on the TM and the marker's area size were significantly different every time the same subject was re- tested. Secondly, a mixed regression model was used to investigate if the variations of the tymptrode location on the TM affect the ECochG outcomes when all other parameters were held constant. Results: Results revealed that the angle of the tymptrode location on the TM was significantly different across all the measurements every time the same subject was tested. A mixed regression model results revealed no significant effect of the electrode location or the marker's area size on the SP/AP amplitude ratio. However, there was a significant effect of the angle of the marker on the SP/AP area ratio. Most important, clinically there were no important effects of the tymptrode location variations on the ECochG outcomes. Conclusion: Variations of the tymptrode location on the TM had no clinically significant effects on the outcome of an ECochG exam in normally hearing subjects