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Published: 2018

Total Pages: 62

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Wideband acoustic immittance (WAI) measures of the middle ear have the potential to increase our ability to detect changes in the middle ear transfer function not seen using traditional tympanometry. In order to use this new tool diagnostically we must first understand its normal clinical variability. The present study aimed to investigate the variability that occurs when wideband acoustic immittance (WAI) is measured clinically within subjects as a function of subject age, as a function of time, and as a function of pressure. A total of thirty-six ears from eighteen subjects were studied (n=18 young adults ears, n=18 older adult ears). Subjects were included in the study if they had negative history of middle ear disease, normal tympanogram at 226 Hz (peak pressure ±50daPA), and an air-bone gap less than 10 dB. Subjects were tested on two days separated by at least a week using a commercial acoustic-immittance system (Interacoustics Titan©). Otoscopy was completed at the beginning of each session to ensure proper probe fit. Following otoscopy, wideband absorbance measurements with a hermetic seal (WBT) were obtained by recording the acoustic response to a click stimulus as a function of frequency and pressure. The wideband clicks were presented at a rate of 21.5/sec and an intensity of 100 dB peSPL (~65 dB nHL) and WAI was measured at 107 frequency data points from 226 to 8,000 Hz. WBT was first measured in the subject's right and left ears and then the probe was reinserted and a second measure was made using the same protocol. Wideband absorbance measures as a function of ambient pressure (WBA) were obtained without pressure next. A hermetically sealed ear canal was not necessary in order to successfully record a WBA measurement from a subject. A measurement was made in the subject's right and left ears, and then the probe was reinserted for a second, identical condition. Both WBT and WBA measures were repeated on a second study session at least one week after the first study session. Wideband absorbance measures for both age groups, under ambient pressure (WBA) were slightly more variable between days than wideband absorbance measure under tympanic peak pressure and with a hermetic seal (WBT). Variability was also seen between tests on the same day after probe reinsertion for both WBA and WBT measurements; however this variability was much smaller than the between-day measurements. Variability remained small in both age groups with slightly greater variability seen in younger adults under both WBT and WBA conditions. Regardless of these factors, essentially all average WAI responses during both test sessions (with the exception of the 6,000 Hz one-third octave interval), fell within the 95% confidence intervals provided by the Titan clinical system. Our results suggest that clinical measures of WAI are most stable when measured at tympanometric peak, and that age may play a role in the amount of variability in WAI over time. Variability over time is small and should not alter clinical decision-making.