According to this study, a widespread occurrence of middle-ear disease and the difficulty of accurately identifying the cause of conductive hearing loss, non-invasive, cost-effective diagnostic tools that reliably distinguish among middle-ear pathologies would be valuable. It supports in better selection of cases for surgery, surgical preparation, patient counselling, as well as help prevent unnecessary surgeries.
This study deals with comparisons between different objective measurements of middle-ear function in a “normal” population, where our definition of “normal” is strict. While our restriction to ears with normal clinical history, audiometry and tympanometry are common to most studies, a significant difference is that we require both ears to meet the normal criteria for any subject to be counted as normal.
This restriction was placed because of our informal and unpublished observations that patients with unilateral conductive hearing loss due to otosclerosis, who exhibit low-normal middle-ear function (as determined by umbo-velocity measurements) in the affected ear, often show similar low-normal middle-ear function in the contralateral ear despite having normal hearing thresholds.
One interpretation of this observation is that the contralateral ear is affected by sub-clinical middle-ear disease and is not strictly normal. Our requirement that both ears of a subject meet normal criteria before either ear is considered normal, limits the possibility that subclinical pathology is included in the normal population.
As discussed in the results, our selection of normal subjects based on binaural criteria allowed us to check for left-right differences in power reflectance. We conducted paired-tests investigating the significance of left-right differences in power reflectance at each of 9 logarithmically spaced frequencies. The differences in reflectance between the left and right ear approached 15% of the grouped mean at 2 and 8 kHz, but were only significantly different from zero (p value < 0.05) at 0.3 kHz.
They conclude, their was a tendency for the right ear to have larger reflectance values at frequencies below 1 kHz. Whether this tendency is significant bears further investigation. They also observed small differences between left and right ears in |ECR|2.
Small but significant differences between umbo velocity measurements in the left and right ears of individuals have also been reported, while documented significant correlations between umbo velocity measurements in left and right ears. If these differences are indeed real, they may indicate small differences in the dimensions of the left and right ears or small differences in the mechanical parameters that govern middle-ear function.