Laser Doppler vibrometry (LDV) is an emerging technology for assessing middle ear (ME) function that detects the sound-induced velocity (Vu) of one of the ME bones, the malleus, over a wide frequency range (300 to 6000 Hz) using a reflected laser beam. The PI seeks to develop LDV measures as a new research area in line with his previous work in the assessment of ME function using wideband acoustic immittance (WAI) measurements. Because LDV measures the movement of one of the ossicles, it is inherently sensitive to ossicular chain disorders such as otosclerosis, and is thus a potentially useful diagnostic tool. LDV obtained at ambient pressure in the ear canal has been shown to result in similar diagnostic sensitivity to WAI, but has wide variability. The diagnostic capability of LDV may be enhanced by making measurements at tympanometric peak pressure (TPP) rather than ambient pressure to control for the effects of varying middle- ear pressure from test to retest and across subjects. This ME pressure related variability may mask underlying ME disorders. Moreover, a comparison of Vu at TPP with tympanometric tail pressures (e.g. 200 daPa) may provide additional information about the ME status that previously has not been measured. This will be the first study to evaluate the use of tympanometric (varying ear canal pressure) LDV measures for the assessment of ME function.
Aim 1 is to make the first repeated measures of Vu at TPP and tympanometric tail pressures in control subjects with normal ME function using a custom ear speculum developed at the VA National Center for Rehabilitative Auditory Research (NCRAR). These test-retest differences will be compared with measurements obtained at ambient pressure by fitting a hierarchical Gaussian process regression model to these data, as well as comparing the data to published test-retest differences for Vu at ambient pressure.
Aim 2, using the data from Aim 1, will establish reference limits as a function of frequency for ambient pressure, TPP, 100 daPa, and 200 daPa, and for tympanometric peak-to-tail differences for 100 daPa and 200 daPa.
In Aim 3 the reference limits established in Aim 2 will be applied to the Vu data obtained from 10 subjects with a diagnosis of otosclerosis for ambient pressure and pressurized measures. A Bayesian hierarchical regression model will be used to compare mean differences in Vu between the control group and the otosclerosis group at each of the 9 stimulus frequencies in each test condition. Subjects will be recruited using the NCRAR data repository, through approved flyers posted in the VA Portland Health Care System (VAPORHCS) and handouts provided to patients from audiologists or otolaryngologists in VAPORHCS clinics. Enrollment in the study is for two study visits for both control subjects and those with otosclerosis: The first visit involves hearing evaluation and tympanometry as well as measurements of LDV for both ears at ambient pressure, tympanometric peak pressure determined by 226 Hz tympanometry, and for tympanometric tail pressures at 100 and 200 daPa. At the second study visit approximately one month later all tests will be repeated. Based on preliminary data collection, we anticipate that each visit will last approximately 2 hours. Subjects will be tested in a sound-treated booth for all tests. A clinical audiometer will be used for hearing tests followed by tympanometry using a clinical tympanometer. LDV measurements will be completed with a Polytec OFV 534 laser vibrometer. Two research audiologists are required for each measurement: one to position the speculum and manipulate the laser, and the second to assist in computer data acquisition. Air pressure will be varied using the pressure pump from the tympanometer connected to the custom speculum with standard tubing to make measurements at TPP and 100 and 200 daPa. The study outcomes will inform the specific aims for a VA Merit Review or NIH R01 study to compare ambient and tympanometric LDV in the assessment of various ME disorders with the long- term goal of moving to a clinical trial of this technology for Veterans with ME disorders.
The long-term goal of the proposed research is to improve the diagnostic assessment of middle ear (ME) disorders in Veterans with non-invasive measures to help direct appropriate treatment. Over 85,000 Veterans per year present with hearing loss due to the ME. It is currently very difficult to diagnose hearing loss due to the chain of tiny bones in the ME in cases where the eardrum in intact. This study seeks to improve upon a technique for diagnosing this problem that uses a laser to measure the vibration of the ME bones. This technique is called laser Doppler vibrometry (LDV). We have developed a system to perform LDV while adjusting for any ME pressure in an individual's ear. This promises to greatly reduce test variability and improve the diagnosis of ME disorders. Results from this study will be used to support a VA Merit Review grant to evaluate the pressurized LDV technique in Veterans with various ME disorders.
