The following presentations were given by AFAA members at the 1996 MASC in Virginia Beach, VA. These presentations have continued to enhance our members knowledge in many ways. Those who present papers at future short courses receive priority funding for course attendance.
Management of Distortion Product Otoacoustic Emissions Based on Advanced Fuzzy Logic Filtering Techniques
LtCol John R. Allen, Jun Zhou, Ph.D., Harold G. Longbatham, Ph.D., Hermal N. Kothari, M.S., Anantrachai Kaewlium, B.S
Distortion Product Otoacoustic Emission (DPOAE) measures are gaining wider acceptance and use as a routine measure of cochlear outer hair cell integrity. The typical approach to measuring DPOAE includes the use of classical synchronous averaging. This is a linear operation which has serious limitations in the suspension of certain types of noise. As such, it is explicitly assumed that noise and other artifacts are independently and evenly distributed in the measurement equipment and biological system, and impulse noise does not exist. This assumption holds only for limited situations and therefore, it limits the reliability of the averaging operation. We sought to apply fuzzy modeling techniques to better control the effects of ambient noise, both biological and environmental. A modified version of the software for the Virtual model 330 DPOAE system was employed. Raw DPOAE data was obtained and fuzzy logic procedures were applied. Results showed that this approach can extract DPOAE responses from noisy data more efficiently and consistently at all the frequencies that the current technique.
Comparison Between Blind and Visual Electrode Placements in Tympanic Electrocochleography
Capt William J. Lopez II
82nd MDG/SGOSLA
Sheppard AFB, TX
Electrocochleography (ECochG) continues to be a useful tool in helping identify Wave I of the auditory brainstem response (ABR), in interoperative monitoring, and in diagnosis and monitoring of Meniere’s Disease. Although transtympanic (TT) recording approaches to ECochG produces larger and more sensitive responses, non-invasive, extratympanic (ET) methodology has proven effective for routine clinical applications, especially when the tympanic membrane (TM) is used as the primary recording site.
Ferraro and Ferguson (1989 and 1990) have modified the Stypulkowski and Staller (1987) TM electrode and have referred to it as the tymptrode. Their method of tymptrode placement, utilizing an immittance tip, has several advantages. However, a disadvantage is that the electrode is placed ÒblindlyÓ with reliance upon the patient to confirm contact with the TM. Patient confirmation may not always be accurate. This can delay/prolong the EcochG examination, result in poor recordings, and contribute to within and between subject variability. These problems could possibly be overcome if contact with the TM was visually confirmed by the examiner prior to recording.
This study was conducted to compare blind and visual approaches to placement in normal hearing subjects to help identify the method most appropriate for clinical TM-ECochG.
Application of Advanced Signal Processing Filtering Techniques to Auditory Brainstem Response Measures
Capt Cynthia A. Sabin, LtCol John R. Allen, Edward J. Engelken, Ph.D., Harold Longbatham, Ph.D., Bennie Pierce, M.S., Ping Yan, M.S
Auditory Brainstem Response (ABR) measures have been used for many years to estimate auditory threshold and assess the integrity of the peripheral auditory system. Previous clinical work has been compromised for various reasons. Among others, the simplistic technique of cross-averaging has resulted in protracted testing sessions, as well as poor amplitude resolution. We sought to address three major drawbacks of the cross-averaging method. First, we approached the susceptibility of this technique to impulsive noise and DC (baseline) drift. Second, we attempted to reduce the processing time (i.e. typically 2000 sweeps). Finally, we addressed the problems associated with highly variable wave amplitudes. Results demonstrated consistent amplitude and latency measurements for the same person. At the same time, the number of averaged responses has been reduced from 2000 sweeps to 300 sweeps while retaining approximately the same quality of the wave form and attenuating the noise level. Clinical implications and future directions are discussed.
The Effects of Linear Acceleration on Distortion Product Otoacoustic Emissions in Human Ears
Maj Theresa Schulz, Ph.D., Capt Robert E. Johnson, LtCol John R. Allen, Ph.D., Maj Douglas A. Liening, M.D., Ann F. Bell, M.D.
The effect of high levels of linear acceleration (G) on the cochlea has never been studied prospectively. Twenty-two healthy volunteers underwent exposure to up to 9G in a military aviation training centrifuge. Prior to exposure they were screened for cochleovestibular disorders and underwent typanometry, audiometry and distortion product otoacoustic emissions (DPOAE) testing. Immediately after exposure, they underwent serial testing of each parameters until they returned to baseline. There was no significant change in tympanometry in any subject. Audiometry revealed a temporary threshold shift (TTS) of 30dB at 6kHz in one ear of a single subject. This was not accompanied by a complete loss of DPOAE at the same frequency. DPOAE did not return to baseline at 2 weeks even though the audiogram had reverted to baseline by 8 days. Four other ears displayed significant losses of emissions at single frequencies without an accompanying change on the audiogram. This study demonstrates that accelerative stress can cause transient injury to the cochlea. The mechanism of injury due to acceleration is probably ischemia, although a purely mechanical effect on the outer hair cells cannot be precluded. These data also reinforce a growing body of evidence that demonstrates the greater sensitivity of DPOAE over psychoacoustic testing in detecting early subclinical cochlear damage.