Operating Instructions
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The improved operation in noise with the new algorithm was so substantial that we conducted a
complete replica of our original validation tests in "fully impaired ear" cavities and were able to verify
that no increase in false negatives (false passes) was introduced. Under no test conditions was any such
degradation uncovered.
The artifact rejection can only reject the noisiest samples in a measurement period. If the ambient noise
level rises too high (and/or the eartip seal is poor), then all samples will be noisy and accurate
measurements will be impossible, in which ca
se the test result will indicate “noisy.”
Occasional claims of extraordinarily low probabilities of missing an ear with hearing loss appear to be
based on poor statistics. As discussed by Gorga (1999), since the incidence of significant hearing loss is
roughly 2 per 1000, verifying a 99.7% accuracy would require testing hundreds of thousands of babies
with a given system. Thus to demonstrate that only 3 babies out of 1000 with hearing loss were missed
would require follow-up testing on 500,000 babies. To our knowledge, no one has performed such
tests to date.
Pass/Refer Criteria for Tympanometry:
Tympanometry measures sound reflection from the tympanic membrane, while air pressure is
varied in the ear canal. The tympanogram is a quick measurement providing a snapshot of the
overall status of the middle ear. The primary features of a tympanogram are the ear canal
volume, peak amplitude of the tympanogram (compliance), pressure point of the peak
(pressure), width of the tympanogram (gradient), and overall shape of the curve (Hall &
Mueller, 1997). Reported normative values for these measurements vary considerably
depending on subject population, methodology, and criteria for the study. For example, the
reported limits for pressure can vary by 50 dapa and compliance limits can vary by 0.30 ml
depending on the study cited (Gelfand, 2001; Hall & Mueller, 1997). Additionally, the range of
values found with various pathologies overlaps the range found with normal ears (Gelfand,
2001; Harris et al., 2005).
It is for these reasons that tympanograms are not used in isolation to diagnose or screen for
pathologies of the middle ear system, but rather are considered with additional audiological
measures, such as Otoacoustic Emissions and Acoustic Reflex measurements as part of a
diagnostic or screening battery.
Pass/Refer Criteria for Acoustic Reflex:
An acoustic reflex, or contraction of the Stapedius muscle, occurs under normal conditions
when a sufficiently intense sound is presented to the auditory pathway. This contraction of the
muscle causes a stiffening of the ossicular chain which changes the compliance of the middle
ear system. For best results, this reflex measurement is automatically conducted at the air
pressure value where the compliance peak occurred during the tympanometric test. Stimulus
tones of varying intensities at 500, 1000, 2000 or 4000 Hz are presented as short bursts. If a
change in compliance greater than 0.05 ml is detected, a reflex is considered present.
Note: The box shown on the tympanogram indicates the normative area where the peak of the
tympanogram is expected under normal conditions. The Pass/Refer result is based on presence or
absence of the peak within the bounding box. The limits selected are intended to separate normal
ears from significantly abnormal ears across most populations.
Users with the goal of detecting mild conditions of the middle ear should ensure that appropriate age
related norms are used in setting Pass/Refer criteria.
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