Audiology in Brief Shape matters in low-frequency hearing. A link between the cochlea’s curvature and the low-frequency hearing limit has been established in more than a dozen different mammals, according to a study published recently online in the Proceedings of the National Academy of Sciences. “It turns out that it is the ... News in Brief
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News in Brief  |   October 01, 2008
Audiology in Brief
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Hearing Disorders / News in Brief
News in Brief   |   October 01, 2008
Audiology in Brief
The ASHA Leader, October 2008, Vol. 13, 5. doi:10.1044/leader.NIB.13142008.5
The ASHA Leader, October 2008, Vol. 13, 5. doi:10.1044/leader.NIB.13142008.5
Hearing Takes Shape
Shape matters in low-frequency hearing. A link between the cochlea’s curvature and the low-frequency hearing limit has been established in more than a dozen different mammals, according to a study published recently online in the Proceedings of the National Academy of Sciences.
“It turns out that it is the curvature of the cochlea, not its size, that is highly correlated to the low-frequency hearing limit,” said Daphne Manoussaki, assistant professor of mathematics at Vanderbilt University, who headed the new study with Richard S. Chadwick, a section chief at the National Institute on Deafness and Other Communication Disorders at the National Institutes of Health.
Manoussaki’s calculations predicted that the spiral shape of the cochlea causes the energy in the low-frequency waves to accumulate against the outside edge of the cochlea. This uneven energy distribution, in turn, causes the basilar membrane to move more toward the outer wall of the cochlea, which enhances the bending of the stereocilia. The enhancement is strongest at the apex of the cochlea’s spiral, where the lowest frequencies are detected. Manoussaki and her colleagues calculated that the increase in the sound-pressure level can be as much as 20 dB.
The researchers analyzed high-resolution CT scans of the cochlea of different species of land and marine mammals and found that the low-frequency hearing limits of species ranging from mice to cats to cows to whales varied in step with the ratio of the radii of curvatures at their cochlea’s base to that of its apex, expressed as a single, simple measure of curvature change. This measure varies from about two to nine: the larger the measure, the lower the frequencies that the animal can hear.
Manoussaki explained that as the ratio increases, the spiral is wound more tightly and more of the low-frequency sound wave energy is forced against the cochlea’s walls. To read the open-access article, visit PNAS Online.
Cerumen Impaction Guidelines
The American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF) issued the first comprehensive clinical guidelines to help health care practitioners identify patients with cerumen impaction. The guidelines are not meant to be the sole source of guidance, but are designed to provide an evidence-based framework for decision-making strategies. Created by a multidisciplinary panel of clinicians from otolaryngology, audiology, family medicine, geriatrics, internal medicine, nursing, and pediatrics, the guidelines are intended for all clinicians who are likely to diagnose and manage patients with cerumen impaction.
The new guidelines emphasize that clinicians should examine patients with hearing aids for cerumen impaction because it may cause feedback, reduce sound intensity, or damage the hearing aid. Individuals at high risk for cerumen impaction, such as hearing aid users, should consider seeing a clinician every six to 12 months for routine cleaning. Appropriate options for cerumen impaction include cerumenolytic (wax-dissolving) agents, irrigation or ear syringing, and manual removal with special instruments or a suction device. The guidelines caution that inappropriate or harmful interventions include cotton-tipped swabs, oral jet irrigators, and ear candling. To review the guidelines, view the article online [PDF].
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October 2008
Volume 13, Issue 14