It has been widely accepted that as people age the hearing nerve cells degrade. Further this hearing nerve cell degradation was thought to be well estimated from the conventional hearing test procedure known as the pure-tone audiogram.
This age-related hearing loss was thought to be so predictable that the International Standards Organization developed a graph showing the average amount of hearing loss for each decade of life using the conventional pure tone hearing test.
Not only is this conventional test thought to be the standard for diagnosing hearing loss associated with aging but it was also thought to be the test of choice for determining when high levels of noise exposure were permanently damaging hearing.
For decades the conventional pure tone hearing test was used to show whether noise exposure temporarily or permanently damaged hearing nerve cells.
Within the last few years research findings question these assumptions. Specifically it has been demonstrated by Harvard researchers that the conventional hearing test is a very poor estimator of onset of both age-related and noise exposure type hearing loss.
Further the long-held belief that the conventional pure-tone audiogram could separate temporary from permanent hearing damage has been disproven.
Rather than relying on conventional hearing test procedures the group from Harvard examined the wiring that connects to the hearing nerve cells. These axons and the terminals connected to the hearing nerve cells have been shown to be much more sensitive to the onset of both types of hearing loss. Specifically both the aging ear and the ear exposed to high levels of noise show major damage to these axons and their terminals long before any hearing loss shows up with conventional hearing testing techniques.
Further in the early stages of axon damage no hearing loss is apparent through conventional technique. Unfortunately studies have shown that once the axons disappear the hearing nerve cells die within a decade.
The implications of these findings are considerable. First use of the pure-tone audiogram to determine whether a given noise level has damaged hearing is inappropriate. This is true both for industrial noise exposure as well as the noise exposure sustained by veterans in the line of duty.
Further, much damage can be done through the process of aging before the conventional hearing test shows this damage has occurred.
It has now been shown that degraded speech tests and a procedure known as ultra-audiometric testing are much more revealing of the damage that occurs due to noise exposure and aging. Further the levels of noise thought to be safe by the Occupational Safety and Health Administration are too high and hearing protection should be required much sooner than previously thought.
This topic will be discussed in greater detail on August 11th, 2016 from 3:30 to 5 PM in Conference Room B at Corvallis Good Samaritan Hospital. The public is invited. There is no charge and no reservations are needed.