AVAA Presents Update on Landmark Study During 5th Annual Meeting
Washington, DCDuring their fifth annual meeting March 30, the Association of VA Audiologists (AVAA) presented follow-up findings from their landmark study, Efficacy of 3 Commonly Used Hearing Aid Circuits, A Crossover Trial (Larson et al., JAMA, Oct 11, 2000, V284, No. 14: 1806-13). The updated studyalso conducted by the Department of Veterans Affairs (VA) and the National Institute on Deafness and Other Communication Disorders (NIDCD)found that most of the findings from the original clinical trial (1996-1998) held true 6-7 years later. Importantly, the study suggests that long-term benefits exist for hearing aid use, the reliability of hearing instruments over time is high, and the aids are deemed to be very useful by the wearers.
Revisiting a Young Classic Paper
While the information in what has become known in the hearing care field as the VA Study may by now be old news for those who have seen presentations on the material, the fact that it appeared in the Journal of the American Medical Association is reason enough for all hearing care professional to make sure that every family/general practitioner in the US receives a copy of it. Essentially, the study provides some of the most convincing support for how hearing instruments improve communicative ability in both quiet and noisy environments, and why they represent an excellent solution for hearing-impaired people. Additionally, the study is one of the few large-scale, multi-site, double-blinded studies (ie, both the subjects and the dispensing professionals were unaware what specific hearing instrument technologies they were using) in hearing care literature.
The original study involved 360 subjects with bilateral sensorineural hearing losses in eight VA hospitals across the US from May 1996 to February 1998. Three hearing instrument technologies (peak clipping, compression limiting, and wide dynamic range compression, in identical shells) were provided to the subjects, so that all subjects used each instrument technology type for 3 months. Following both the initial fitting and the 3-month trial, each subject was tested for speech recognition (using the NU-6 and the CST at a variety of presentation levels and SNRs using multi-talker babble), sound quality (loudness, noise interference, and overall liking) and subjective benefit (PHAB). They were also asked to rank each instrument in order of preference.
The results of the study showed that all three hearing instrument technologies substantially improved speech recognition on the NU-6 by an average of 29% (absolute score improvement), even though all of the aids provided reduced benefit scores on the CST as the signal-to-noise ratio deteriorated. The speech recognition improvement in noise ranged from 10-30% over the unaided condition, with better results for soft and conversational loudness levels.
As would be expected, some of the test results suggested that the compression limiting and WDRC instruments outperformed the peak clipping instrument in word recognition, loudness, overall liking, aversiveness of sounds, and distortion. For example, the WDRC instrument was rated as having the most comfortable loudness compared to the other two instruments; likewise, the compression limiting instrument was rated ahead of the peak clipping instrument in comfort. However, the peak clipping instrument scored better than WDRC in noise interference.
In overall ranking, 41.6% of the subjects chose the compression limiting instrument, followed by the WDRC (29.8%), and the peak clipping (28.6%) instruments. Additionally, the compression limiting instrument was ranked third by the lowest percentage of subjects (25.4% vs. 36.2% for peak clipping and 38.4% for WDRC).
What is most important to recognize about the study is that all three instruments provided substantial speech intelligibility and benefit over unaided conditions and demonstrably reduced the subjects communication problemseven in the presence of background noise.
New Long-Term Findings
The original VA Study provided excellent proof that hearing instruments worked in, at least, the short term. The purpose of the follow up study, as detailed by Gene W. Bratt, PhD, chair of the study and an audiologist at the VA Medical Center in Nashville, was to determine 1) if the short-term benefits noted in the original study had, indeed, continued; 2) current user and non-user patterns and reasons for changes in usage; and 3) if there were any differences between the circuits.
The new findings present excellent news: the majority of original study subjects who wear their hearing aids continue to benefit from the devicesand a stunning 83% of the original subjects who participated in the follow-up study were still wearing hearing aids. Additionally:
Barbara Peek, PhD, showed that the performance of the original aids remained very stable after 5-6 years, and newly purchased hearing aids have very similar electroacoustic performance characteristics as the older aids. Additionally, Peeks group found that most users prefer the lower NAL-RP IG levels. The mean real-ear saturation responses (RESR) of the aids were similar to those obtained in the original study, suggesting that the aids retained original amplification levels that are both safe and comfortable for users.
Reasons for changes in amplification, as well as usage patterns, were covered by Charles Martinez, AuD. Using HASQ and SADL tests, he showed that 56% of the study subjects used their hearing instruments more than 8 hours per day.
Bratt showed that hearing aids provided benefit both in quiet and in background noise. Although performance was slightly poorer in the follow-up study, this was attributed to a 10 dB degradation in hearing over the 6-7 years. Hearing aid benefit was greater at lower presentation levels than higher presentation levels. Additionally, non-users tended to perform better in unaided conditions (ie, they had less trouble perceiving speech) than current users.
The study is expected to be published in a future issue of an audiology professional journal, if not a major medical publication.