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Corrected some misinformation on this page regarding the pervasiveness of middle ear muscle contraction and edited the AHAAH model claims. |
m Removed the self-promoting and unsubstantiated claim about accuracy with double protection. There have not been any human studies of double protection against which the AHAAH model and its exposure predictions can be verified. The Nakashima report that the page cited, specifically recommended against using AHAAH in its present form. It was published after MIL-STD 1474E (April 15, 2015) was made available. Changed the indication of which agencies have recommended the use of AHAAH. |
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The AHAAH model incorporates two unique features, the activation of the middle ear muscle contraction (MEMC) and the limitation of the motion of the stapes via the [[Annular ligament of stapes|annular ligament]]. The bones of the middle ear are supported by ligaments and muscles in the middle ear cavity. The [[Tensor tympani|tensor tympani]] muscle attaches to the malleus bone. The [[Stapedius|stapedius]] muscle attaches to the top of the [[Stapes|stapes]]. When these muscles contract, the transmisdion of sound from the ear canal to the cochlea is reduced. The AHAAH model analyzes the response of the ear in two modes: warned and unwarned. In the warned mode, the muscles are assumed to be already contracted. In the unwarned mode, the muscles are contracted after a loud sound exceeds a threshold of about 134 dB peak SPL. Several studies conducted between 2014 and 2020 have examined the prevalence and reliability of the MEMC. According to a nationally representative survey of more than 15,000 persons, the prevalence of the acoustic reflex measured in persons aged 18 to 30 was less than 90%.<ref>{{cite journal |last1=Flamme |first1=Gregory A. |last2=Deiters |first2=Kristy K. |last3=Tasko |first3=Stephen M. |last4=Ahroon |first4=William A. |title=Acoustic reflexes are common but not pervasive: evidence from the National Health and Nutrition Examination Survey, 1999–2012 |journal=International Journal of Audiology |date=21 November 2016 |volume=56 |issue=sup1 |pages=52–62 |doi=10.1080/14992027.2016.1257164}}</ref> A follow-on study that carefully assessed 285 persons with normal hearing concluded that "acoustic reflexes are not pervasive and should not be included in damage risk criteria and health assessments for impulsive noise."<ref>{{cite journal |last1=McGregor |first1=Kara D. |last2=Flamme |first2=Gregory A. |last3=Tasko |first3=Stephen M. |last4=Deiters |first4=Kristy K. |last5=Ahroon |first5=William A. |last6=Themann |first6=Christa L. |last7=Murphy |first7=William J. |title=Acoustic reflexes are common but not pervasive: evidence using a diagnostic middle ear analyser |journal=International Journal of Audiology |date=19 December 2017 |volume=57 |issue=sup1 |pages=S42–S50 |doi=10.1080/14992027.2017.1416189}}</ref> The anticipatory contraction integral to the warned response is not reliable in persons with normal hearing.<ref name=Deiters>{{cite journal |last1=Deiters |first1=Kristy K. |last2=Flamme |first2=Gregory A. |last3=Tasko |first3=Stephen M. |last4=Murphy |first4=William J. |last5=Greene |first5=Nathaniel T. |last6=Jones |first6=Heath G. |last7=Ahroon |first7=William A. |title=Generalizability of clinically measured acoustic reflexes to brief sounds |journal=The Journal of the Acoustical Society of America |date=November 2019 |volume=146 |issue=5 |pages=3993–4006 |doi=10.1121/1.5132705}}</ref><ref name=Jones>{{cite journal |last1=Jones |first1=Heath G. |last2=Greene |first2=Nathaniel T. |last3=Ahroon |first3=William A. |title=Human middle-ear muscles rarely contract in anticipation of acoustic impulses: Implications for hearing risk assessments |journal=Hearing Research |date=July 2019 |volume=378 |pages=53–62 |doi=10.1016/j.heares.2018.11.006}}</ref>
As the MIL-STD-1474 has evolved, technology and methods have improved the AHAAH model’s accuracy.
== References ==
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