Posted Feburary 2, 2018

Timothy Walilko, Ph.D., Applied Research Associates, Inc., Albuquerque, New Mexico

Auditory injury caused by shockwaves emitted by explosive devices and high energy impact is the leading cause of medical referral for military Veterans of Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF) (Helfer 2005). Short-term impacts to Soldiers following blast exposure include disorientation and temporary loss of hearing, both of which severely reduce combat effectiveness and survivability. Degraded performance is a long-term impact caused by impaired interpersonal communication, diminished sensory awareness, and potential disqualification from duty, affecting not only the individual, but also fellow Service Members. While hearing protection devices (HPDs) can be effective for mitigating noise and blast injury, they typically cause significant sensory deprivation and decreased ability to communicate, thereby reducing compliance among both military and public occupations. The Auditory Hazard Assessment Algorithm in Humans (AHAAH) is a mathematical model of the human auditory system that is used to assess the potential for various noises (e.g., machinery, weapons, and blast events) to cause hearing injury. The AHAAH model also has the potential to be used to evaluate the effectiveness of HPDs, albeit with significant limitations. Dr. Walilko and his team at Applied Research Associates are addressing these limitations by employing new technologies, including: multidimensional laser doppler vibrometry (LDV) and fiber optic pressure gauges (FISO) - capable of measuring vibration of the bones in the middle ear and intra-cochlear pressure, respectively. They are also using immunohistochemical and electrophysiological techniques that allow examination of auditory injury at the cellular level. Their goals are to develop a neuro-functional understanding of acoustic injury, an animal model that correlates to human auditory mechanisms and physiological responses to noise and blast events, and a more robust system for evaluating HPDs across a broad range of intensities and frequencies observed in real-world exposures.

The Joint Program Committee-5/Military Operational Research Program funded and Congressionally Directed Medical Research Programs (CDMRP) managed Dr. Walilko through the Injury Prevention, Physiological and Environmental Health Award offered by the CDMRP's Defense Medical Research and Development Program. During the first two phases of this study, the research team developed a blast wave emulator used to excite the tympanic membrane, bones of the middle ear, and cochlea such that the motion of the membrane and bones in post-mortem human surrogates (PMHS) can be quantified using LDV. Similar measurements will continue to be analyzed during Phase 3 along with measurements of the response of the auditory nerve in animal surrogates to various noise hazards and blast pressures from a variety of sources relevant to the military. The team began converting the AHAAH model from the Pascal programming language to the more current and widely used Matlab program in the first year of this four-year study. They also developed a protocol for implanting FISOs within the middle ear and cochlea that provided a new and innovative sensing modality for current and future auditory research. In Year 2, the team began implementing improvements to the model's hearing protection module, integrating their data into new parameters and algorithms for the model that would enhance the predictive performance of HPDs under various auditory hazard conditions observed in real-world combat and military training environments. Measurements of the auditory response in animals will be conducted in Year 3 to extrapolate to the AHAAH model to predict auditory injury, correlating human and animal auditory mechanisms and physiological responses to noise and blast events. Year 4 will include final parametrization, calibration, and conversion of the AHAAH model from Pascal to Matlab such that the technology can be transferred and shared among the scientific community.

It is estimated that 71% of Soldiers who returned from OEF and OIF were exposed to loud noises and nearly 16% report symptoms of tinnitus (Helfer 2005). Likewise, civilian populations also experience hearing loss as a result of occupational and recreational noise exposure with an estimated cost to society of approximately $300,000 over the life of an individual (Mohr, 2000). By improving and extending our understanding of auditory injury under real-world conditions, Dr. Walilko's research has advanced the development of new technologies that can prevent and mitigate injury to the auditory system. This research also improves techniques designed to assess the effectiveness of HPDs, thereby paving the way for new and improved auditory protection systems. Dr. Walilko and his team have already published two peer-reviewed scientific articles and presented their preliminary results at three professional meetings. Several more articles and presentations are forthcoming that will facilitate future research seeking to assess the effectiveness of HPD systems and prevent and mitigate auditory injury.

References:

Helfer TM, Jordan NN, Lee RB, et al. Postdeployment hearing loss in U.S. Army solidiers seen at audiology clinics from April 1, 2003, through March 31, 2004. Am J Audiol. 2005; 14:161-168.

Mohr PE, Feldman JJ, Dunbar JL, et al. The societal costs of severe to profound hearing loss in the United States. Int J Technol Assess Health Care. 2000. 16(4):1120-1135.

Publications:

Greene NT, Jenkins HA, Tollin DJ, et al. Stapes displacement and intracochlear pressure in response to very high level, low frequency sounds. Hear Res; 2017 Feb 9. 348:16-30.

Maxwell AK, Banakis-Hartl RM, Greene NT, et al. Semicircular canal pressure changes during high-intensity acoustic stimulation. Otol Neurotol. 2017 Aug; 38(7):1043-1051.

Link:

Public and Technical Abstracts: Improvement and Extension of Auditory Hazard Models

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