Although a study of noise-induced hearing loss in the military was made after World War I, no action was taken. Consequently in World War II, the lessons on protecting military personnel’s hearing from the modern battlefield’s noise were relearned.
Because the military environment constitutes one of the most noise-hazardous occupational settings, the U.S. Army has developed a hearing conservation program. This program reduced the hearing loss of Army personnel with more than 10 years service in combat arms, such as infantry, armor or artillery, by more than 35 percent. However, noise-induced hearing loss, especially military noise hazards, remain important and these hazards are increasingly prevalent problems in training and especially in the theater of operations.
For military personnel, hearing damage from acoustic trauma accounts for approximately 47 percent of all wounded-in-action evacuations of Operation Iraqi Freedom and Operation Enduring Freedom, and hearing damage is the fourth leading reason for medical referrals when returning from deployment. These injuries result in a rise in costly U.S. Department of Veteran Affairs’ disability expenditures, reduced competitiveness in the post-service job market, and diminished quality of life. From the military’s perspective, the main concern is these hearing injuries hamper combat readiness. Furthermore, well-trained and motivated service members are lost to hearing damage.
Hearing is the only continuous awareness system that alerts a soldier to a 360-degree panorama of the individual’s environment. Hearing becomes especially important in the dark when vision is reduced. Casualties have been attributed to the loss of hearing acuity in combat situations.
Hearing loss in the military is on the rise again for a variety of reasons. In fact, disability claims for hearing loss for Marine Corps veterans have risen dramatically in the last three years, and estimates by the U.S. Army Center for Health Promotion and Preventative Medicine predict that the hearing loss among personnel with more than 10 years of service will increase 25 percent – levels approaching the pre-hearing conservation era. The increase may be attributed to the advent during the past decade of several armed conflicts involving U.S. personnel; the development of noisier weapons systems; changes in military tactics including the use of roadside explosive devices and more urban locations; challenges in acquiring and deploying hearing protection; and shortages of personnel who conduct military-wide hearing conservation programs. It would seem that the hearing loss problem could be solved through adequate distribution and use of effective hearing protection devices. However, as the military has learned through decades of study, the problem and its solution are not so simple.
Combat noise, especially that of military equipment, often exceeds the protection provided by doubling hearing protection with earplugs and muffs. Take for example, a Navy launch crew standing only 50 feet away from an F-35 Joint Strike Fighter jet launched from an aircraft carrier. Despite doubling the hearing protection, the crew will exceed, in only one launch, the total daily noise maximum established by the Occupational Safety and Health Administration. During operations these aircraft are often launched and recovered every several minutes around the clock. In addition, noise levels in the military environment are so high (some shoulder-fired weapons generate an incredible 180 decibels of impulse noise) that the damaging noise bypasses hearing protection and traverses directly through the skull, thus damaging the cochlea.
Another important issue in combat is the need to hear. However, many types of hearing protection devices also attenuate important environmental cues and spoken commands, one reason why these devices are not used in combat. But without hearing protection, personnel leave themselves exposed to sudden and surprise dangers such as a blast occurring. Finally, some toxins, such as carbon monoxide and jet fuel fumes, present in a military environment, when combined with loud noises, accentuate damage to the cochlea, thus causing hearing loss. Unfortunately, existing hearing devices do not protect against these ototoxins.
For many reasons the U.S. Department of Defense (DoD) has spent millions of dollars on research and development during this past decade to understand the mechanisms of hearing loss caused by acoustic trauma and to find more effective strategies to combat hearing loss. These research and development programs are paying off. New solutions may reduce the number of future hearing loss cases, as well as provide novel treatments for personnel with an existing hearing loss.
The military is currently deploying a new hearing protection device, the Combat Arms Ear Plug. The Army, in cooperation with the French-German Institute of St. Louis, France, played a role in the device’s testing and development. This device transmits some environmental sounds, including the human voice, yet effectively attenuates damaging levels of acoustic trauma. It has doubtlessly reduced cases of hearing loss in current conflicts.
Research funded by the Office of Naval Research has shown that oxidative stress and free radical production leads to cochlear damage, as does excessive noise exposure. Many basic scientific studies have revealed that various antioxidant compounds may make the cochlea more resistant to noise damage when these compounds are given shortly before and during the noise exposure. These compounds reduce cochlear damage and permanent hearing loss for steady state noises, as well as acute acoustic trauma. Furthermore, these compounds when given even shortly after an unexpected noise exposure are capable of substantially reducing permanent hearing loss. The preliminary data of a study sponsored by the Navy, Army and Special Operations Command and involving more than 500 subjects suggests that the combined use of hearing protection devices and antioxidant supplements significantly reduces hearing loss when compared to only using earplugs.
Because of the high hearing loss rates associated with aviators and their crews and the higher noise levels associated with the new F-35 aircraft, in 2001, the military made investing in hearing protection a top priority. Also the DoD initiated a Defense Technology Objective called “Improved Aviation Personnel Hearing Protection.” DoD’s working groups are jointly planning, coordinating and executing relevant projects, with staffing from the Army, Navy, Air Force, NASA and industry in general. Major efforts include improving aircrew helmet specifications based on anthropomorphic data, improving effectiveness of noise-canceling headsets and developing pharmaceutical interventions.
In spring 2005, the U.S. Congress introduced the Military Quality of Life and Veterans Affairs Appropriations Act of 2006. The bill recommends funding for additional hearing conservation, as well as research and development resources. The Department of Veterans Affairs is concluding a congressionally mandated study on noise-induced hearing loss and tinnitus attributed to military service from World War II to the present. Also, the DoD’s Joint Chiefs of Staff Multi-Service Solution Task Force is seeking immediate solutions for hearing protection and communications for the current deployment in Iraq. Another success story is the development and fielding of hearing conversation by the DoD’s Defense Occupational and Environmental Health Readiness System. The military is using this application for testing and monitoring hearing for all military personnel at more than 800 testing sites worldwide. The Army is also working on improved aviator hearing protection and communications, as well as a similar system for soldiers. The U.S. Army Medical Research and Materiel Command is expanding the Military Operational Medicine Sensory Research Task Area to include pharmaceutical research into auditory problems. The scope will include protection, prevention, treatment and rehabilitation. Additional Army initiatives will reinforce hearing conservation in basic training, as well as providing hearing conservation measures at front lines of theater operations.
Many other examples of current military and military-sponsored commercial efforts could be given, further illustrating the military’s commitment to discovering and implementing solutions for this important problem. The military is not only considering how to better prevent acute acoustic trauma or treat noise-induced cochlear injury, but also leads the way in discovering novel solutions for those with long-term noise-induced hearing loss. Recent peer-reviewed research has shown the use of gene therapy may induce auditory sensory hair cell regeneration in mammals. The Office of Naval Research is sponsoring an ongoing study in the field of regeneration including the development of therapeutic molecule delivery that will be safe and effective in humans. Some day it may allow the recovery of hearing for people with chronic noise-induced hearing loss.
Deafness due to the din of battle is an old problem. As the battlefield, weapons and platforms become noisier, we experience new setbacks to preserving hearing, research the problems’ complexities and then develop novel solutions such as the ones currently being tested. The causes of noise-induced deafness are multi-factorial, and the solutions are likely to be as well. Future strategies will probably include diminishing the noise production of military vehicles; technical improvements in hearing protection devices and in complex noise-canceling headsets; medicines and supplements to make the ear more resistant to noise damage; and enhanced treatments for acute noise injury. One day, hair cell regeneration may even reverse chronic noise-induced hearing loss. Military hearing conservation programs should incorporate education, training and monitoring, and these three key elements should accompany technical advances. Meeting the hearing needs of military personnel is a key component to prevent hearing loss from becoming the military’s Achilles heel.
Richard “Rick” Kopke, M.D., retired (2004) U.S. Army Colonel, is director of Inner Ear Research at the Hough Ear Institute (HEI). A variety of clinical trials begun by Dr. Kopke are underway in the military to prevent and treat acute acoustic trauma and sudden hearing loss. Research teams are currently studying an oral treatment for acute acoustic trauma preventing and treating noise-induced hearing loss under grants from the Office of Naval Research.
