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Hearing Threshold Comparisons between 2001-02 NHANES and 2003-05 Fort Bliss U.S. Army Service Components

INTRODUCTION

Soldiers are exposed to unique noise hazards There are many dangerous effects of noise. Noise, if seen can be very harmful and has several disadvantages. These include:

1. Irritation. 2. Lack of sleep, leading to irritation. 3. Accidents and headaches are caused. 4. It may impair communication. 5. Causes dizziness. 6.
 from weapons fire, military training activities, and weapons systems, which place them at considerable risk for hearing loss. Noise-induced hearing loss noise-induced hearing loss Temporary or permanent hearing loss caused either by a single exposure to very loud sound(s) or by repeated exposure to louder sounds over an extended period. See Hearing loss.  has been considered unavoidable to soldiers despite the availability/use of hearing protection and other preventive measures because of extreme exposures exceeding the protective capability of hearing devices, skull transmission of intense noise, the element of surprise, and the combined effects of inhaled toxicants such as carbon monoxide carbon monoxide, chemical compound, CO, a colorless, odorless, tasteless, extremely poisonous gas that is less dense than air under ordinary conditions. It is very slightly soluble in water and burns in air with a characteristic blue flame, producing carbon dioxide;  with noise.1 A manifestation of noise exposure to this at-risk population is reflected by hearing loss being the most common and tinnitus Tinnitus Definition

Tinnitus is hearing ringing, buzzing, or other sounds without an external cause. Patients may experience tinnitus in one or both ears or in the head.
 the third most common service-connected disability among veterans.2 From 1977 to 2005, monetary payouts of hearing loss for all veterans amounted to over $7.4 billion, with the Army in 2005 alone having paid greater man $475 million for hearing loss disabilities, representing 52% of total cases for all branches of service mat year.3 A consequence of hearing loss is that it impacts mission readiness, mus making a soldier potentially nondeployable. Soldiers must have an acceptable hearing profile (H-1 or H-2)4 for deployability and combat readiness Synonymous with operational readiness, with respect to missions or functions performed in combat. , as determined by an audiometry test, which the Army offers regularly. Hearing profiles are one component in determining fitness for duty of soldiers. The algorithms for calculating mese profiles are published by the Army.5

The Army has stringent standards for defining noise hazardous environments,6 in which the limit for an 8-hour timeweighted average (TWA TWA Time-weighted average, see there ) for exposure to steady-state noise is 85 decibels (dB) using the A criterion to produce A-weighted sound pressure levels (dBA), whereas the Occupational Safety and Health Administration Occupational Safety and Health Administration (OSHA), U.S. agency established (1970) in the Dept. of Labor (see Labor, United States Department of) to develop and enforce regulations for the safety and health of workers in businesses that are engaged in interstate  (OSHA OSHA
n.
Occupational Safety and Health Administration, a branch of the US Department of Labor responsible for establishing and enforcing safety and health standards in the workplace.
) is less stringent defining permissible noise exposure for an 8-hour TWA at 90 dBA. To better protect soldiers' hearing, technological advancements have been made in personal protective equipment including sound attenuation Loss of signal power in a transmission.
Attenuation

The reduction in level of a transmitted quantity as a function of a parameter, usually distance. It is applied mainly to acoustic or electromagnetic waves and is expressed as the ratio of power densities.
 provided by me indoor/outdoor range E-A-R plug.7 In addition, studies have been conducted on the efficiency of hearing protectors Hearing protectors are devices designed to prevent Noise-Induced Hearing Loss (NIHL), a type of post-lingual hearing impairment.
  • Earplug - A device inserted into the ear canal.
  • Earmuffs - Objects designed to cover a person's ears.
 during weapons fire and use of vehicles and on the effects of hearing protection devices and their impact on sound localization Sound localization is a listener's ability to identify the location or origin of a detected sound or the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space (see binaural recording).  and orientation for soldiers.8,9

Studies show mixed results as to the effectiveness of the U.S. Army Hearing Conservation Program (HCP HCP,
n healthcare provider, a professional who specializes in treating and managing a person's general or specific health needs.
) in preventing hearing loss. A study comparing years in service of U.S. Army infantry, armor, and artillery enlisted personnel sampled in 1974 and 1989 shows mat the more recent 1989 populations had increased prevalence in acceptable hearing levels (H-1 profile in AR 40-501) across all time-in-service categories.10 In addition, the U.S. Army Center for Health Promotion and Preventive Medicine preventive medicine, branch of medicine dealing with the prevention of disease and the maintenance of good health practices. Until recently preventive medicine was largely the domain of the U.S.  (USACHPPM USACHPPM United States Army Center for Health Promotion and Preventive Medicine ) Website shows data on prevalence of H-3 or greater hearing profiles (i.e., nondeployable) for infantry, armor, and artillery in 1974 and 1994, respectively, as follows: Infantry (20.2% versus 7.8%), armor (19.3% versus 6.2%), and artillery (26.2% versus 7.1%).11 This comparison shows that there is not only a significant decrease in prevalence of nondeployable (i.e., >H-3) hearing profiles by 1994, but there is little difference in prevalence of mese Army hearing profiles between armor, artillery, and infantry.

Studies demonstrating continuing hearing loss include U.S. Army soldiers tested at military audiology audiology /au·di·ol·o·gy/ (aw?de-ol´ah-je) the study of impaired hearing that cannot be improved by medication or surgical therapy.

au·di·ol·o·gy
n.
 clinics after returning from deployments in 2003 and 2004 experiencing noiseinduced hearing loss injuries as compared to their nondeployed counterparts.1 A comparison of hearing threshold levels showed U.S. Army soldiers exposed to high noise levels were confirmed to have significantly worse hearing than those with limited noise exposure with these results also indicating a difference among race groups with African-American soldiers having lower hearing threshold levels than Caucasian soldiers.12

An additional method for evaluating the effectiveness of the U.S. Army HCP involves comparing hearing acuity of soldiers to mat of the civilian population. Surprisingly, there have been few published studies comparing these groups. To our knowledge, Ridgley and Wilkins (1991) conducted the only large-scale military and civilian population study.13 Ridgley and Wilkins (1991) compared 1984 audiograms from U.S. Army and Navy Active Duty populations with the 1971-74 audiograms from the National Health and Nutrition Examination Survey (NHANES NHANES National Health and Nutrition Examination Survey (US CDC)  I), which was considered representative of the entire U.S. population. This previous study determined that despite the armed forces screening policy to only allow individuals with acceptable hearing levels to initially join and remain within their respective departments, the Army and Navy Active Duty populations showed higher hearing threshold levels at 4 kHz compared to the NHANES I population, which did not have this exclusionary policy. Although the study was limited in scope by not separating military and NHANES I populations by gender,13 it did confirm the expectation that military populations in the 1980s had significantly worse hearing than the general population (i.e., NHANES I).

The purpose of this study is to use recent databases to determine whether there are significant (p < 0.05) hearing threshold differences between U.S. Army service components and the general population separated by gender.

METHODS

The military population (Army Active Duty, National Guard, and Reserve Component) evaluated in this study is represented by soldiers who underwent monitoring audiometry from January 2003 to March 2005 at the Fort Bliss Fort Bliss, U.S. army post, 1,122,500 acres (454,300 hectares), W Tex., E of El Paso; est. 1849 and named for Col. William Bliss, Gen. Zachary Taylor's adjutant in the Mexican War. Originally strategically located near the only ice-free pass through the Rocky Mts.  Hearing Conservation Service clinic. During this period of data collection, the U.S. Army was relying heavily on activated National Guard and Reserve units to fill a variety of roles in either Operation Enduring Freedom or Operation Iraqi Freedom. The Fort Bliss Hearing Conservation Service tested 9,096 Active Duty (AD), 3,842 National Guard (NG), and 2,025 Reserve Component (RC) soldiers comprising 394 military occupational specialties (MOS (1) (Metal Oxide Semiconductor) See MOSFET.

(2) (Mean Opinion Score) The quality of a digitized voice line. It is a subjective measurement that is derived entirely by people listening to the calls and scoring the results from
) with the following breakdowns: AD = 345 MOS types, NG = 21 1 MOS types, and RC = 228 MOS types. No single MOS represented >20% of any individual Army service component. Based on 2004-05 published values,14,15 the Fort Bliss sample population used in this study is estimated to represent -1.9%, 1.2%, and 1.1%, respectively, of the total U.S. Army Active Duty, National Guard, and Reserve Components. This is the same population used in the authors' previous study, which identified statistically significant (p < 0.05) differences in hearing profiles (i.e., H-1, H-2, etc.) by Army service component and gender.16 Because of diese previous findings, the hearing threshold data for this study were also grouped into Army service component and by gender.

Each Fort Bliss subject was tested in an Industrial Acoustics Company eight station acoustical enclosure that meets all ANSI (American National Standards Institute, New York, www.ansi.org) A membership organization founded in 1918 that coordinates the development of U.S. voluntary national standards in both the private and public sectors. It is the U.S. member body to ISO and IEC.  (1999) standards for ambient noise levels.17 The audiometers used were Benson CCA (1) (Common Cryptographic Architecture) Cryptography software from IBM for MVS and DOS applications.

(2) (Compatible Communications A
 200, formerly Maico 1000, automated microprocessing audiometers. These audiometers were properly calibrated cal·i·brate  
tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates
1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument):
 and met all ANSI (1996) standards.18 Subject test data were recorded and stored with the Defense Occupational and Environmental Health Readiness SystemHearing Conservation (DOEHRS-HC) software. Testing was conducted by technicians trained in accordance with the Council for Accreditation in Occupational Hearing Conservation (CAOHC CAOHC Council for Accreditation in Occupational Hearing Conservation
CAOHC China Aviation Oil Holding Company
) standards and DOEHRS-HC. Automated microprocessing audiometry follows me standard 10 down-5 up method for threshold determination. Methods for determining threshold and data entry are standardized across all Department of Defense components ensuring reliability and validity.

We used me 2001-2002 Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES)19 to represent the general U.S. population, which we also separated by gender. The NHANES audiometric au·di·om·e·ter  
n.
An instrument for measuring hearing activity for pure tones of normally audible frequencies. Also called sonometer.



au
 screening was performed using EARSCAN equipment20 on a sample of 1,872 U.S. adults (-0.0007% of U.S. population)21 ranging in age from 20 to 69 years also using the standard 10 down-5 up method automated microprocessing audiometry technique. Subjects using hearing aids Hearing Aids Definition

A hearing aid is a device that can amplify sound waves in order to help a deaf or hard-of-hearing person hear sounds more clearly.
 who were not able to remove mem for testing and subjects who had sufficient ear pain at the time of the exam that they could not tolerate headphones Head-mounted speakers. Headphones have a strap that rests on top of the head, positioning a pair of speakers over both ears. For listening to music or monitoring live performances and audio tracks, both left and right channels are required.  were excluded. There were no other precluding conditions for any part of the audiologic exam.

The data were analyzed using SAS (1) (SAS Institute Inc., Cary, NC, www.sas.com) A software company that specializes in data warehousing and decision support software based on the SAS System. Founded in 1976, SAS is one of the world's largest privately held software companies. See SAS System. . We calculated mean hearing threshold in decibels (dB) for me AD, NG, RC, and NHANES groups and for gender for a total of eight groupgender combinations. Individual mean hearing threshold was an average of the values for the right and left ear, a precedent established in previous studies.22-24 Because hearing loss for most broad-based noise occurs in tire 3-6 kilohertz One thousand cycles per second. See Hertz.  (kHz) frequency range but especially at 4 kHz,25 we compared mean hearing thresholds at 4 kHz between Army and civilian personnel. Following the example of previous studies,26,27 mean hearing thresholds were produced for group-gender combinations atme following age strata: <25, 25-29, 30-34, 35-39, 40-44, 45-49, and >50 years old. We calculated the 95% confidence interval confidence interval,
n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%.
 (CI) for each mean value, thus allowing a comparison of mean hearing thresholds of group/gender combinations by these age strata.

RESULTS

Table I shows mean age in years and the standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.

(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers.
 (SD) for each group-gender combination. The lowest mean ages occurred with AD females (26.5 years) and AD males (29.0 years); the highest mean ages occurred with NHANES females (41.7 years) and NHANES males (43.1 years), and mean ages of NG and RC were intermediate of these values. Because of the well-established medical effect of presbycusis (hearing loss as a function of age), the stratification of hearing thresholds by age allows for valid hearing threshold comparisons between study population.

Table II lists mean hearing threshold in decibels at 4 kHz frequency, standard deviation, count and calculated 95% confidence interval for the eight group-gender combinations by age strata. In general, mean hearing thresholds were significantly (p < 0.05) lower for all female groups at all age strata compared to the male groups, which supports results from previous studies of females in both the military and general population.23-26 Comparisons between males show that AD males generally had the lowest mean hearing threshold, NHANES and NG males had the highest mean hearing thresholds, and RC males were intermediate in value. Significant differences in mean hearing threshold between male groups only occurred between AD males and NG males at age strata of <25, 25-29, 30-34, and 35-59 years old, as well as between AD males and NG/NHANES males at >50 years old. Because the NHANES male population has older individuals in the >50-year-old age group, the comparisons at this age stratum must be viewed with caution.

DISCUSSION

This is the first large-scale study in ~20 years comparing hearing thresholds between the U.S. Army AD and general U.S. populations while also being the first study to present results for activated duty (i.e., NG, RC) populations. A limitation of this and all retrospective hearing studies is that exposure data are not available to correlate with hearing deterioration. Furthermore, data collected at the Fort Bliss Hearing Conservation clinic represented a convenient sampling population representing between 1 and 2% of the total AD, NG, and RC populations. Although this database has large sample sizes and includes 394 U.S. Army MOS types, it does not include all U.S. Army occupational specialties, and results may not be representative of the entire U.S. Army population.

A previous large-scale comparative study by Ridgley and Wilkins (1991) showed that 1984 Army AD hearing threshold levels were significantly higher than those of 1971-74 NHANES.13 The results of this previous study were expected because of the established noise exposure to the Army population placing them at risk for hearing loss. Ridgley and Wilkins ( 1 99 1 ), however, did not separate data by gender, but the historical predominance of male subjects in the U.S. Army implies that Army AD males had significantly higher hearing thresholds than NHANES males. Although AD males represented by the 2003-05 Fort Bliss database were still at risk for noise exposure, mean hearing threshold levels were not significantly different than the 2001-02 NHANES males, which contrasts with the previous findings of Ridgley and Wilkins (1991).

The AD male population had significantly lower mean hearing thresholds than the NG male population for numerous age strata. The reason for this difference is unknown as a result of our study being limited to a retrospective analysis. However, its impact on readiness and deployability is important. AD service members are required to have a DD 2215 (reference audiogram au·di·o·gram
n.
A graphic record of hearing ability for various sound frequencies.


Audiogram
A chart or graph of the results of a hearing test conducted with audiographic equipment.
) annually, whether they are deployed or not. This is not required for NG and Reserve soldiers. Workplace exposure to noise is more controlled in the AD population, whereas it is impossible to ensure that civilian workplaces provide the same control. In our experience at Fort Bliss, higher levels of hearing impairment hearing impairment
n.
A reduction or defect in the ability to perceive sound.
 in our NG and Reserve soldiers resulted in more frequent and more complicated evaluations which, in some cases, necessarily delayed deployment and prevented soldiers from serving in the combat theater. In the current situation, with U.S. military forces so heavily taxed, each delay or replacement means a real loss of combat power.

Our results are consistent with previous studies in showing that females have significantly lower hearing thresholds than males,28,29 but this study is the first to show no significant difference in hearing threshold between military and nonmilitary female populations. While considerable data from recent studies show that noise induced hearing loss still appears to be prevalent within an Army setting,1,12 this study shows no significant differences in mean hearing thresholds between the Fort Bliss AD population compared to that of NHANES. A number of observations could explain this: the selection and retention of soldiers for their physical health and exclusion of those with poor hearing, soldiers undergoing regular physical screening that is likely to pick up medical conditions See carpal tunnel syndrome, computer vision syndrome, dry eyes and deep vein thrombosis.  that could result in hearing loss, soldiers' lives are more regulated resulting in greater adherence to hearing protection protocols than their civilian counterparts, education, and training. Future investigations may be warranted to determine if the results of this study are representative for the entire U.S. Army and general populations.

CONCLUSIONS

This study provides baseline epidemiological information for 14,963 U.S. Army AD, NG, and RC soldiers enrolled from 2003-05 in the Fort Bliss Hearing Conservation Program and for 1,872 members of the general population represented by the 2001-02 NHANES database. Although data are limited and comparisons are imprecise, hearing thresholds for AD males have improved relative to NHANES males since a study was conducted comparing 1984 AD Army with 1971-74 NHANES populations. This study is consistent with previous studies showing that females have significantly better hearing than males.

ACKNOWLEDGMENTS

This study was approved by the Institutional Review Board (Research Protocol 05/19) at William Beaumont Army Medical Center William Beaumont Army Medical Center is a Department of Defense medical facility located in El Paso, Texas. It provides comprehensive care to all beneficiaries including active duty military, their family members, and retirees. .

© 2009 Association of Military Surgeons of the United States Provided by ProQuest LLC (Logical Link Control) See "LANs" under data link protocol.

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Author:Josef A PhD Sobieraj and Shawn G PhD Gibbs and Heath Steele and Mark D Harris and Patrick M PhD Tarw
Publication:Military Medicine
Date:Jan 1, 2009
Words:2347
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