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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 22  |  Issue : 3  |  Page : 199-202

Short-term audiometric profile in army recruits following rifle firing: An Indian perspective


Department of ENT, Command Hospital, Lucknow, Uttar Pradesh, India

Date of Web Publication8-Aug-2016

Correspondence Address:
Dr. Arpit Saxena
Room No. 204, SR Hostel, DTH, UPRIMS and R, Saifai, Etawah, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-7749.187984

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  Abstract 

Aim: This study is aimed to assess the short-term audiometric profile in army recruits with green ears following rifle firing. Materials and Methods: A total of 100 fresh army recruits were selected by simple randomization. Recruits with a history of firearm exposure and ear surgery were excluded. Screened recruits underwent pure tone audiometry (PTA) by modified Hughson-Westlake method 1 day before firing. Recruits fired 100 rounds from 5.56 mm Indian Small Arm System rifle in a single session as per standard military protocol. After firing, recruits reported within 4 h for repeat evaluation. Ear complaints such as tinnitus and hearing loss were recorded and repeat PTA was performed. Recruits having standard threshold shift (STS) were not exposed to further firing and called for an evaluation of hearing after 2 weeks. Student's paired t-test and Chi-square test were used to analyze the results. Results: The mean age of subjects was 19.69 ± 0.61 years old. After rifle firing by the 100 recruits, 16 subjects (16.0%) had complaints of hearing loss and tinnitus. Only tinnitus was seen in further 11 subjects. Twelve subjects were found to have STS. In four subjects audiogram showed audiometric notch two being at 2 kHz, one at 4 kHz and one at 6 kHz. Double notch was observed in none of the audiograms. All subjects were asymptomatic at the end of 2 weeks after firing. P< 0.05 was considered significant. Conclusion: Short-term audiometric profile of army recruits shows there is a significant change in audiometric thresholds immediately after firing which recover back to normal within 2 weeks.

Keywords: Army recruits, Audiometric profile, Green ears, Rifle firing, Standard threshold shift


How to cite this article:
Saxena A, Ramesh A V, Mehra PR, Singh D K. Short-term audiometric profile in army recruits following rifle firing: An Indian perspective. Indian J Otol 2016;22:199-202

How to cite this URL:
Saxena A, Ramesh A V, Mehra PR, Singh D K. Short-term audiometric profile in army recruits following rifle firing: An Indian perspective. Indian J Otol [serial online] 2016 [cited 2019 Oct 16];22:199-202. Available from: http://www.indianjotol.org/text.asp?2016/22/3/199/187984


  Introduction Top


Noise is acoustically made up of numerous sound waves with anarchically distributed amplitude and phase ratios, causing an unpleasant sensation.[1] Impact noises are usually produced by quick gas expansion, such as that produced by firearms or bomb explosions. When the human ear is exposed to impact noise, it can lead to abrupt lesions in the cochlea, basement membrane rupture and hair cell disarray. Clinically, consequence of impact noise is an immediate unilateral or bilateral hearing loss with or without tinnitus. In some cases, the hearing loss may improve after a few days.[2] Such a reversible elevation of auditory threshold produced by noise exposure is known as temporary threshold shift (TTS). Constant exposure to intense noise causes damage to the outer hair cells, especially those on the cochlear basal turn as this is the area which is commonly stimulated.[3] This produces an irreversible elevation of auditory threshold known as permanent threshold shift. One of the industries which expose its workers to high noise levels is the military, especially when practicing with firearms. The firearm explosion noises are the number one cause of noise-induced hearing loss (NIHL) in the United States.[4] Occupational Safety and Health Association (OSHA), (USA) defines standard threshold shift (STS) as a change for the worse in either ear of 10 dB or more in the average of thresholds at 2, 3, and 4 kHz relative to the baseline.[5]

In the Indian Army, a large number of fresh recruits who have never been exposed to gunfire are exposed to rifle firing for the first time. There exists inadequate data on the incidence of TTS in green ears of recruits in the Indian scenario. This study is aimed to assess the short-term audiometric profile in army recruits with green ears following rifle firing.


  Materials and Methods Top


Fresh army recruits were selected from the regional regimental center. They were evaluated at Department of ENT. Recruits with a history of firearm exposure and ear surgery were excluded. A thorough general and ENT examination was done. Tympanic membrane status and free field hearing were recorded. Subjects with abnormal tympanic membrane were excluded. Recruits underwent pure tone audiometry (PTA) by modified Hughson-Westlake method in an appropriately sound treated audiometry chamber. Air and bone conduction thresholds were recorded from the frequency of 500 to 8000 Hz for both the ears and wherever necessary masking was done. Pure tone average is taken as average of pure tone thresholds at 500, 1000, 2000 Hz frequency. Subjects with air conduction pure tone average of >20 dB were excluded.

Registered recruits fired 100 rounds of Indian Small Arm System 5.56 mm caliber rifle in a single session as per standard military protocol without any ear protection. After firing, recruits reported to ENT Department for a repeat evaluation on the same day. Changes in the ear following rifle firing were recorded in the form of complaints such as tinnitus and hearing loss. Tympanic membrane status was assessed. PTA air conduction threshold was recorded. Recruits having STS were called for an evaluation of hearing after 2 weeks. During 2 weeks these recruits were not exposed to further rifle firing. Third PTA was done to record changes in air conduction pure tone thresholds if any.

All the data were recorded and compiled. Student's paired t-test was used to assess the significance of the difference of mean values before and after firing (immediately and after 2 weeks). Chi-square test was used to assess level of significance. P < 0.05 was considered significant in this study.


  Results Top


All the subjects were male. The minimum age was 18 years, and the maximum was 21 years with a mean of 19.69. Four subjects (4.0%) were left-handed and fired from left shoulder and rest fired from the right shoulder.

After firing, 27 subjects complained of tinnitus, right ear 7, left ear 12, and bilateral 8. Hearing loss was a complaint in 16 subjects, right ear 4, left ear 10, and bilateral 2. No giddiness and tympanic membrane perforation was noticed.

Frequency specific air conduction thresholds with standard deviation before and after firing are presented in [Table 1] and [Table 2], respectively.
Table 1: Prefiring thresholds

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Table 2: Immediate postfiring thresholds

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Pure tone average of thresholds at 500, 1000, and 2000 Hz was calculated for both ears separately, before, and after firing. Pure tone average in the right ear was 6.54 dB before firing and 7.67 dB after firing. In the left ear, the pure tone average changed from 8.14 to 8.91 dB after firing.

In the distinct analysis of frequencies, the differences in hearing thresholds before and after exposure was significant in the frequency of 3000 Hz in right ear and (P < 0.05) and it was significant in the frequencies of 1500, 3000, 4000, and 6000 Hz in left ear.

As per OSHA guidelines 12 subjects were found to have significant threshold shift. Mean age of these subjects were 19.33 years. Out of 12 subjects four had STS in both ears, four each in the right and left side. All subjects who had STS were right handed. The range of STS (as compared to baseline) varied from 18 to 43 dB (air conduction thresholds). Audiogram of four subjects showed an audiometric notch, two at 2 kHz, one at 4 kHz and one at 6 kHz. Double notch was not observed in any of the audiograms.

Prefiring audiograms of subjects with STS were studied to look for possible indicators of susceptibility to STS. Prefiring audiograms of all subjects with STS were unremarkable.

Two weeks after firing, all subjects with STS had normal auditory thresholds. There were no complaints of tinnitus and hearing loss.


  Discussion Top


The present study is conducted on fresh army recruits who have never been exposed to firearm earlier (green ears). Glorig in 1958 published that green ears had greater TTS than those whose ears have been exposed for a long period (ripe ears).[6] There is relative lack of data on TTS in green ears in last 50 years.

The mean age of subjects in the present study was 19.69 ± 0.61 years and sex being all male. The age of the subjects was in the range of 18–21 years. Rezaee et al. studied impulse noise level and acoustic trauma in military person in Tehran and mean age of subjects being 20.08 ± 2.61 years and all being male.[7] Munjal and Singh demonstrated the importance of age in that with an increase in age and service of personnel, the hearing loss also increased. In the age group of 21–25 years, hearing loss was between 56 and 65 dB. Whereas in 41–45 years age group hearing loss was between 81 and 90 dB.[8]

In the present study, four subjects were left-handed (4%), and 96 were right-handed (96%). Immediately after firing, the symptom of hearing loss with tinnitus was present in 16 (16%) subjects; only tinnitus was present in 11 (11%) subjects, and only hearing loss was present in none subject. All were right handed. Hearing loss was left sided in ten (10%) subjects, right in four (4%) subjects and bilateral in two (2%) subjects. All these patients were asymptomatic 2 weeks after firing. In the study by Ghasemi et al. three subjects (7.5%) were left-handed and eight subjects out of 40 (20%) reported hearing loss within 3 h of firing. Assessment of complaints after 1 week showed hearing loss in three subjects (7.5%).[9] Rezaee et al. found that of forty subjects, four subjects had unilateral hearing loss and two had bilateral hearing loss immediately after firing of which one subject with bilateral hearing loss improved after 1 week.[7] Moon studied hearing loss in 3650 right handed army soldiers in Korea and found hearing loss with tinnitus in 7 (0.001%) subjects immediately after firing. After 3 months all affected subjects were normal.[10]

Tinnitus was a predominant symptom in 11 subjects immediately after firing, all of whom improved at the end of 2 weeks. In this study, none of subjects reported giddiness or tympanic membrane perforation. Tinnitus was also a predominant symptom in study by Ghasemi et al., 52.5% reducing to 7.5% after 1 week. They also reported an incidence of 32.50% giddiness and 2.5% ruptured drum immediately after firing.[9] Rezaee et al. report an even higher incidence of tinnitus 62.5%, all of whom were a symptomatic after 1 week. Dizziness was seen in 16 subjects (40%), and none was symptomatic after 1 week. In one subject (2.5%), rupture of the tympanic membrane was evident immediately after firing.[7]

In the present study, 2 weeks period was considered as a period of recovery of TTS. All subjects having TTS recovered during this phase. In Ghasemi et al. study, 1 week was considered as recovery period, and 2.5% still had threshold shift after 1 week.[9] Munjal and Singh studied impulse noise trauma from heavy weapon in Indian Army and found recovery period of 61% ears within 6 h, 78.5% within 24 h, and 9.5% subjects did not show recovery even after 3 weeks.[8] Rezaee et al. considered 1 week as recovery period and 37.5% subjects showed hearing loss after 1 week.[7] Moon found recovery of all TTS subjects in 3 months.[10] Some studies do not reveal any hearing loss like Celli et al. studied effect of impulse noise of gunshot by military men with ear defenders and found no significant TTS.[11]

In present study for distinct analysis of frequencies, the differences in hearing thresholds before and after exposure was significant in the frequency of 3000 Hz in right ear (P < 0.05) and was significant in the frequencies of 1500, 3000, 4000, and 6000 Hz in left ear. Although 96% subjects were right handed but most significant changes were seen in left ear as stated above. Rezaee et al. compared audiometry results in different frequencies before and 15 min after exposure and showed that there was a significant difference at 500 Hz (P < 0.001), 1000 Hz and 4000 Hz in the right ear. In the left ear, however, there was no significant difference at any frequency.[7] In study by Ghasemi et al. most significant shift in hearing thresholds was seen at 4 kHz.[9]

In this study, significant threshold shift (STS) was seen in 12 subjects. Mean age of these subjects were 19.33 years. Of 12 subjects four had STS in bilateral ears, four in the right side and rest four in the left side. All subjects who had STS were right handed. The range of STS (as compared to baseline) varied from 18 to 43 dB (air conduction thresholds). In Rezaee et al. study three participants (7.5%) of the total forty participants had STS in right ear within 3 h of firing.[7] All STS recovered within 1 week. A study done by Munjal and Singh revealed STS of 57% right ears and 63% in left ears. The air conduction thresholds after firing in the right ear were 46–65 dB and 51–75 dB in left ear.[8]

A total of four subjects had audiometric notch, two at 2 kHz, one each at 4 kHz and 6 kHz. McBride and Williams did not find significant correlation between different types of exposure to noise and a classic sign of NIHL, the audiometric notch. They concluded that to diagnose NIHL, it is important to elicit a detailed and accurate history of exposure to noise. Although the notch at 4 kHz is a well-established clinical sign and may be valuable in confirming the diagnosis, the 6 kHz notch is variable and of limited importance.[12] Nair and Kashyapstudied the classical audiometric notch at 4 kHz (Aviators notch) as mentioned in the literature as pathognomic of NIHL was seen replaced by 6 kHz notch in a significantly large number of Indian Air Force personnel. This study emphasizes the importance of early involvement of 6 kHz in the present noise environment in detecting NIHL.[13] Chung describes 27 cases of NIHL with double notch, one at low frequency and one at high frequency.[14] However, our study did not reveal any audiograms with double notches.

In this study, hearing evaluation was done before and after exposure to rifle firing. While, in many studies cross-sectional sampling, was used.[11],[15] The preexposure hearing thresholds were used as controls. No separate control group was included in the study. Study could have been expanded with the inclusion of otoacoustic emissions (OAE) in evaluation protocol as OAE are considered to be more sensitive by many. Another limitation of the present study is absence of a “ripe ear” arm to compare with “green ear” arm.

The results of this research make the necessity of attention to auditory health of military personnel during training period more obvious. Therefore, clinical evaluation after exposure to impulse noises at appropriate intervals by using PTA cannot be over emphasized.


  Conclusion Top


In this study, there are significant changes in audiometric thresholds immediately after firing as compared to baseline (prefiring). The effect of subjective complaints of hearing loss and tinnitus was more prominent in opposite ear immediately after firing. PTA thresholds showed change in audiometric thresholds in high frequencies, commonly at 6 kHz. Significant threshold shift was seen in 12% of subjects. Audiometric notch was seen in a small number of subjects but not necessarily classically at 4 kHz. Short-term audiometric profiles of army recruits show significant change in audiometric thresholds immediately after firing and recover back to normal within 2 weeks.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
de Almeida SI, Albernaz PL, Zaia PA, Xavier OG, Karazawa EH. Natural history of occupational hearing loss induced by noise. Rev Assoc Med Bras 2000;46:143-58.  Back to cited text no. 1
    
2.
Bento RF, Miniti A, Marone SA. Noise induced otolagia. São Paulo: Editora USP; 1998. p. 274-82.  Back to cited text no. 2
    
3.
Alberti PW. Hearing loss in individuals of pelo ruído. In: Lopes OF, Campos AH, editors. Tratado de Otorrinolaringolgia. São Paulo: Roca; 1994. p. 934-49.  Back to cited text no. 3
    
4.
Stewart M, Pankiw R, Lehman ME, Simpson TH. Hearing loss and hearing handicap in users of recreational firearms. J Am Acad Audiol 2002;13:160-8.  Back to cited text no. 4
    
5.
NCHA professional guide for audiometric baseline revision appendix IV: EH Berger. The Noise Manual. Revised 5th ed: American Industrial Hygiene Association; 2003. p. 756-58.  Back to cited text no. 5
    
6.
Glorig A. Noise and Your Ear. New York: Grune and Stratton; 1958.  Back to cited text no. 6
    
7.
Rezaee M, Mojtahed M, Ghasemi M, Saedi B. Assessment of impulse noise level and acoustic trauma in military personnel. Trauma Mon 2012;16:182-7.  Back to cited text no. 7
    
8.
Munjal KR, Singh VP. Impulse noise trauma during army weapon firing. Indian J Otolaryngol Head Neck Surg 1997;49:165-8.  Back to cited text no. 8
    
9.
Ghasemi M, Saedi B, Mojtahed M, Najafabadi MR, Afshari M, Izadi M. Hearing threshold shift measured by pure tone audiometry after gunshot exposure in military personnel not using hearing protectors. Iran J Mil Med 2012;13:201-6.  Back to cited text no. 9
    
10.
Moon IS. Noise-induced hearing loss caused by gunshot in South Korean military service. Mil Med 2007;172:421-5.  Back to cited text no. 10
    
11.
Celli A, Ribas A, Zannin PH. Effect of impulsive noise on military personnel- A case study. J Sci Ind Res 2008;67:605-8.  Back to cited text no. 11
    
12.
McBride DI, Williams S. Audiometric notch as a sign of noise induced hearing loss. Occup Environ Med 2001;58:46-51.  Back to cited text no. 12
    
13.
Nair S, Kashyap RC. Significance of 6 kHz in noise induced hearing loss in Indian air force personnel. Indian J Aerosp Med 2008;52:15-20.  Back to cited text no. 13
    
14.
Chung DY. Meanings of a double-notch audiogram. Scand Audiol 1980;9:29-32.  Back to cited text no. 14
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15.
Ayub Z, Ahmed A. Noise induced hearing loss amongst artillery soldiers. Pak Armed Forces Med J 2011;61:61-3.  Back to cited text no. 15
    



 
 
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