A study of effect of noise exposure on the hearing level of traffic personnel

 

Megha Kapoor¹, Manish Sharma^2*

 

{¹Demonstrator, Department of Physiology} {²Sr. Resident, Department of ENT and Head and Neck Surgery}

Government Medical College, Jammu, INDIA.

Email: meghabadyal247@gmail.com, maddys654@gmail.com

 

Abstract               Background: Noise is an important “stress factor” in the environment of people, nowadays. After age induced hearing loss (presbycusis), second most common type of sensorineural hearing loss is noise induced hearing loss (NIHL). Traffic personnel are one of the most vulnerable groups for NIHL. Material and Methods: 150 volunteered traffic personnel were studied for the effect of continuous exposure of noise on their hearing over a period of one year. Results: Noise induced hearing loss was observed in 22% subjects. Bilateral involvement was seen in 32%. Majority (69.69%) of the subjects had mild hearing loss. Noise induced hearing loss was more prevalent in subjects exposed to noise pollution for more than 3 years. Conclusion: Direct association was noticed between noise induced hearing loss and duration of exposure to noise. So, periodic checking of traffic policeman (clinically and audiologically) at frequent intervals of time is essential. Moreover hearing protective devices such as ear plugs and ear muffs should be provided to them during the duty hours.

Key Words: Presbycusis, Sensorineural hearing loss.

 

 

 

 

INTRODUCTION

Compression and rarefaction of particles in an elastic medium such as air and water is responsible for the production of sounds. Frequency of sound is measured in cycles/second or Hertz (Hz). Sound of frequencies less than 20Hz are called infrasonics and greater than 20,000 Hz are ultrasonics. Normally, human ear can hear sounds of frequencies between 20 to 20,000 Hz. The amplitude of a sound is expressed in decibel (dB). A range of 120 to 160 dB is classified as painful; 90 to 110 dB is classified as extremely high; 60 to 80 dB is classified as very loud; 40 to 50 dB is moderate; and 30 dB is faint.¹ Practically, there is no difference between sound and noise although sound is a sensory perception and noise corresponds to the undesired sound. By extension, noise is any unwanted disturbance within a useful frequency band.⁽²⁾. Noise has multiple adverse effects like elevated blood pressure, hearing loss, sleep disturbances etc. making noise pollution a public health concern although it has not been well addressed.³ Noise-induced hearing loss (NIHL) is second only to age induced hearing loss or presbycusis. It occurs as a result of exposure to recreational and occupational noise that results in damage to hair cells of the cochlea in the inner ear. These hair cells are very important components of the inner ear that are responsible for conversion of sound energy to electrical signals transmitted to the brain. Most of the times, prolonged noise exposure causes NIHL but sudden exposure to an intense sound such as an explosion, sometimes referred to as an acoustic trauma, heard at one instance can lead to NIHL. In general, the amount of noise required to cause permanent damage from chronic exposure is anything equivalent to 10 years or more at a level of 85 dB for more than 8 hours a day.^4,5 The maximum hearing loss due to noise exposure is 40 dB at low frequency and 75 dB at high frequencies but when the effects of presbycusis are added, the thresholds may become greater.^6,7 Noise-induced hearing loss generally occurs slowly over time, and the full effects are usually not realized until after 10-15 years of chronic noise exposure.^(8,9) However, some NIHL may be evident after a single exposure to loud noise.¹⁰ There are very few studies carried out regarding the estimation of noise levels and auditory effects of noise generated by automobiles among traffic policeman in India. Moreover, the slow nature of noise induced hearing loss keep the majority of the patients unaware of the effects of noise pollution.

MATERIALS AND METHODS

The present cross-sectional study was undertaken in the Department of Physiology, Santosh Medical College, Ghaziabad from 2014 to 2015 to assess the magnitude and ill effects of noise exposure on the hearing level of traffic personnel. Traffic policemen working in different parts of Ghaziabad city were included as subjects. After explaining the purpose and methodology of the study, all the subjects found eligible were requested to participate in the study. A pre-enrolment examination was conducted on them to ensure that they had a normal hearing. A written consent was obtained from all the subjects. They underwent systemic and ENT examination to detect any obvious pathology which might result in hearing loss. Their age, sex, duration of the job in years and working hours were recorded by the investigator. All the subjects suffering from pre-existing diseases ear disease such as chronic suppurative otitis media, otitis media with effusion, otosclerosis, throat infection, those on ototoxic drugs, suffering from any systemic disease such as hypertension or diabetes mellitus were excluded. The below labelled tests were carried out on the recruited subjects to assess the degree of hearing loss among the participants:

1. Otoscopy
2. Tuning fork tests
3. Rinne’s test
4. Weber’s test
5. Absolute bone conduction test
6. Schwabach’s test
7. Pure tone audiometry (PTA)

Sound Pressure Level (SPL) was measured with the help of instrument called Sound Level Meter (SLM)-100 manufactured by Envirotech Instruments Pvt Ltd, New Delhi with Acoustic Calibrator, Model-2000, Type-2 with accuracy of + 0.5 dB at 25 degree Celsius. The SPL was mounted on a tripod stand to avoid any effect due to body shaking and the measurements were taken at different crossings and places during the peak hours of the traffic, where traffic policemen were discharging their duties for about 8 to 12 hours per day.

 

OBSERVATIONS

150 healthy traffic policemen deputed in different parts of Ghaziabad city and who had been working for a period of minimum one to maximum five years, volunteered for our study. Most of the subjects were in the age group of 30 to 39 years (56.67%), while minimum number of subjects were in the age group of >50 years (8%), with mean age of the study being 36.65 ( +6.61 ) years. Maximum numbers of subjects (39.33%) were exposed to noise pollution for a period ranging 2 to 3 years. 21 (14%) subjects were exposed to >4 years of noise pollution. 5 subjects had pollution exposure of 5 years. Noise induced hearing loss, which was defined as selective 4000Hz hearing loss >30 dB was observed in 33 cases (22%) and sensorineural hearing loss was observed in 8 (5.33%) subjects, whereas 109 traffic personnel were having normal hearing [Table 1].

 

Table 1: Distribution of study group according to degree of hearing loss by audiometric tests (n=150)

Amongst all the 33 NIHL cases, mild impairment (26-40 dB) was seen in most of the patients followed by moderate impairment (41-55dB). In our study, subjects with <40 years age have more number of noise induced hearing loss cases as compared to the subjects in > 40 years of age. Noise induced hearing loss is seen more in subjects who were exposed to the traffic noise for a period of more than 3 years as compared to those exposed for a period up to 3 years [Table 2].

 

Table 2: Comparison of NIHL with duration of exposure

Table 3 shows mean hearing threshold at 4 kHz according to age showing most of the subjects with mild to moderate hearing loss (more in right as compared to left).

Table 3: Mean hearing threshold at 4 kHz according to age (in dB)

Table 4 shows mean hearing threshold at 4 kHz according to the duration of exposure.

Table 4: Mean hearing threshold at 4 kHz according to duration of exposure (in dB)

 

DISCUSSION

Noise is defined as unpleasant sound that the listener does not want to hear.¹¹ Noise induced hearing loss (NIHL) is one of the causes of Sensorineural hearing loss (SNHL) which occurs as a result of damage to the outer hair cells of the cochlea in the inner ear. It is a permanent hearing impairment resulting from prolonged exposure to high levels of noise.¹² It is the most common cause of sensorineural hearing loss which is preventable. High frequencies are affected first, typically at 4 kHz, followed by middle and lower frequencies.¹³ The problem needs to be addressed as there is no medical therapy for hearing loss caused by noise. Once established, the hearing loss is irreversible.⁽¹⁴⁾ Internationally, the contribution of occupational noise exposure to total deafness rates is approximately 7% in the most developed nations and 21% in developing countries.¹⁵ This study was conducted on 150 healthy traffic policeman to detect noise induced hearing loss in them with duration of 1 to 5 years. Out of 150 subjects, Noise induced hearing loss was observed in 33 subjects and sensorineural hearing loss was observed in 8 subjects, whereas normal hearing was found in 109 subjects. The results are in accordance with some studies done earlier who assessed the traffic noise and its impact on traffic policeman and observed a high incidence of noise induced hearing loss (21%) and of sensorineural hearing loss (18%) in these persons¹⁶, whereas incidence of noise induced hearing loss of 22.9% was found among the air force personnel.¹⁷ Our study is not in agreement with a study conducted in Malaysia, who studied noise exposure and noise induced hearing loss among Kuala Lumpur traffic point duty personnel and found that 80% were positive for noise induced hearing loss.¹⁸ Amongst all the 33 NIHL cases, most of the subjects had mild impairment (26-40 dB) followed by moderate impairment (41-55dB) which is consistent with a study who concluded that 24% of the traffic policeman of Dhaka had mild to moderate sensorineural hearing loss due to noise exposure which was related to duration of exposure.¹⁹ Our study showed right sided predominance, which is in consonance with a study who also reported right sided hearing loss.¹⁷

 

 

CONCLUSION

Direct association was observed between noise induced hearing loss and duration of exposure to noise. Keeping in mind the above facts, the duration of exposure of traffic persons to noise pollution must be less than three continuous years for exposure limitation. Regular checking of traffic policeman (clinically and audiologically) should be done at frequent intervals of time. Traffic policemen should be provided with hearing protective devices such as ear muffs, ear plugs and ear canal caps free of cost. Awareness should be created among traffic policemen about the auditory and non-auditory effects of noise by implementing education and training programs.

 

REFERENCES

• Barrett KE, barman SM, Boitano S and Brooks HL. Hearing and equilibrium. In: Ganong’s Review of Medical Physiology, 23^rd edition. Tata McGraw Hill Edition, New Delhi 2010; chapter 13:209.
• National Institute of Occupational Safety and Health (NIOSH). Criteria for a recommended standard: occupational noise exposure- revised criteria, 1998. Cincinnati (OH): US Department of Health and Human Services 1998; publication number 98-126.
• Goines L and Hagler L. Noise pollution: a modern plague. Southern Med J 2007; 100:287-294.
• Rabinowitz, P. Noise-induced hearing loss. Am Fam Phys 2000; 61:2749-56, 2759-60.
• National Institute of Deafness and Other Communication Disorders (NIDCD). Fact Sheet: Noise-induced hearing loss. NIH Publication 2007; 97(4):4233.
• Kircher DB. Noise-induced hearing loss. J Occup Environ Med 2003; 45(6):579-581.
• Kircher DB, Evenson E, Dobie RA, Rabinowitz PM, Crawford J, Kopke R and Hudson TW. Occupational noise-induced hearing loss. ACOEM Task Force on Occupational Hearing Loss. J Occup Environ Med 2012; 54(1):106-108.
• Miller JD. Effects of noise on people. J Acoust Soc Am 1974; 56:729-764.
• Albera R, Lacilla M, Piumetto E and Canale A. Noise-induced hearing loss evolution: influence of age and exposure to noise. Eur Arch Oto-Rhino-Laryngol 2009; 267:665-671.
• Melnick W. Human temporary threshold shift and damage risk. J Acoust Soc Am 1991; 90(1):147-153.
• Plog BA and Quinlan PJ. Fundamental of Industrial Hygiene, 5^th edition, National Safety Council, New York, 2002.
• Fauci, Braunwald, Kasper, Hauser, Longo, Jameson and Loscalzo. Harrison’s Principles of Internal Medicine. USA: McGraw Hill 2008; 1:202.
• Isaacson JE, Vora N and Hershey MS. Am Fam Phys 2003; 68(6):1125-1132.
• American Health. (ISS No. 730-7004) 1992 (January-February); 7:58-62.
• Thorne PR, Ameratunga, Stewart J, Reid N, Williams W, Purdy SC, Dodd G and Wallaart J. Epidemiology of noise induced hearing loss in New Zealand. J NZ Med Assoc 2008; 121:1280.
• Rajenderkumar D. Assessment of traffic noise and its impact on certain personnel. Indian J Otolaryngol Head Neck Surg 1997; 49(1):47-50.
• Nair S and Kashyap RC. Prevalence of noise induced hearing loss in Indian Air Force personnel. Medical J Armed Forces India 2009; 65(3):247-251.
• Thomas N, Mariah AN, Fuad A, Kuljit S and Philip R. Noise exposure and noise induced hearing loss among Kuala Lumpur traffic point duty personnel. Med J Malaysia 2007; 62(2):152-155.
• Sharif A, Taous A, Siddiqui BH and Dutta PG. Prevalence of noise induced hearing loss among traffic police in Dhaka Metropolitan City. Mymensingh Med J 2009; 18(1):24-28.