|Year : 2016 | Volume
| Issue : 4 | Page : 275-279
Effect of noise pollution on hearing in auto-rickshaw drivers: A brainstem auditory-evoked potentials study
Bhupendra Marotrao Gathe1, Mahendra Bhauraoji Gandhe2, Babita Sahu3, Nitin Gosewade1, Chhaya Anil Saraf1, Ramji Singh4
1 Department of Physiology, Chandulal Chandrakar Memorial Medical College, Kachandur, Durg, India
2 Department of Biochemistry, Chandulal Chandrakar Memorial Medical College, Kachandur, Durg, India
3 Department of Dentistry, Shri Shankaracharya Institute of Medical Sciences, Bhilai, Chhattisgarh, India
4 Department of Physiology, All India Institute of Medical Sciences, Patna, Bihar, India
|Date of Web Publication||13-Oct-2016|
Bhupendra Marotrao Gathe
Department of Physiology, Chandulal Chandrakar Memorial Medical College, Kachandur, Durg - 490 024, Chhattisgarh
Source of Support: None, Conflict of Interest: None
Context: Auditory brainstem response is the most important tool in differential diagnosis and degree of hearing impairment. Many studies have been carried out to ascertain the effects of noise on human beings but very less on the transportation workers; hence, considering the need of time and use of brainstem auditory-evoked potentials (BAEP), this study was conducted to analyze the effect of noise pollution on auto-rickshaw drivers (ARDs). Aim: The aim of this study was to evaluate I, II, III, IV, and V wave latencies in ARDs and comparing it with control subjects in Central India. Settings and Design: This was a case-control study done on ARDs as participants and compared it with normal healthy individual BAEP pattern. Materials and Methods: We recorded BAEP from fifty healthy control subjects and fifty ARDs from the community of same sex and geographical setup. The absolute latencies were measured and compared. Recording was done using RMS EMG EP MARK II machine manufactured by RMS recorders and Medicare system, Chandigarh. Statistical Analysis Used: All the data related with subjects were filled in Excel sheet and analyzed with the help of EPI 6.0 info software with Student's t-test. Results: There were prolongations of all absolute wave latencies of II, III, IV, and V in the ARDs as compared to control subjects. Conclusions: The prolongation of all absolute latencies of II, III, IV, and V suggests abnormality in brainstem auditory pathway mainly affecting the retrocochlear pathways in group of ARDs (noise exposure >10 years) than other group who had exposed for <10 years and is more significant on the right ear than left.
Keywords: Auto-rickshaw driver, Brainstem auditory-evoked potential, Brainstem-evoked response audiometry, Central India, Noise pollution
|How to cite this article:|
Gathe BM, Gandhe MB, Sahu B, Gosewade N, Saraf CA, Singh R. Effect of noise pollution on hearing in auto-rickshaw drivers: A brainstem auditory-evoked potentials study. Indian J Otol 2016;22:275-9
|How to cite this URL:|
Gathe BM, Gandhe MB, Sahu B, Gosewade N, Saraf CA, Singh R. Effect of noise pollution on hearing in auto-rickshaw drivers: A brainstem auditory-evoked potentials study. Indian J Otol [serial online] 2016 [cited 2021 Aug 1];22:275-9. Available from: https://www.indianjotol.org/text.asp?2016/22/4/275/192179
| Introduction|| |
Noise is described as an unwanted sound but this is the subjective definition as one man's sound may be another man's noise. Physically, there is no distinction between sound and noise. The sound is a sensory perception and the complex pattern of sound waves labeled as noise, music, speech, etc., Environmental noise is a common cause of hearing loss in industrialized societies.  The World Health Organization estimated 360 million people (overall 5.3% of world population) with hearing disability in the world in 2012. 
Noise pollution chips away at the public health, interfering with our immune systems, learning, sleep, boosting stress hormones, and contributing to cardiovascular maladies, even at levels too low to cause hearing damage.  Community noise, also called as environmental noise, residential noise, or domestic noise, is defined as noise emitted from all sources except noise at the industrial workplace. The main sources of community noise include road, rail, and air traffic. When the noise exposure causing hearing loss is present in the workplace, it is referred to as occupational noise-induced hearing loss (NIHL). The NIHL is caused when the individual is exposed to noise intensity above 85 dB of sound pressure level, 8 h per day, regularly, for many years, usually setting in the first 5 years of exposure. 
Beginning with discovery of the cortical auditory-evoked potential (AEP) in 1939, until quite recently, the term objective test, when referring to the auditory system, denoted exclusively the measurement of neuroelectric events associated with auditory stimulation.  The discovery of AEP by Jewett and Williston marked the beginning of a variable revolution in the clinical application of auditory electrodiagnostic tests.  Every sensory-neural structure, when submitted to a stimulus, emits bioelectrical potentials as a response. Thus, the acoustic stimulation of the human auditory receptor triggers a number of electrical responses, or evoked potentials, which result in the successive activation of the cochlea and the neurons which make up the auditory pathway sequence of five major waves; these evoked potentials are the averaged electrical responses of the central nervous system following the repetitive auditory stimulation.  The short-latency AEPs comprise peaks of up to 10 ms after the stimulus and are presumably generated from the brainstem structures. Brainstem AEPs (BAEPs) are called for this part of AEPs. BAEPs have been applied widely to the examination of the integrity of brainstem nuclei and peripheral auditory pathways.  It comprises seven waves, of which waves I, III, and V are the most visible and of more significant clinical value. The currently used classification for the generating site of these waves is: (I) Distal portion of the auditory nerve relative to the brainstem; (II) proximal portion of the auditory nerve relative to the brainstem; (III) superior olivary complex; (IV) lateral lemniscus; (V) inferior colliculus; (VI) medial geniculate body; and (VII) auditory radiations.  Recordings of this potential may be clinically analyzed according to a number of parameters: Morphology; absolute latency and wave I, III, and V amplitudes; I-III, I-V, and III-V interpeak interval latencies; I-V latency and amplitude relation; and I-V interval interaural difference or wave V absolute latency difference (Centre for Science and Environment 2001).
Auditory brainstem response is the most important tool in differential diagnosis and degree of hearing impairment (whether cochlear or conductive), functional assessment of brainstem in patients with ischemic conditions or intracranial mass lesions. For interpretation of abnormal waves of BAEP, there is necessity of baseline BAEP pattern from healthy subjects. Many studies have been done to ascertain the effects of noise with the help of the audiometry on human beings but very less on the transportation workers; hence, considering the need of time and use of BAEP, this study was conducted to analyze absolute latencies of wave I, II, III, IV, and V in control subjects and auto-rickshaw drivers (ARDs) in Central India to analyze the effect of constant noise pollution on hearing.
| Materials and Methods|| |
This study was conducted in MGIMS, Sevagram, Wardha, Maharashtra, located in Central India during January 1, 2011-March 31, 2011. It was a case-control study on fifty apparently healthy normal subjects and fifty ARDs from the community of the same sex, age group, and geographical setup after consideration of the exclusion and inclusion criteria. ARDs were divided into Group 1 (noise exposure >10 years) and Group 2 (noise exposure < 10 years). The recording was done using RMS EMG EP MARK II machine manufactured by RMS recorders and medicare system, Chandigarh.
Fifty ARDs of public transport, having a minimum of 8-10 years of driving experience near city, and fifty apparently healthy normal male subjects of the age group (21-50 years) from the area of the Wardha city were selected.
The exclusion criteria included any middle ear disease such as chronic suppurative otitis media, otitis media with effusion and otosclerosis, Meniere's disease; systemic diseases such as Type 1 and Type 2 diabetes mellitus and hypertension, chronic use of ototoxic drug intake such as amikacin, gentamicin, and previous history of head trauma.
Nonprobability purposive sampling technique was used to select fifty ARDs and fifty subjects from the same geographical location of the Sevagram area of the Wardha City.
Before starting the study, proper ethical approval was obtained from the Institutional Ethical Committee, MGIMS, Sevagram, Wardha, Maharashtra, India.
After obtaining proper informed written consent from the participants in this study, all the subjects were informed about the nature of the study and method of BAEP recording. Their age, sex, and other details were recorded.
The BAEP procedure itself is safe and noninvasive; recordings were performed in a quiet room at constant room temperature of 30°C. Electrode application followed the international 10/20 system of electrode placement with one channel setting.
Silver chloride cup electrodes were attached on each earlobe (A1, A2), at the vertex (Cz, as the reference electrode, 10-20 international electrode placement system) and on the forehead (G as a ground electrode). The site of application was cleaned with an abrasive cleanser (spirit). A conductive paste was then applied to the electrode and placed over the prepared area [Table 1] and [Figure 1].
|Figure 1: Electrode placement in brainstem auditory-evoked potential study|
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|Table 1: Mean absolute latencies of control subjects and auto-rickshaw drivers with respect to noise exposure|
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Alternate (condensation and rarefaction) clicks were presented monaurally through earphones at a repetition rate of 11.1/s. The intensity of the click stimulus was 90 dB (decibels). 2000 responses were averaged for each record, each ear was tested separately, and at least two trials were performed on each subject.
Peak latencies, i.e., absolute latencies were measured from the leading edge of the driving pulse to the positive peaks. Waves VI and VII were not well identified in each and every subject in our setup, so we have not included their measurement in our study.
All the data related with subjects were filled in Excel sheet and analyzed with the help of EPI 6.0 info software (Manufacturer: Centre for Disease Control and Prevention, Atlanta, USA) with Student's t-test. We compared the absolute latencies of waves I to V for control subjects and ARDs with each and with previous studies on auditory-evoked response.
| Results|| |
Totally, 100 subjects included in the study were all male, of which fifty were control subjects and fifty were ARDs. ARDs were again grouped into two groups (with duration of noise exposure): Group 1 with <10 years and Group 2 with >10 years of noise exposure. Results are shown in [Table 1] and [Figure 2].
|Figure 2: The mean absolute latencies of control subjects and auto-rickshaw drivers with respect to noise exposure (C = control subjects; A <10 = auto-rickshaw drivers <10 years noise exposure; A >10 years = auto-rickshaw drivers >10 years noise exposure; R = Right ear; L = left ear)|
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| Discussion|| |
Wave I latency is a measure of electrophysiological activity of the eighth nerve. In the present study, it was 1.69 ± 0.13 and 1.67 ± 0.14 in control subjects in the right and left ears, respectively. It is comparable and consistent with the previous studies on normal subjects done by Lima et al. (1.68 ± 0.12), Hall et al. (1.65 ± 0.14), Misra et al. (1.67 ± 0.17), and Chiappa et al. (1.7 ± 0.15) as shown in [Table 2] and [Figure 2]. ,,, The values in ARDs Group 1 were 1.71 ± 0.13 and 1.7 ± 0.14 and in ARDs Group 2 were 1.73 ± 0.12 and 1.72 ± 0.09 in the right and left ears, respectively, which can be compared with the control subjects and appear to be raised in both groups of ARDs. In a study of Thakur et al. conducted on 24 ground crew and 12 normal subjects at Mumbai Airport, there is no significant alteration in wave I latencies indicative of retrocochlear involvement only.  In our study also, there are no significant differences in wave I latencies in control subjects and ARDs; hence, there must be retrocochlear affection of hearing pathways due to noise exposure. However, one of the previous studies by Santos et al., in 2009, on fifty bus drivers, twenty normal hearing subjects, they found the significant prolongation of wave I latencies compared to normal hearing subjects which is indicative of cochlear involvement due to the effect of noise. 
|Table 2: Normative data of peak latencies and interpeak latencies of previous studies|
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Wave II latency is a measure of electrophysiological activity of cochlear nucleus, and in our study, it was recorded 2.71 ± 0.22 and 2.75 ± 0.14 in control subjects appears to be raised in Group 1 (2.76 ± 0.15, 2.71 ± 0.21) and Group 2 (2.81 ± 0.19, 2.78 ± 0.22) of ARDs in the right and left ears, respectively.
Wave III latency is a measure of electrophysiological activity at the superior olivary nucleus, was recorded 3.71 ± 0.13 and 3.73 ± 0.21 in control subjects. It is comparable with the previous studies on the normal subjects done by Lima et al. (3.75 ± 0.21), Misra et al. (3.65 ± 0.22), and Munhoz et al. (3.7 ± 0.15).  In our study, the values were higher than the study by Soares Ido et al. (3.57 ± 0.18) and lower as compared with the study by Hall (3.8 ± 0.18) and Chiappa et al. (3.9 ± 0.19).  In study by Thakur et al., there is a prolongation of wave III in the noise-exposed ground crew (4.11 ± 0.24 and 4.09 ± 0.19) as compared with the normal hearing subjects (3.91 ± 0.30 and 3.79 ± 0.23) in right and left ears, respectively, but significant only on the right ear. Santos et al. found a significant difference in latencies of control subjects (3.52 and 3.45) and in exposed group (4.05 and 4.02) in the right and left ears, respectively. These studies were consistent with our study where there is a prolongation of latencies but more significant in Group 2 of ARDs on the right ear (3.90 ± 0.19) (P < 0.01) as compared to the left ear (3.93 ± 0.19) (P < 0.05) and also with Group 1, which were 3.91 ± 0.16 and 3.90 ± 0.14 in the right and left ears, respectively (P < 0.05).
Wave IV latency is a measure of electrophysiological activity in the lateral lemniscus of hearing pathway, and in our study, the latencies were 4.83 ± 0.28 and 4.85 ± 0.32 in control subjects, 4.91 ± 0.24 and 5.02 ± 0.14 in Group 1, and 4.93 ± 0.23 and 4.98 ± 0.21 in Group 2 of ARDs in the right and left ears, respectively. However, this was significant (P < 0.05) only in the left side in Groups 1 and 2 as compared to control subjects.
Wave V latency is a measure of electrophysiological activity in the inferior colliculus and prominent wave in the BAEP. In our study, latencies were 5.58 ± 0.23 and 5.61 ± 0.17 in control subjects. It is comparable with previous studies on normal subjects done by Lima et al. (5.56 ± 0.26), Hall (5.64 ± 0.23), Munhoz MSl et al. (5.6 ± 0.19), and Soares Ido et al. (5.53 ± 0.21). In the present study, the values were lower as compared with the study by Chiappa et al. (5.7 ± 0.25) and Misra et al. (5.72 ± 0.3) as shown in [Table 2]. In study by Thakur et al., there is a prolongation of wave V in the noise-exposed ground crew (5.99 ± 0.38 and 5.9 ± 0.34) as compared with the normal hearing subjects (5.62 ± 0.33 and 5.69 ± 0.07) in the right and left sides, respectively; however, this was significant only on the left side. Santos et al. found a significant difference in latencies of control subjects (5.52 and 5.48) and in exposed group (6 and 6.01) in the right and left sides, respectively. Murata et al. studied wave V latency with BAEP and found to be significantly prolonged in chain saw operators due to the effect of vibration and noise.  These studies were consistent with our study where there is a prolongation of latencies, but more significant in Group 2 of ARDs (5.93 ± 0.19 and 5.87 ± 0.186) (P < 0.01) as compared to Group 1 (5.82 ± 0.15 and 5.82 ± 0.14) (P < 0.05) in the right and left sides, respectively.
| Summary|| |
The control subjects and ARDs were divided according to the duration of exposure to noise for <10 years (Group 1) and >10 years (Group 2). BAEP recording was done for all subjects after ENT examination. Results were analyzed with the help of EPI info software and compared with the other studies in literature. After analysis of the results, it can be summarized as follows:
- There is a prolongation of all absolute wave latencies of II, III, IV, and V in the ARDs as compared to control subjects
- Prolongations of absolute latencies are more significant on the right side than the left side in the Group 2 than Group 1 of ARDs.
| Conclusion|| |
The prolongation of all absolute latencies of II, III, IV, and V suggests the involvement of brainstem auditory pathway mainly affecting the retrocochlear pathways in the noise-exposed group of ARDs of >10 years exposure than ARDs of <10 years exposure and is more significant on the right side than the left.
The authors are thankful to the auto-rickshaw drivers who participated in this study and also the BAEP technicians.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]