|Year : 2014 | Volume
| Issue : 4 | Page : 203-207
Brainstem evoked response audiometry in stone cutting workers at a construction site
Roohi Aboobackr, Balaji W Ghugare, Mukesh R Dinkar
Department of Physiology, GMERS Medical College Gotri Vadodara, Gujarat, India
|Date of Web Publication||13-Dec-2014|
Balaji W Ghugare
GMERS Medical College, Gotri, Vadodara 390 021, Gujarat
Source of Support: None, Conflict of Interest: None
Context: Noise-induced hearing loss (NIHL) is the most prevalent and preventable occupational disease in developing countries. Manufacturing industry workers and other sector industries with special profession where exposure to noise is inevitable are the victims of NIHL. Pure tone audiometry has widely been used to establish the prevalence of NIHL. Brainstem evoked response audiometry (BERA) offers an objective assessment of the auditory pathway from receptor to cortex. Aims: With paucity of data among stone cutting workers, the present study evaluated this cohort using BERA to assess involvement of the auditory pathway. Settings and Design: A cross-sectional study. Materials and Methods : A total of 31 cases and 30 controls underwent BERA after its selection following inclusion and exclusion criteria. Statistical Methods : Data obtained was compared using unpaired student's t-test between means of cases and controls. Results: Absolute peak BERA waveform I, III and III latencies on left side and wave I latencies on the right side showed significant prolongation (P < 0.05). Inter-peak latencies I-III, I-V, and III-V differences were non-significant. Mode BERA threshold values were 60 dB and 40 dB for cases and controls respectively. Conclusion: Study concluded with the observations that, workers engaged in stone cutting are at the risk of developing NIHL (mild to moderate) that may affect the peripheral component of the auditory pathway.
Keywords: And auditory pathway, Brainstem evoked response audiometry, Noise induced hearing Loss, Pure tone audiometry
|How to cite this article:|
Aboobackr R, Ghugare BW, Dinkar MR. Brainstem evoked response audiometry in stone cutting workers at a construction site. Indian J Otol 2014;20:203-7
| Introduction|| |
Excessive noise is a global occupational health hazard with considerable social and physiological impacts, including noise-induced hearing loss (NIHL). Worldwide, 16% of the disabling hearing loss in adults is attributed to occupational noise, ranging from 7% to 21% in the various subregions. The effects of the exposure to occupational noise are larger for males than females in all subregions and higher in the developing regions. Occupational noise is a significant cause of adult-onset hearing loss.  NIHL is the most common occupational disease except work-related diseases such as musculoskeletal disorders and cerebrovascular diseases, and NIHL prevalence is thought to be much higher than reported in official publications.  NIHL is a serious health problem in Asia. The highest attributable fraction of adult-onset hearing loss resulting from noise exposure in the world comes from Asian countries. It is the most prevalent and preventable occupational disease in most Asian countries. Sources of noise in these countries include manufacturing and agriculture industries, exploitation of natural resources, and urban traffic.  There is evidence that workers in developing countries are exposed to noise levels well above occupational threshold set in developed countries. This may be due to ignorance towards preventive aspects of the health problem both on employee and employers part.  Occupational noise exposure and NIHL have been recognized as a problem among workers in Indian industries. The major industries in India are in the manufacturing sector. In an observational study by Singh et al., over 90% of workers engaged in various processes of casting and forging industry showed hearing loss in the noise-sensitive frequency range. Occupation was significantly associated with NIHL, and hearing loss was particularly high among the workers of forging section of small and medium enterprise iron and steel industries.  Apart from manufacturing industry workers, other group with specific professions such as soldiers, musicians, pilots, school and hospital staff, stone crushing industry is also the victims of NIHL. ,
In various studies factors such as age, gender, hypertension, serum cholesterol, smoking and diseases like diabetes mellitus and hypothyroidism were found to contribute hearing loss either as independent variable or in association with noise. In some observational studies the synergistic effect of smoking, noise exposure and age on hearing loss due to possible ototoxic substances in the chemical composition of mainstream smoke in combination with noise exposure and senile degeneration changes were observed. ,
To assess hearing loss in most of the previous studies pure tone audiometry (PTA) that may have subjectively biased results and hence interpretation, were used. ,,,, Very few studies have adopted brainstem evoked response audiometry (BERA) to assess hearing loss and auditory pathway affection whether central or peripheral. BERA rules out any subjective recording of hearing threshold. Further, it has the advantage of assessing the auditory pathway from distal cochlear nerve to the inferior colliculus. Thus, BERA can objectively assess whether central or only peripheral component of the auditory pathway is involved in NIHL. Previous studies could not reach a consensus about level of auditory pathway involvement whether central or peripheral in NIHL using BERA. , Thus auditory evaluation of occupational hearing loss using BERA remains less explored domain although it is a more objective diagnostic test than PTA. With above background, researchers explored the involvement of the auditory pathway among workers involved in stone cutting task at a construction site in central Gujarat with the following specific objectives:
- To determine BERA threshold (dB) in above noise-exposed category of workers
- To find out prevalence of NIHL and categorize it into normal, mild, moderate, moderately severe, severe and profound
- To assess BERA waveforms to establish whether involvement of the auditory pathway is central or peripheral.
| Materials and Methods|| |
Present cross-sectional study was conducted under STS Program 2013 after its approval by Indian Council of Medical Research. Duration of study was May 2013 to June 2013 in Clinical Neurophysiology Laboratory at a medical teaching institute in central Gujarat. Study was approved by Institutional Human Ethics Committee. Written informed consent was taken in the vernacular language structured format from all the participants, and the study was carried out in accordance with the World Medical Association Declaration of Helsinki.
Selection of participants
Totally 31 workers engaged in stone cutting task at construction site were selected to participate in the study. All the participants were pretested through a questionnaire designed by an ENT surgeon that included noise exposure, working hours, use of protective equipments and hearing loss, etc., and information was assessed. Interview was conducted by investigators in Gujarati and Hindi language. Sources of noise were those generated from electric-powered heavy-duty engines to which cutter was connected, and noise produced during cutting of stones in workplace. Noise exposure data for the participants in study group was obtained from the work safety and engineering staff of the construction company and was verified using the sound level meter manufactured by Recorders and Medicare Systems Chandigarh India. OSHA norms for hearing conservation were incorporated including an exchange rate of 5 dB (A), criterion level at 90 dB (A), criterion time of eight hours, threshold level equal to 80 dB (A), upper limit equal to 140 dB (A), and with F/S response rate.  In addition, the noise exposure was measured using Noise Pro DLX-1 ANSI SI.25-1991-Personal Noise Dosimeter.
After assessment through questionnaire, participants both cases and control underwent thorough history taking, clinical and otological examination provided in a structured format.
Thirty-one cases in the age group 21-55 with mean and SD 28 ± 8.9 years with exposure to noise >85 dB at workplace were included in the study.
Thirty age and sex matched participants in age group 21-45 with a mean age and SD 26 ± 8 years without exposures to noise were selected as a control.
Cases and controls with H/O hypertension, diabetes, hypothyroidism, musculoskeletal disorders, neuromuscular disorders, developmental disorders, facial asymmetry, ototoxic drugs intake, etc., were excluded from the study.
| Recording of Brainstem Evoked Response Audiometry|| |
After selecting the subjects and controls (through proper history and clinical examination), they were subjected to BERA testing according to standard techniques on RMS Portable Aleron EP-Electromyograph machine manufactured by RMS Recorders and Medicare System Chandigarh, India. Recording of BERA was carried out in a quiet and dimly lit room with the subject in the supine position. Subjects were briefly informed about the procedure. Restless, irritable and apprehensive subjects were allowed to relax for 5-10 min before testing. Surface electrodes were placed at the vertex (CZ), both ear lobes (Ai and Ac) and forehead (ground). Monaural auditory stimulus consisting of rarefaction clicks of 100 μ second square pulse were delivered through an electrically shielded earphone at a rate of 11.1/s. Contralateral ear was masked with pure white noise 30 dB below that of the BERA stimulus. A bandpass of 10-3000 Hz was used to filter out undesirable frequencies in the surrounding. Responses to 2000 click presentations were live averaged to obtain a single BERA waveform pattern. Waveforms were obtained at 25 dB, 40 dB, 60 dB and 90 dB in each ear. Waveforms obtained at 90 dB were used for data analysis. BERA threshold was marked when V waveform appeared in the recording on earliest sound intensity in dB. Cases were further classified into mild, moderate, severe and profound sensorineural hearing loss based on BERA threshold
Parameters under study
Brainstem evoked response audiometry threshold for each ear and absolute peak latencies of waves I, III, V, inter-peak latencies (IPLs) of I-III, III-V, I-V wave forms and V: I ratio were considered for assessment among study and control groups.
Mean ± SD for all BERA waveforms latencies and latency differences (ms) and V/I ratio (%) were compared between study and control groups using "unpaired Student t-test". Level of statistical significance was set at P < 0.05. Mode values for BERA threshold (dB) among cases and controls were obtained by choosing most repeating value in the data.
| Results and Observations|| |
In the present cross-sectional study, we collected data from 31 cases (Group 1) involved in stone cutting at a construction site in central Gujarat. Data were also collected from thirty participants with age; height and weight match (Group 2). [Table 1] shows the anthropometric and demographic features of both groups under study.
Thirty-one cases of mean age, height, weight and head circumference 28, 167, 56.8 and 55 respectively and 30 controls of mean age, height, and weight and head circumference 26, 169.2, 58.5 and 55.5 respectively were compared in the study. None of the general features in [Table 1], when compared using unpaired Student's t-test showed any statistical significance, i.e. P > 0.05. It suggests that general confounders were taken care of while doing the study.
Absolute peak BERA waveform latencies I, III and V were compared using unpaired students t-test between group 1 and group 2 as mentioned in [Table 2]. Comparison was done separately for left and right sides to avoid inter-eye bias. We observed statistically significant difference (P < 0.05) between absolute peak latencies of waveform I, III and V on the left side among Group 1 and Group 2. BERA latencies in Group 1 cases showed higher mean values on the left side. We also observed statistically significant difference (P < 0.05) between absolute peak latency of waveform I on the right side among Group 1 and Group 2 participants. No evidence of statistically significant difference (P > 0.05) between BERA latencies of waveform III and V on the right side among Group 1 and 2 was observed.
|Table 2: Comparison of absolute peak BERA waveforms between cases and controls |
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[Table 3] shows a comparison of IPL differences of waveform I-III, I-V and III-V among control and cases. We observed that none of the IPL differences was significantly different when compared between Group 1 and Group 2 participants (P > 0.05). BERA waveform V/I amplitude ratio was also statistically non-significant between group 1 and group 2.
|Table 3: Comparison of I-III, I-V, III-V latency difference and V/I amplitude ratio between cases and controls |
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Graph 1 shows the mean latencies of absolute peak BERA waveform I, III, V among cases and controls in left ear. Prolonged mean latencies were observed in above BERA waveforms among Group 1 participants when compared to Group 2.
[Table 4] shows BERA threshold for cases and controls. Mode value observed in Group 1 is higher than Group 2.
|Table 4: Mode values of BERA threshold among cases (Group 1) and controls (Group 2) |
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Out of 31 cases, mild hearing loss was observed in 7 cases, and moderate hearing loss in 24 cases. [Table 5] shows the severity of hearing loss in participants exposed to stone cutting task.
To summarize the results, we observed prolonged absolute peak BERA waveform I, III and V latencies among stone cutting workers with normal IPL differences. We further observed that BERA threshold was higher among this population with mild to moderate hearing loss when compared to control population.
| Discussion|| |
Occupational NIHL continues to haunt Indian manufacturing sector of small and medium enterprises. Many nonmanufacturing domains with specific professions also have been victims of NIHL. Experimental studies show involvement of neural structures in NIHL, probably secondary to hair cell degeneration and/or consequent to neural hyper-responsiveness by the excess of acoustic stimulation. ,, Many authors used BERA to study whether or not there are evidences of neural involvement in NIHL individuals, but the results observed were different because of the study methods and the sample profile. ,
Brainstem evoked response audiometry is useful in delineating the level of lesions in the auditory pathway from receptor (cochlea) to cortex. Any structural or functional change in the auditory pathway may lead to abnormal BERA results. Depending on abnormalities of absolute peak latencies and IPL differences, different abnormalities of BERA have been classified as sensory, neural and sensory-neural. Abnormality is labeled as sensory or cochlear if waveform I is absent or prolonged with normal IPL difference and other waves. Neural abnormality if, wave I is normal and remaining latency and IPL differences prolonged and sensory-neural if all parameters are involved.  The present study assessed alterations in BERA to evaluate auditory pathway in a homogeneous population involved in stone cutting task exposed to similar sound intensities for more than 1 year with age below 40 years.
We observed statistically significant prolongation of absolute peak wave BERA latencies I, III and V without any significant alteration in the IPL differences, obtained from left ear of exposed subjects. We also observed statistically significant prolongation of BERA wave I latency with unaltered other latencies and IPL differences on right ear of exposed subjects. Further, non-significant difference in wave V/I ratio was noted. All these findings suggest that there was involvement of sensory or cochlear component in both ears auditory pathway, and neural and retro-neural stations remained normal. Prolongation of latencies III and V on the left side could not be labeled as neural with normal IPL differences. With higher mode value of BERA threshold among these subjects (60 dB) when compared to controls (40 dB) we can conclude that stone cutting workers are at higher risk of developing NIHL with early involvement of peripheral/sensory/cochlear component of auditory pathway.
Present study is in agreement with Attias et al. Authors did a prospective study of the changes in BEAP traces in 10 male machine operators exposed to noise >112 dB for eight hours daily, during 14 months and observed that there were modifications in the absolute latencies of the early waves; however, without significant influence on central neural conduction.  Few studies in patients with NIHL have observed a significant prolongation of the latencies I, III, V with IPL I-III or I-V prolongation. These findings led them to conclusion that along with cochlear damage neuronal pathways in brainstem were also involved. ,, Differences between previous studies and present one may be due differences in selection of cases. In the present study, we selected cases with duration of exposure to noise with more than 1 year, whereas previous studies selected cases with more than 5 years exposure to noise.
Noise-induced hearing loss is usually bilateral and symmetrical affecting higher frequencies early and lower frequencies later.  Many factors might have contributed to the development of NIHL in stone cutting workers. Apart from noise arising from machine, its engine, and stone cutting; several other factors like lack of awareness about protective measures, duration of exposure for more than allotted hours may have contributed to development of NIHL in cases studied. Kitcher et al. reported higher prevalence of early NIHL in left ear of stone crushing workers in Ghana. Fernandes et al. also reported a higher NIHL prevalence in the left ears of urban bus drivers.  This suggests that lateralization of hearing loss is evident in occupational NIHL. In the present study, we observed higher BERA abnormalities in left ear. This may be attributed to the fact that engines of machines used for cutting purpose were positioned on the left side of the workers.
| Conclusion|| |
The present study evaluated hazardous effects of noise in stone cutting male workers with more than 1 year exposure and age <40 years at a construction site in central Gujarat. Mild to moderate hearing loss was observed in study population. Peripheral/cochlear component of auditory pathway was affected. Left ear was affected more than right side.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]