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   Table of Contents - Current issue
January-February 2017
Volume 19 | Issue 86
Page Nos. 1-40

Online since Tuesday, January 31, 2017

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Using Auditory Steady-State Responses for Measuring Hearing Protector Attenuation p. 1
Olivier Valentin, Sasha M John, Frédéric Laville
DOI:10.4103/1463-1741.199238  PMID:28164933
Introduction: Present methods of measuring the attenuation of hearing protection devices (HPDs) have limitations. Objective measurements such as field microphone in real-ear do not assess bone-conducted sound. Psychophysical measurements such as real-ear attenuation at threshold (REAT) are biased due to the low frequency masking effects from test subjects’ physiological noise and the variability of measurements based on subjective responses. An auditory steady-state responses (ASSRs) procedure is explored as a technique which might overcome these limitations. Subjects and Methods: Pure tone stimuli (500 and 1000 Hz), amplitude modulated at 40 Hz, are presented to 10 normal-hearing adults through headphones at three levels in 10 dB steps. Two conditions were assessed: unoccluded ear canal and occluded ear canal. ASSR amplitude data as a function of the stimulation level are linearized using least-square regressions. The “physiological attenuation” is then calculated as the average difference between the two measurements. The technical feasibility of measuring earplug attenuation is demonstrated for the group average attenuation across subjects. Results: No significant statistical difference is found between the average REAT attenuation and the average ASSR-based attenuation. Conclusion: Feasibility is not yet demonstrated for individual subjects since differences between the estimates occurred for some subjects.
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Epidemiology and Risk Factors for Leisure Noise-Induced Hearing Damage in Flemish Young Adults p. 10
Sofie Degeest, Els Clays, Paul Corthals, Hannah Keppler
DOI:10.4103/1463-1741.199241  PMID:28164934
Context: Young people regularly expose themselves to leisure noise and are at risk for acquiring hearing damage. Aims: The objective of this study was to compare young adults’ hearing status in relation to sociodemographic variables, leisure noise exposure and attitudes and beliefs towards noise. Settings and Design: A self-administered questionnaire regarding hearing, the amount of leisure noise exposure and attitudes towards noise and hearing protection as well as an audiological test battery were completed. Five hundred and seventeen subjects between 18 and 30 years were included. Subject and Methods: Hearing was evaluated using conventional audiometry, transient evoked and distortion product otoacoustic emissions. On the basis of their hearing status, participants were categorised into normal hearing, sub-clinical or clinical hearing loss. Statistical Analysis Used: Independent samples t-tests, chi-square tests and multiple regression models were used to evaluate the relation between groups based on hearing status, sociodemographics, leisure noise and attitudes towards noise. Results: Age was significantly related to hearing status. Although, the subjects in this study frequently participated in leisure activities, no significant associations between leisure noise exposure and hearing status could be detected. No relation with subjects’ attitudes or the use of hearing protection devices was found. Conclusions: This study could not demonstrate clinically significant leisure noise-induced hearing damage, which may lead to more non-protective behaviour. However, the effects of leisure noise may become noticeable over a long-term use since age was found to be related with sub-clinical hearing loss. Longitudinal studies are needed to evaluate the long-term effects of noise exposure.
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Effect of Filters on the Noise Generated by Continuous Positive Airway Pressure Delivered via a Helmet p. 20
Ricardo Hernández-Molina, Francisco Fernández-Zacarías, Isabel Benavente-Fernández, Gema Jiménez-Gómez, Simón Lubián-López
DOI:10.4103/1463-1741.199237  PMID:28164935
Introduction: One of the problems that the delivery of continuous positive airway pressure (CPAP) via a helmet poses is the generation of noise. The objective of our study was to assess the effect that the use of filter has on sound pressure levels generated by the delivery of positive airway pressure at different gas flow rates. Materials and Methods: Sound pressure levels generated by neonatal helmet CPAP delivery were measured at different gas flows (20, 30, and 40 l/min) with and without a breathing filter. Noise intensity was measured by installing microphones in the inner ear of dummy heads wearing helmets. Results: The sound pressure level increased by 38% at a gas flow of 40 l/min, as compared to a gas flow of 20 l/min {74 dBA [interquartile range (IQR) 2,2] vs 52 dBA (IQR 5,9), respectively}. Using the breathing filter as a diffuser has a variety of effects on sound pressure levels according to the gas flow rate. Conclusion: The intensity of the noise generated by helmet delivery of positive airway pressure depends on the type of helmet used, gas flow, and use or not of a diffuser filter. Breathing filters with gas flows over 30 l/min might not be recommended since they would not attenuate but will rather amplify sound pressure.
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The Effects of Acoustic White Noise on the Rat Central Auditory System During the Fetal and Critical Neonatal Periods: A Stereological Study p. 24
Mohammad Saied Salehi, Mohammad Reza Namavar, Amin Tamadon, Raziyeh Bahmani, Mohammad Reza Jafarzadeh Shirazi, Homayoun Khazali, Leila Dargahi, Sareh Pandamooz, Farzad Mohammad-Rezazadeh, Fatemeh Sadat Rashidi
DOI:10.4103/1463-1741.199239  PMID:28164936
Aim: To evaluate the effects of long-term, moderate level noise exposure during crucial periods of rat infants on stereological parameters of medial geniculate body (MGB) and auditory cortex. Materials and Methods: Twenty-four male offspring of 12 pregnant rats were divided into four groups: fetal-to-critical period group, which were exposed to noise from the last 10 days of fetal life till postnatal day (PND) 29; fetal period group that exposed to noise during the last 10 days of fetal life; critical period group, exposed to noise from PND 15 till PND 29, and control group. White noise at 90 dB for 2 h per day was used. Statistical Analysis Used: Variance for variables was performed using Proc GLM followed by mean comparison by Duncan’s multiple range test. Results: Numerical density of neurons in MGB of fetal-to-critical period group was lower than control group. Similar results were seen in numerical density of neurons in layers IV and VI of auditory cortex. Furthermore, no significant difference was observed in the volume of auditory cortex among groups, and only MGB volume in fetal-to-critical period group was higher than other groups. Estimated total number of neurons in MGB was not significantly different among groups. Conclusion: It seems necessary to prevent long-term moderate level noise exposure during fetal-to-critical neonatal period.
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Classroom Listening Conditions in Indian Primary Schools: A Survey of Four Schools p. 31
Gayathri Sundaravadhanan, Heramba G Selvarajan, Bradley McPherson
DOI:10.4103/1463-1741.199240  PMID:28164937
Introduction: Background noise affects the listening environment inside classrooms, especially for younger children. High background noise level adversely affects not only student speech perception but also teacher vocal hygiene. The current study aimed to give an overview of the classroom listening conditions in selected government primary schools in India. Materials and Methods: Noise measurements were taken in 23 classrooms of four government primary schools in southern India, using a type 2 sound level meter. In each classroom measurements were taken in occupied and unoccupied conditions. Teacher voice level was measured in the same classrooms. In addition, the classroom acoustical conditions were observed and the reverberation time for each classroom was calculated. Results: The mean occupied noise level was 62.1 dBA and 65.6 dBC, and the mean unoccupied level was 62.2 dBA and 65 dBC. The mean unamplified teacher speech-to-noise ratio was 10.6 dBA. Both the occupied and unoccupied noise levels exceeded national and international recommended levels and the teacher speech-to-noise ratio was also found to be inadequate in most classrooms. The estimated reverberation time in all classrooms was greater than 2.6 seconds, which is almost double the duration of accepted standards. In addition, observation of classrooms revealed insufficient acoustical treatment to effectively reduce internal and external noise and minimize reverberation. Conclusion: The results of this study point out the need to improve the listening environment for children in government primary schools in India.
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