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Abstract

Noise, the 'unwanted sound', is now realised as one of the most important environmental hazard in the present day industrial world. Exposure to noise is imminent, spearheaded by man's casual attitude and ignorance of its effects. Thus, the indiscriminate hooting of horns and shrieking of loudspeakers continue unabated and disturb man's peace and tranquility. Noise leads to impaired hearing and causes general stress resulting in rise of blood pressure, enhanced sweating, muscle cramps, changes in cardiac functions and biorhythm, and increase in blood cortisol and cholesterol. Defence Institute of Physiology & Allied Sciences (DIPAS), DRDO, has been working towards combating noise pollution for over the last four decades for both the Defence Forces and for the civilians. In the Armed Forces, personnel are exposed to noise resulting from arms and ammunitions, gun and artillery firings, movement of heavy armoured vehicles, flying of aircraft and helicopters, engine rooms of naval ships and submarines etc. The high level of noise experienced by the personnel in their working environment is responsible for impairment in hearing functions and liable to trigger adverse reactions in extra-auditory systems. The auditory effects of noise directly influence the peripheral auditory system and the hearing function. Noise encountered by man in his occupational environment could be either loud or impulsive, of short intermittent duration or continuous noise of mixed intensities over a prolonged period. It acts as a biological stressor which results in various non-auditory system responses, leading to physiological and psychological stress. Researches on physiological and psychological effects and on performance and comfort have provided an extensive technology pool that serves as the basis of exposure guidelines, criteria and standards. Controlling noise and safeguarding hearing are important environmental issues that need to be addressed with care. The ill effects of noise on the auditory system may be alleviated by adequate hearing protection with the use of appropriate ear defenders, electronic noise reducing head sets, inhalation of carbogen (gas mixture of 5% CO2 and 95% O2), supplementation with antioxidants and restricted working time in noise environment as per the laid down environmental safety guidelines. These and other management techniques including use of musical sounds may also be useful in coping with the extra auditory effects of noise.

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Book on noise effects on man covering audiometry, aural reflex, hearing damage risk, physiological responses, motor performance and speech communication
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Article
The study was carried out in 200 male volunteers. They were divided into two groups. The study group was exposed to noise levels of more than 80 dB(A) for more than 8 hours a day for a period of 6 months, working in the steel and hammer industry, whereas the control group was working under normal conditions. The mean age of subjects was 33.33 + 0.867 years and the mean noise level to which they were exposed was 90.34 + 0.781 dB(A). Various autonomic function tests were carried out in both the groups and results were analyzed using Z test. Heart rate was recorded on cardiofax ECG machine and blood pressure (BP) was recorded using sphygmomanometer. The tests depicted significant increase in the mean resting heart rate and the heart rate response to standing (P=0.000), 30:15 ratio (P=0.002), the valsalva ratio (P=0.017), the % change in diastolic BP response to standing (P=0.000) and valsalva maneuver (P=0.000), the systolic BP and diastolic BP after cold pressor test (P=0.000) in study group as compared to the control group. The significant higher results in study group may be attributed to increased sympathetic activity. Thus, noise presents as a significant health hazard. It is recommended that maximum allowable duration of exposure should be reviewed and strictly followed.
Article
Workers in industries with impact noise, as well as soldiers exposed to supersonic blasts from armament and explosive devices, appear to be more at risk for hearing loss than are their counterparts exposed to continuous noise. Alternative considerations for hearing protection are dictated because of a disproportionately increased biophysical response in comparison to continuous noise. Impulse noise is a significant and distinct problem that requires a new strategy for hearing protection. A review of current clinical and occupational literature suggests that impulse noise may be more damaging than continuous sound. Statistical measurements such as kurtosis hold promise for the quantitative prediction of hearing loss. As sound energy to the cell increases, the mechanism of cochlear damage shifts from biochemical injury to mechanical injury. Outer hair cells appear to be more sensitive than inner hair cells to impulse noise because of their energy requirements, which lead to increased production of reactive oxygen and nitrogen species and self-destruction by apoptosis. Hearing protective devices currently in use for impulse noise include hunters' hearing devices, active noise-reduction headsets, and various in-ear plugs, including nonlinear reacting inserts. Existing equipment is hampered by the materials used and by present-day electronic technology. Antioxidants administered before sound exposure show promise in mitigating hearing loss in industrial and combat situations. New materials with improved damping, reflective, and absorption characteristics are required. Hearing protective devices that allow passage of ambient sound while blocking harmful noise might improve the compliance and safety of those exposed. Sensing devices that instantaneously and selectively hyperpolarize outer hair cells are discussed as alternate protection.
Six groups of chinchillas were used. Each exposure group contained five animals. The animals were made monaural onaural by surgically destroying the left cochlea and the animal was then prepared for auditory evoked response recording by implanting a dural electrode over the tentorium. There is a consistent, orderly relationship between the level of impulse superimposed on the continuous noise and the audiologic and histologic effects. The interaction effects between an impulse and continuous noise which individually are deemed as being safe, adds a further complication to the development of noise standards.
Article
Influence of noise spectra on auditory frequencies of 131 audiometrically normal human volunteers was assessed. Each subject was exposed to four different types of noise on different days for a period of 30 min. Noises utilized in this study were broadband noise (100 dBA), broadband noise (BBN) mixed independently with tones of 0.5, 1.2 and 4 kHz at three intensity levels (85, 95 and 105 dBA) and noises of different bandwidths (100 dBA) around the above tones as centre frequencies. BBN produced maximum TTS2 at 4 kHz (21.42 +/- 0.61 to 26.15 +/- 1.00 dB), while concentration of sound energy around these tones, affected hearing at one-half octave above the point of concentration of sound energy. TTS2 produced by 4 kHz tonal component of 95 and 105 dBA and 2 kHz of 105 dBA were significantly higher than the one produced by BBN at 4 kHz. The single tones of 2 and 4 kHz and noise of 1/3rd octave bandwidth (cf 4 kHz) produced TTS2s which were significantly higher as compared to that of BBN at 4 kHz. At the same centre frequency, noise concentrated in thinner bands was more injurious than that in the thicker bands. Lower frequencies of hearing appears to be more resistant to noise as for the same sound pressure level the TTS2 observed in low frequencies was less as compared to higher frequencies.
Article
The therapeutic role of carbogen was evaluated in subjects with sensorineural hearing loss by administering carbogen, a gas mixture of 95 per cent O2 and 5 per cent CO2, for seven consecutive days (30 min/day) and monitoring puretone audiometry before and after the administration. Significant improvement was observed both in air and bone conduction threshold levels on seventh day, indicating that there was some recoverable portion in the hearing level of these subjects. The improvement in hearing may be due to action of CO2 as an otic vasodilator coupled with supplementation of the O2 requirement of degenerating hair cells. Carbogen thus appears to be useful in persons with impaired hearing, involving the inner ear.
Article
A cross-sectional epidemiological survey was carried out in a car-body workshop involving 234 workers divided into three groups according to age and noise exposure duration. Their hearing levels, determined by using a standardized audiometric testing procedure, were compared to those of a reference population not exposed to noise, to those of a population exposed to quasisteady noises at 95 dB(A), and also to ISO 1999-1987. Results reveal significant hearing loss after 9 years of exposure, greater than that from quasisteady noise exposure with the same equivalent continuous A-weighted sound-pressure level.
Article
An analysis is made of data from a number of field investigations concerning the influence of steady‐state broad‐band noise on the hearing of workers, exposed to it continuously for eight hours a day. The results relate to exposure times ranging from 10 to 40 years and to noise with noise‐rating numbers for 500 to 2000 Hz (NR) ranging from 75 to 98 or sound levels from 80 to 103 dBA. Noise‐induced shifts of the median hearing levels as well as shifts indicated at the 90th, 75th, 25th, and 10th percentiles, were determined for seven frequencies between 500 and 8000 Hz as a function of exposure years and sound level. The variability in hearing levels associated with noise exposure was shown to be constant after ten exposure years and an increasing function of sound level at each frequency except 4000 Hz. At this frequency, the variance in hearing levels decreased with increasing sound level. The limit of permissible noise exposure, defined as the maximal level which did not cause measurable noise‐induced shift in hearing levels of workers exposed to it irrespective of exposure years, was shown to be NR 75 or 80 dBA. An acknowledgment is made of the need for hearing‐conservation measures given exposure conditions which exceed 80 dBA.
Article
8 Males (in their twenties) with normal ears were exposed to steady state noise, (broad band noise, 90 dB), impact noise with a frequency of once per 2 sec (peak value 105 dB, with about 25 msec B duration and peak value 120 dB with 25 msec and about 100 msec B duration), and a combination of steady state noise and impact noises. Impact noise alone, with peak value 105 dB, produced no significant temporary threshold shift (TTS) due to steady state noise or combined noise above both. TTS due to combined noise with impact noise (peak value 120 dB, B duration about 25 msec) and steady state noise were larger than that due to steady state noise alone, and the difference was statistically significant. In the case of third impact noise (peak value 120 dB, B duration 100 msec), the effect on hearing loss was as follows: impact noise alone > combined both > steady state noise.
Article
Continuous and impulse noises were combined to model more realistic noise environments. Monaural chinchillas were exposed to one of the following conditions: 50 impulses with 40 μsec A duration at 158 dB SPL peak pressure, 1/min; 95 dB SPL continuous noise at 2-4 kHz for 1 hr; superimposed combination of the continuous and impulse noise; 50 impulses with a 40 μsec A duration at 175 dB SPL peak pressure, 1/min; and interrupted combination of the continuous and impulse noise with the continuous noise off for 2 sec during the impulse delivery. Quiet thresholds were measured before and after exposure using the auditory evoked response and histology was obtained using the surface preparation technique. The audiometric and histological findings agree in showing that the superimposed combination of two noise exposures, shown to be safe for the chinchilla, produces traumatic effects which more than exceed the additive effects of either component. The existing damage risk criteria do not provide guidelines for such noise combinations.
Article
Summary 7 audiometrically normal, male students were exposed to a steady state noise S of 98 dBA and 2 steady state-impulse combined noises A and B (steady state component of 97 dBA, hammer noise 102 dBA and air exhaustion noise of 118 or 110 dBA) for 40–60 min. The regression line of temporary threshold shift (TTS) growth due to noise A on exposure duration was significantly steeper than that due to noise B. Both the lines were steeper than that due to noise S. The reason of the relatively larger effects of the noises A and B as compared with noise S could be explained by the fact that the noise S did not contain impulse components, because the octave band level at center frequency of 3 kHz of the noise S was roughly equal to that of the steady state noise component of noise A or B. The relatively larger effect of the noise A than B might be attributed mainly to the air exhaustion noise. It was suggested that the effect of a steady state noise on hearing might be additive to that of an impulse noise. The trend relationship between TTS during recovery and recovery time was nearly the same with the 3 noises.
Article
Temporary threshold shifts (ITS) in pure tone hearingacuity are reported for 15 subjects exposed in separate 15‐min periods to taped impact sounds [played back at 124‐ to 127 dB peak sound‐pressure level (SPL)], to three levels of filtered (75‐ tn 1200 cps) steady‐state noise (90, 100, 110 dB SPL), and to combinations of the recorded impact sounds with each level of the steady‐state noise.TTS&apos;s from all such exposures were typically small, with the largest shifts occurring in the 1000‐ to 3000 cps frequency range. When combined with 90‐ and 100 dB steady‐state noise, the impacts caused less threshold shift than when presented alone. Such TTS reductions were believed due to the relatively greater ability of the steady‐state noise to arouse and sustain the acoustic reflex with its consequent sound‐attenuationeffect. The addition of the 110 dB steady‐state noise did not induce a similar result quite possibly because this exposure, by itself, caused threshold shifts equal to or exceeding those of the impact sounds. More‐effective stimulation of the acoustic reflex was believed responsible for findings showing less TTS for combined impact/steady state noise than from exposure to just the steady‐state component of the combination. Indirect measures of acoustic‐reflex response [contralateral remote masking (CRM)] generally indicated that those ears with a strong reflex response show less noise‐induced shift. Correlations between TTS from impact and from steady‐state noise for the subject group indicated some degree of positive correspondence limited to frequencies of of 2000 cps and below and strongest for those subjects with a poor reflex response as shown by their CRM data.
Article
A-weighted equivalent continuous noise levels for hammer and press operations in a drop-forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A-weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long-term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop-forging industry are as great or greater than those resulting from continuous noise.
Article
This work was an attempt to characterize the various types of noise impulses in terms of their excitation mechanisms. It also studied how impulse noise affects the Leq, on the basis of measurements made at a number of workplaces. The paper concludes with a review of the incidence of hearing damage among groups of personnel exposed to different types of noise in the building industry.
Article
Audiometry was carried out in 130 weavers exposed to a continuous noise level of 102 dBA to 104 dBA. While audiograms were obtained for all the weavers at the pre-exposure level, 70 of them had undergone audiometric testing after 4 and 8 hr of exposure, for assessment of threshold shifts. Almost all the weavers, irrespective of age and length of exposure to occupational noise, suffered hearing loss at frequencies from 3000 Hz through other frequencies up to 8000 Hz, with a remarkable loss at 4000 Hz. Threshold shifts were only marginal. Control measures for noise reduction have been suggested.
Article
Certain individuals, such as police officers, are exposed to traumatic events as part of their occupational roles. In an effort to prevent psychological illnesses, notably the post-traumatic stress disorder, from arising out of work-related traumatic incidents, psychological interventions have been developed such as Critical Incident Stress Debriefing (Mitchell, 1983; Mitchell & Everly, 1996). The present study tests the hypothesis that debriefing reduces the psychological morbidity caused by work-related incidents. Because debriefing techniques were not designed for application on a 'one-off' basis (Robinson & Mitchell, 1993), the procedure studied here consisted of three successive debriefing sessions (at 24 hours, 1 month and 3 months post-trauma), which included traumatic stress education. In a sample of 243 traumatized police officers, a subgroup of debriefed officers (N = 86) was compared with non-debriefed internal (N = 82) and external (N = 75) control groups. No differences in psychological morbidity were found between the groups at pre-test, at 24 hours or at 6 months post-trauma. One week post-trauma, debriefed subjects exhibited significantly more post-traumatic stress disorder symptomatology than non-debriefed subjects. High levels of satisfaction with debriefing were not reflected in positive outcomes. The findings are translated into recommendations for the future use of debriefing in police practice.
Article
Some children with learning problems (LP) experience speech-sound perception deficits that worsen in background noise. The first goal was to determine whether these impairments are associated with abnormal neurophysiologic representation of speech features in noise reflected at brain-stem and cortical levels. The second goal was to examine the perceptual and neurophysiological benefits provided to an impaired system by acoustic cue enhancements. Behavioral speech perception measures (just noticeable difference scores), auditory brain-stem responses, frequency-following responses and cortical-evoked potentials (P1, N1, P1', N1') were studied in a group of LP children and compared to responses in normal children. We report abnormalities in the fundamental sensory representation of sound at brain-stem and cortical levels in the LP children when speech sounds were presented in noise, but not in quiet. Specifically, the neurophysiologic responses from these LP children displayed a different spectral pattern and lacked precision in the neural representation of key stimulus features. Cue enhancement benefited both behavioral and neurophysiological responses. Overall, these findings contribute to our understanding of the preconscious biological processes underlying perception deficits and may assist in the design of effective intervention strategies.
Article
The auditory system is permanently open - even during sleep. Its quick and overshooting excitations caused by noise signals are subcortically connected via the amygdala to the hypothalamic-pituitary-adrenal-axis (HPA-axis). Thus noise causes the release of different stress hormones (e.g. corticotropin releasing hormone: CRH; adrenocorticotropic hormone: ACTH) especially in sleeping persons during the vagotropic night/early morning phase. These effects occur below the waking threshold of noise and are mainly without mental control. Animal experiments show noise-induced changes in sensitivity of cellular cortisol receptors by increase of heat-shock proteins, and ultrastructural changes in the tissue of the heart and the adrenal gland. Increased cortisol levels have been found in humans when exposed to aircraft noise or road traffic noise during sleep. The effects of longer-lasting activation of the HPA-axis, especially long term increase of cortisol, are manifold: immuno suppression (e.g. eosinopenia), insulin resistance (e.g. diabetes), cardiovascular diseases (e.g. hypertension and arteriosclerosis), catabolism (e.g. ostoeporosis), intestinal problems (e.g. stress ulcer) etc. Even worse may be the widespread extrahypothalamical effects of CRH/and/or ACTH which have the potential to influence nearly all regulatory systems, causing for example stress-dysmenorrhea etc. as signs of disturbed hormonal balance.
Article
Noise is one of the commonest physical stressors to which industrial workers are exposed. Many workers complain of symptoms associated with a non-specific generalized stress response, including disturbed sleep. However, industrial workers may be exposed to more than one source of stress and it is not possible to completely attribute the disturbed nocturnal sleep and changes in heart rate to the effects of loud noise alone. This study was done to find out whether acute exposure of healthy individuals to loud occupational noise during the daytime would cause changes in their nocturnal sleep architecture, heart rate during sleep and serum cortisol levels. Baseline polysomnography was done on ten subjects who were exposed for eight hours either to continuous occupational background noise levels of >75dB(A), or a quiet environment. Sleep polysomnography was done on the night prior to and after exposure. Blood was collected for serum cortisol estimation at night prior to sleep and in the morning after waking up. Statistical analysis was done by repeated measures ANOVA with Tukey's post test. The sleep efficiency was less than 80% and the total time spent in Rapid Eye Movement (REM) sleep, Slow Wave Sleep (SWS) and the REM onset latency were significantly decreased on the night after exposure to noise. There was a significant increase in stage shifts. The percentage fall in heart rate during sleep was decreased compared to the baseline values. The serum cortisol levels in the morning after exposure to noise was significantly increased. Workers exposed to loud background occupational noise react to the stress and show changes in nocturnal sleep architecture and heart rate which may be contributed to the exposure to noise.
Article
The association of aircraft noise exposure with cognitive performance was examined by means of a cross-sectional field survey. Two hundred thirty six children attending 10 primary schools around Heathrow Airport in west London were tested on reading comprehension, immediate/delayed recall and sustained attention. In order to obtain the information about their background, a questionnaire was delivered to the parents and 163 answers were collected. Logistic regression models were used to assess performance on the cognitive tests in relation to aircraft noise exposure at home and possible individual and school level confounding factors. A significant dose-response relationship was found between aircraft noise exposure at home and performance on memory tests of immediate/delayed recall. However there was no strong association with the other cognitive outcomes. These results suggest that aircraft noise exposure at home may affect children's memory.
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