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PubMed2003

Prophylactic effect of Ca2+ -deficient artificial perilymph perfusion on noise-induced hearing loss.

OBJECTIVE: To investigate the prophylactic effect of low calcium concentration perilymph on noise-induced hearing loss. METHODS: Forty guinea pigs with normal hearing weighing 250-350 g were assigned to five groups (8 in each group): (1) Ca(2+)-deficient perilymph perfusion (CDP) for 2 h; (2) white noise (120 dB SPL) exposure (WNE) only for 1 h, (3) combination of calcium-deficient perilymph perfusion and white noise (120 dB SPL) exposure (WNE + CDP); (4) normal artificial perilymph (NAP) perfusion for 2 h; and (5) white noise exposure + normal artificial perilymph perfusion (WNE + NAP) for 2 h. Compound action potentials (CAP) evoked by click was recorded from round window every 15 min. The cochleae from 5 animals in each group were examined with scanning electron microscope. RESULTS: The CAP for group 1 experienced a threshold shift (TS) of 15-26 dB, while group 2 yielded a 46-59 dB TS and group 3 a 37-45 dB TS; no threshold shift occurred in group 4. The CAP TS in group 5 was 33-64 dB. The CAP TS of group 3 was less than that of group 2. After one hour of noise exposure, the CAP TS of group 3 were 45.92 +/- 2.90 dB and 59.30 +/- 3.95 dB in group 2. There were significant differences (P < 0.05) between groups 3 and 2. The CAP TS of group 3 was less than that of group 5 at the points of 1, 1.5 and 2 h after noise exposure. There was a significant difference between groups 3 and 5 (P < 0.01). Stereocilia of 89 OHC(3) were in disarray in five cochleae after noise exposure in group 2. The cuticular plates of 8 OHC(2),3 sank and the stereocilia became fused in only one animal cochlea after noise exposure in group 3 combined with low calcium perilymph perfusion. CONCLUSIONS: Low calcium concentration appears to participate in preventing noise-induced hearing loss and the rising of calcium concentrations in inner hair cells after noise exposure, which may have been due to the opening of calcium channels in inner hair cells during noise exposure. The mechanism of the prophylactic effect might be caused by a lower calcium concentration in inner hair cells in the cochlea attenuating the influence of noise exposure on hearing loss; calcium deficient perilymph perfusion prevented calcium accumulation in inner hair cells of the cochlea. The motility of the OHCs might be partially inhibited by low calcium concentration that reduced noise-induced hearing loss in turn.

Action Potentials↗
PubMed1981

[Studies on the activity level of the cerebral cortex by the noise exposure -- with regard to the function of maintaining concentration (TAF) and average auditory evoked response (AER) (author's transl)].

Subjects were exposured to two qualitatively different kind of noise (white noise and variable noise) with the same sound pressure of 90 phon for one hour as the mental stress. Changes of the function of maintaining concentration (TAF), flicker fusion (Ff), EEG and average auditory evoked response (AER) caused by this noise exposure were analyzed. The results obtained are as follows: 1) TAF-L and TAF-D of the white noise group after the exposure significantly lowered in comparison with the values before exposure, whereas in the variable noise group they tended to lower after the exposure. 2) FF of the both noise group significantly lowered after the exposure. 3) The difference in EEG before and after exposure was greater in the white noise group than in the variable noise group. 4) In analysis of variance on each frequency band of EEG during the exposure by group, a significant difference was observed between the two groups and it was noted that the exposure to white noise greatly affected the EEG. 5) The difference in N1 latency of AER before and after the exposure was greater in the white noise group than in the variable noise group. 6) In the white noise group, a significant correlation was observed between the lowering of TAF-L and the delay of N1 latency of AER. The present study on EEG and AER is further evidence of the accuracy of the function of maintaining concentration (TAF) in measuring the mental stress.

Adult↗
PubMed1997

Synergestic effects of noise and aminoglycoside antibiotic (gentamicin) on auditory function in the gerbil.

Exposure to excessive noise can cause auditory impairment in people as well as in animals, which can be aggravated by many different ototoxic substances, such as aminoglycosides. In the present study, the gerbil was selected as the experimental animal because the gerbil has low-frequency auditory sensitivity that is similar to human beings. Auditory function in gerbils upon exposure to noise and/or gentamicin was evaluated from non-invasive records of brainstem auditory evoked potentials (BAEPs). Fifty mature male Mongolian gerbils were divided randomly into four groups. The control group was exposed neither to noise nor to gentamicin. The noise group was exposed to 100dBA noise ten hours a day for four weeks. The gentamicin group was treated with one dose of gentamicin, 75 mg/Kg i.m., daily for four weeks. The noise + gentamicin group was exposed concurrently to both noise and gentamicin treatment. BAEPs were recorded from all gerbils 24 hours before any experimental treatment, then every week for eight consecutive weeks. Long-term exposure to noise and/or gentamicin treatment was found to reduce gerbil's body weight. The increase in auditory threshold upon concurrent exposure to both noise and gentamicin treatment (evaluated from BAEPs) exceeded the sum of effects caused by exposure to noise alone and to gentamicin alone. Although differences of peak or interpeak latencies among the four groups were not statistically significant, large standard deviations were noted in the noise+gentamicin group. Thus the apparent threshold shifts in gerbils indicated a major noise and/or gentamicin induced auditory impairment to the cochlea, and the slight latency variations probably suggested a minor injury to the auditory pathways. We emphasize that noise and aminoglycoside antibiotic gentamicin can cause damage to the hearing ability at the frequency range vital to human speech recognition, and their effects are synergetic.

Animals↗
PubMed1998

Informativeness of critical ratios "useful signal-masking noise" in speech communication.

In experimental conditions the influence of 8 ratios "useful signal-masking noise" of 3 types of production noise (impulse, continuous and interrupted) is studied as well as continuous (white) noise as control on the perception of an audiometric test by 60 individuals with normal hearing. The test is understandable phonetically with difficulties and balanced at speech. The test intensity is L(equiv).70-75 dB/A/. The most expressed masking effect of continuous (white) noise, followed by the impulse and constant production noise is found. The lowest masking effect is found out at interrupted noise. This is explained by the acoustic characteristics of exposed types of noise. The masking effect of noise is limited to a high degree by the parameter "signal-noise" ratio, which is confirmed by the found negative correlation relationship with percentage speech intelligibility. The critical ratios "signal-noise", characterized with sharp decline of the level of discrimination of speaking signal and deterioration of the effectiveness of speech communication are established. In this paper the problem for conforming the speech communication both with the intensity and acoustic characteristics of masking noise and with the "signal-noise" ratio is discussed. Besides this in the critical "useful signal-masking noise" ratios better individual achievements could be a criterion for professional selection of candidates for operators.

Adult↗
PubMed1999

Extinction risk and the 1/f family of noise models.

In order to predict extinction risk in the presence of reddened, or correlated, environmental variability, fluctuating parameters may be represented by the family of 1/f noises, a series of stochastic models with different levels of variation acting on different timescales. We compare the process of parameter estimation for three 1/f models (white, pink and brown noise) with each other, and with autoregressive noise models (which are not 1/f noises), using data from a model time-series (length, T) of population. We then calculate the expected increase in variance and the expected extinction risk for each model, and we use these to explore the implication of assuming an incorrect noise model. When parameterising these models, it is necessary to do so in terms of the measured ("sample") parameters rather than fundamental ("population") parameters. This is because these models are non-stationary: their parameters need not stabilize on measurement over long periods of time and are uniquely defined only over a specified "window" of timescales defined by a measurement process. We find that extinction forecasts can differ greatly between models, depending on the length, T, and the coefficient of variability, CV, of the time series used to parameterise the models, and on the length of time into the future which is to be projected. For the simplest possible models, ones with population itself the 1/f noise process, it is possible to predict the extinction risk based on CV of the observed time series. Our predictions, based on explicit formulae and on simulations, indicate that (a) for very short projection times relative to T, brown and pink noise models are usually optimistic relative to equivalent white noise model; (b) for projection timescales equal to and substantially greater than T, an equivalent brown or pink noise model usually predicts a greater extinction risk, unless CV is very large; and (c) except for very small values of CV, for timescales very much greater than T, the brown and pink models present a more optimistic picture than the white noise model. In most cases, a pink noise is intermediate between white and brown models. Thus, while reddening of environmental noise may increase the long-term extinction probability for stationary processes, this is not generally true for non-stationary processes, such as pink or brown noises.

Animals↗
PubMed2000

A wavelet-based method for improving signal-to-noise ratio and contrast in MR images.

Magnetic resonance (MR) images acquired with fast measurement often display poor signal-to-noise ratio (SNR) and contrast. With the advent of high temporal resolution imaging, there is a growing need to remove these noise artifacts. The noise in magnitude MR images is signal-dependent (Rician), whereas most de-noising algorithms assume additive Gaussian (white) noise. However, the Rician distribution only looks Gaussian at high SNR. Some recent work by Nowak employs a wavelet-based method for de-noising the square magnitude images, and explicitly takes into account the Rician nature of the noise distribution. In this article, we apply a wavelet de-noising algorithm directly to the complex image obtained as the Fourier transform of the raw k-space two-channel (real and imaginary) data. By retaining the complex image, we are able to de-noise not only magnitude images but also phase images. A multiscale (complex) wavelet-domain Wiener-type filter is derived. The algorithm preserves edges better when the Haar wavelet rather than smoother wavelets, such as those of Daubechies, are used. The algorithm was tested on a simulated image to which various levels of noise were added, on several EPI image sequences, each of different SNR, and on a pair of low SNR MR micro-images acquired using gradient echo and spin echo sequences. For the simulated data, the original image could be well recovered even for high values of noise (SNR approximately 0 dB), suggesting that the present algorithm may provide better recovery of the contrast than Nowak's method. The mean-square error, bias, and variance are computed for the simulated images. Over a range of amounts of added noise, the present method is shown to give smaller bias than when using a soft threshold, and smaller variance than a hard threshold; in general, it provides a better bias-variance balance than either hard or soft threshold methods. For the EPI (MR) images, contrast improvements of up to 8% (for SNR = 33 dB) were found. In general, the improvement in contrast was greater the lower the original SNR, for example, up to 50% contrast improvement for SNR of about 20 dB in micro-imaging. Applications of the algorithm to the segmentation of medical images, to micro-imaging and angiography (where the correct preservation of phase is important for flow encoding to be possible), as well as to de-noising time series of functional MR images, are discussed.

Algorithms↗
PubMed1992

[A recommendation for calibration and choice of masking noises used in speech audiometry].

Tests to evaluate speech recognition ability against background noise have still not been adequately standardized. This is due in part to the lack of a calibration procedure for the various noises used in testing. In the present study, a psychoacoustic method for the calibration of fluctuating background noises was evaluated. Three types of noise were used: babble noise, stationary noise and fluctuating speech simulating noise in accordance with (CCITT Rec. G 227). Following calibration, the masking effect of each type of noise was evaluated. Results indicated that stationary and fluctuating speech simulating noise had similar effect on speech understanding ability. The steepness of the intensity-intelligibility function was significantly greater using babble noise as compared with stationary or fluctuating speech simulating noise. Babble noise was well accepted by our subjects. However, since its measurement can be calibrated, stationary speech simulating noise may also be used in speech audiometry.

Adult↗
PubMed1996

Measurement of quantum noise in fluoroscopic systems for portal imaging.

In fluoroscopic portal imaging systems, a metal plate is bonded to a phosphor screen and together these act as the primary x-ray sensor. The light from the screen is collected and imaged by a lens on the target of a video camera. The demagnification (M) between the large area of the phosphor being imaged and the small active area of the video camera results in poor optical coupling between the screen and the video camera. Consequently x-ray quantum noise is small compared to other noise sources. By reducing the demagnification, the light from the screen is collected more efficiently, so we were able to increase the x-ray quantum noise relative to other noise sources and thus unambiguously identify it. The noise power spectrum was measured as a function of M to determine the relationship between the x-ray quantum noise. shot noise, and amplifier noise. It was found by extrapolation to clinical demagnifications that the amplifier noise dominates x-ray quantum noise, at all spatial frequencies, but the shot noise was less than the x-ray quantum noise at low spatial frequencies. For low spatial frequencies, this implies that a secondary quantum sink can be avoided. If amplifier noise could be sufficiently reduced, x-ray quantum limited images could be obtained in clinical systems at low spatial frequencies.

Equipment Design↗
PubMed2004

Detection and characterization of lesions on low-radiation-dose abdominal CT images postprocessed with noise reduction filters.

PURPOSE: To assess the effect of noise reduction filters on detection and characterization of lesions on low-radiation-dose abdominal computed tomographic (CT) images. MATERIALS AND METHODS: Low-dose CT images of abdominal lesions in 19 consecutive patients (11 women, eight men; age range, 32-78 years) were obtained at reduced tube currents (120-144 mAs). These baseline low-dose CT images were postprocessed with six noise reduction filters; the resulting postprocessed images were then randomly assorted with baseline images. Three radiologists performed independent evaluation of randomized images for presence, number, margins, attenuation, conspicuity, calcification, and enhancement of lesions, as well as image noise. Side-by-side comparison of baseline images with postprocessed images was performed by using a five-point scale for assessing lesion conspicuity and margins, image noise, beam hardening, and diagnostic acceptability. Quantitative noise and contrast-to-noise ratio were obtained for all liver lesions. Statistical analysis was performed by using the Wilcoxon signed rank test, Student t test, and kappa test of agreement. RESULTS: Significant reduction of noise was observed in images postprocessed with filter F compared with the noise in baseline nonfiltered images (P =.004). Although the number of lesions seen on baseline images and that seen on postprocessed images were identical, lesions were less conspicuous on postprocessed images than on baseline images. A decrease in quantitative image noise and contrast-to-noise ratio for liver lesions was noted with all noise reduction filters. There was good interobserver agreement (kappa = 0.7). CONCLUSION: Although the use of currently available noise reduction filters improves image noise and ameliorates beam-hardening artifacts at low-dose CT, such filters are limited by a compromise in lesion conspicuity and appearance in comparison with lesion conspicuity and appearance on baseline low-dose CT images.

Adult↗
PubMed2006

When response variability increases neural network robustness to synaptic noise.

Cortical sensory neurons are known to be highly variable, in the sense that responses evoked by identical stimuli often change dramatically from trial to trial. The origin of this variability is uncertain, but it is usually interpreted as detrimental noise that reduces the computational accuracy of neural circuits. Here we investigate the possibility that such response variability might in fact be beneficial, because it may partially compensate for a decrease in accuracy due to stochastic changes in the synaptic strengths of a network. We study the interplay between two kinds of noise, response (or neuronal) noise and synaptic noise, by analyzing their joint influence on the accuracy of neural networks trained to perform various tasks. We find an interesting, generic interaction: when fluctuations in the synaptic connections are proportional to their strengths (multiplicative noise), a certain amount of response noise in the input neurons can significantly improve network performance, compared to the same network without response noise. Performance is enhanced because response noise and multiplicative synaptic noise are in some ways equivalent. So if the algorithm used to find the optimal synaptic weights can take into account the variability of the model neurons, it can also take into account the variability of the synapses. Thus, the connection patterns generated with response noise are typically more resistant to synaptic degradation than those obtained without response noise. As a consequence of this interplay, if multiplicative synaptic noise is present, it is better to have response noise in the network than not to have it. These results are demonstrated analytically for the most basic network consisting of two input neurons and one output neuron performing a simple classification task, but computer simulations show that the phenomenon persists in a wide range of architectures, including recurrent (attractor) networks and sensorimotor networks that perform coordinate transformations. The results suggest that response variability could play an important dynamic role in networks that continuously learn.

Algorithms↗
PubMed1974

Free-operant escape-avoidance of noise by rats.

A series of experiments was conducted to establish free-operant escape-avoidance responding in rats using noise as the stimulus. Naive rats did not acquire a bar-press response on an escape-avoidance of noise schedule. Similarly, free-operant responding established using escape-avoidance of shock was not maintained when noise was substituted for shock. Noise stimuli of 110 dB did maintain responding, but at a lower level than during training, when the noise stimuli had first been paired with shock. Noise stimuli of 97 dB and 87 dB were not effective under those same conditions. Additional rats were trained on a free-operant escape-avoidance schedule of shock and then exposed to a delayed conditioning procedure in which noise was the conditioned stimulus and shock was the unconditioned stimulus. When these subjects were then tested with noise alone, two of the three subjects conditioned and tested with 105-dB noise displayed escape-avoidance of noise, but none of the rats conditioned and tested at 97 dB displayed escape-avoidance of noise. The results suggest that free-operant escape-avoidance of noise can be demonstrated; however, only higher intensity noise stimuli that have been paired with shock are effective.

Journal Article↗
PubMed2004

Effect of laryngoplasty on respiratory noise reduction in horses with laryngeal hemiplegia.

REASONS FOR PERFORMING STUDY: Laryngoplasty is the technique of choice for treatment of laryngeal hemiplegia, with the aim of improving airway function and/or eliminating respiratory noise. However, there are no quantitative data in the literature describing the effect of laryngoplasty on upper airway noise or its relationship to upper airway mechanics in horses with laryngeal hemiplegia. OBJECTIVES: To determine whether laryngoplasty reduces respiratory noise in exercising horses with laryngeal hemiplegia; and to establish whether the degree of upper airway obstruction can be predicted by upper airway noise, or the degree of arytenoid abduction correlated with airway obstruction and noise production. METHODS: Six Standardbred horses with normal upper airways during maximal exercise were used. Respiratory sounds and inspiratory transupper airway pressure (Pui) were measured in all horses before and after induction of laryngeal hemiplegia and 30, 60 and 90 days after laryngoplasty. Inspiratory sound level (SL) and the sound intensity of the 3 inspiratory formants (F1, F2 and F3, respectively) were measured using a computer-based sound analysis programme. The degree of abduction was graded by endoscopic visualisation 1, 30, 60 and 90 days post operatively. Linear regression analysis was used to determine correlations between Pui, sound indices and grades of arytenoid abduction. RESULTS: In laryngeal hemiplegia-affected horses, Pui, inspiratory SL and the sound intensity of F1, F2 and F3 were significantly increased. At 30 days following laryngoplasty, the sound intensity of F1 and Pui returned to baseline values. The sound intensities of F2, F3 and SL were significantly improved from laryngeal hemiplegia values at 30 days post operatively, but did not return to baseline at any measurement period. Sound level, F2 and F3 were significantly correlated with Pui (P<0.05), but the correlations were weak (r2 = 0.26, 035 and 0.40, respectively). Grade of abduction and F2 were positively and significantly correlated (P<0.006, r2 = 0.76). Grade of arytenoid abduction and Pui were not correlated (P = 0.12). CONCLUSIONS: Laryngoplasty reduced inspiratory noise in laryngeal hemiplegia-affected horses by 30 days following surgery, but did not return it to baseline values. While upper airway noise and Pui were correlated, this relationship was insufficiently strong to predict Pui from noise in individual animals. The degree of arytenoid abduction was not correlated with Pui, but was positively correlated with noise production. POTENTIAL RELEVANCE: Laryngoplasty reduces upper airway noise in horses with laryngeal hemiplegia, but is not as effective as bilateral ventriculocordectomy in this regard, although respiratory noise reduction occurs more rapidly than with bilateral ventriculocordectomy. Residual noise during exercise cannot be used as a predictor of improvement in upper airway function in individual horses following laryngoplasty. The degree of arytenoid abduction obtained following surgery does not affect upper airway flow mechanics. Interestingly, we found that the greater the arytenoid abduction, the louder the respiratory noise.

Animals↗
PubMed2001

The influence of psychological factors on self-reported physiological effects of noise.

We examine the possibility that physiological effects of noise may result not only from noise exposure per se, but also from people's beliefs about the noise. Due to widely publicised changes to the runway configuration at Sydney Airport, aircraft noise levels in nearby areas were expected to either increase, decrease or remain the same. As part of the Sydney Airport Health Study, residents in each of these 3 expected-change areas (N=1015) completed a structured interview which included indices of noise reaction (including annoyance) and physical and mental health, prior to the anticipated changes. Concurrent (pre-change) measures of aircraft noise levels were taken. Self-reported physiological/health effects differed across areas with the same aircraft noise level consistently with differences in psychological reaction across these areas. Expected change in noise level added to the level of self-reported physiological symptoms predicted by noise level in regression analyses. Dose-response functions differed across the expected-change areas. These results are consistent with the hypothesis that noise exposure produces physiological symptoms, but that expectations regarding future noise levels also contribute to the physiological impact of noise, which may be reduced by addressing psychosocial factors related to noise reaction.

Journal Article↗
PubMed1998

Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla.

Exposure to low level noise prior to a high level exposure reduces noise-induced hearing loss in mammals. This phenomenon is known as sound conditioning or 'toughening'. Reactive oxygen intermediates have been implicated in noise-induced cochlear damage. To evaluate if in situ antioxidant processes may play a role in the toughening phenomenon initiated by low level noise exposure we analyzed glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase in stria vascularis and organ of Corti fractions from cochleae of chinchillas exposed to a sound conditioning paradigm. Chinchillas were either (A) kept in quiet cages (control), (B) exposed to conditioning noise of a 0.5 kHz octave band (90 dB for 6 h/day for 10 days), (C) exposed to high level noise (105 dB for 4 h) or (D) exposed to conditioning noise (B) followed by exposure to the higher level noise (C). Each of the noise exposure conditions (B, C, D) induced changes in the levels of these three antioxidant enzymes. The enzyme-specific activity data for the four subject groups support the following two hypotheses. (1) Changes in glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase play a role in attenuating hearing loss associated with sound conditioning followed by high level noise. (2) Hair cells in the organ of Corti are protected from noise-induced damage by increasing stria vascularis levels of catalase, a hydrogen peroxide scavenging enzyme, and of enzymes involved in maintaining glutathione in the reduced state. The model formulated by these hypotheses suggests that agents that protect or augment the glutathione system in the cochlea may be protective against noise-induced hearing loss.

Acoustic Stimulation↗
PubMed2003

Noise exposure in the orthopaedic operating theatre: a significant health hazard.

BACKGROUND: Surgeons working in orthopedic operating theatres are exposed to significant noise pollution due to the use of powered instruments. This may carry a risk of noise-induced hearing loss. The present study was designed to quantify the noise exposure experienced by surgeons and establish whether this breaches occupational health guidelines for workplace noise exposure. METHODS: A sound dosimeter was worn by the operating surgeon during three total hip replacements and two total knee replacements. A timed record of the procedures was kept concurrently. Noise levels experienced during each part of the procedure and total noise exposures were measured. Noise exposures were compared with occupational health guidelines. RESULTS: Noise exposure in total hip replacement averaged 4.5% (1.52-6.45%) of the allowed daily dose (average duration 77.28 min). Total knee replacement exposure was 5.74% (4.09-7.39%) of allowed daily exposure (average duration: 69.76 min). Maximum sound levels approached but did not exceed recommended limits of 110 dBA (108.3 dBA in total hip replacement and 107.6 dBA in total knee replacement). Transient peak sound levels exceeded maximums of 140 dB on multiple occasions during surgery. CONCLUSIONS: Overall total noise dose during orthopaedic surgery was acceptable but orthopaedic surgeons experience brief periods of noise exposure in excess of legislated guidelines. This constitutes a noise hazard and carries a significant, but unquantified risk for noise-induced hearing loss.

Arthroplasty, Replacement↗
PubMed1998

Effects of background noise on click-evoked otoacoustic emissions.

OBJECTIVE: To investigate the effect of increased levels of background noise on click-evoked otoacoustic emission (CEOAE) recordings and to compare the effectiveness of the default CEOAE program with the QuickScreen CEOAE program in increased levels of noise, using an Otodynamics ILO88 recording device. DESIGN: The right ears of 40 young adult women with normal hearing were assessed using CEOAEs under four different noise conditions and with two different methods of data collection. The noise conditions were in quiet, 50 dB A, 55 dB A, and 60 dB A of white noise. Data were collected at each noise level in the default mode and also using the ILO88 QuickScreen program. RESULTS: There was a significant change in a number of important CEOAE output parameters with increased noise. In the default mode, mean whole wave reproducibility was 89.2% in quiet but declined to 85% with 50 dB A of white noise, 65% at 55 dB A and 20% at 60 dB A. The QuickScreen program proved more robust to the effects of noise than the default. In that mode, mean whole wave reproducibility was 91.7% in quiet, 92.5% with 50 dB A of white noise, 82.5% at 55 dB A and 45% at 60 dB A. CONCLUSIONS: The findings of the study indicate ambient noise levels for accurate CEOAE recording should not exceed 50 to 55 dB A of noise and alternatives to the default program should be considered in non-sound-treated situations.

Acoustic Stimulation↗
PubMed2004

Prior heat acclimation confers protection against noise-induced hearing loss.

Exposure to intense noise stress can cause a permanent noise-induced hearing loss which is thought to be due to elevation of reactive oxygen species in excess of the inherent antioxidant mechanisms of the cell. However, preconditioning to low levels of stress of one type can activate cellular mechanisms leading to the elevation of antioxidant levels so that the cell is then better able to tolerate subsequent severe stress of a different type. This has been called cross-tolerance. Here, we tested this hypothesis by acclimating rats to a moderate heat stress (30 days at 34 degrees C). The rats were exposed to 113 dB SPL noise for 3 days (12 h/day) in three different groups: heat acclimated then noise exposed; noise exposed and then heat acclimated; heat acclimated, then noise exposed and then heat acclimated again. Permanent changes in auditory function--auditory nerve brainstem evoked responses (ABR) and distortion product otoacoustic emissions (DPOAEs)--were evaluated in each of these animals and compared with those in rats exposed to noise only and in control groups of rats. Statistical evaluation of the results showed that when assessed with ABR, each of the heat-acclimated, noise-exposed groups was protected from the noise, even the group that was heat-acclimated after the noise exposure. When assessed with DPOAE, protection was statistically apparent only in the group that was heat acclimated, then exposed to noise, and not in the other groups. Thus, heat acclimation provides protection against permanent noise-induced hearing loss.

Acclimatization↗
PubMed2001

[Hearing impairment in the plastics industry workers exposed to styrene and noise].

Styrene exerts ototoxic effect in animals, and the combined exposure to this solvent and noise produces a synergistic effect relative to the isolated exposure to noise. However, there is a lack of reliable evidence that chronic occupational exposure to styrene is ototoxic to humans. Neither has been documented its additive effect with noise. The present study was aimed to assess hearing impairment and the risk of hearing loss in workers exposed to both styrene and noise. The study group included 72 male workers occupationally exposed to styrene in the plastics industry. The results were compared with two control groups, matched by age, gender and personal traits: one group composed of 82 male workers employed in a printing house and exposed only to noise at the levels almost twice as high as those observed in the group exposed to styrene and noise, and the other consisted of 65 male workers exposed neither to solvents nor to noise at workplace. In the group exposed to styrene and noise, significantly increased average hearing loss, as compared to both control groups, was found at all frequencies (1-8 kHz). The risk of hearing loss in the group exposed to styrene and noise was seven times higher (RR: 6.6; 3.0-15.9) than in the non-exposed group, and four times higher (RR: 4.0; 1.8-9.1) than in when workers exposed only to noise. However, no relationship could be observed between the amount of styrene exposure and hearing impairment, taking account of the confounding effect of noise and age. The results of the study suggest that the exposure to solvent mixtures with styrene as a basic component may exert additional, to noise, adverse effect on the auditory organ.

Acetone↗