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PubMed1996

Effects of noise and exercise on distortion product otoacoustic emissions.

The effect of physical exercise on both distortion product otoacoustic emissions (DPOAE), and on the temporary effects of noise on human cochlear function was examined. Changes in DPOAEs were compared to changes in behavioural thresholds and the possible relation between contralateral suppression of DPOAEs and susceptibility to noise exposure was investigated. Békésy audiometry, tympanometry and DPOAEs were measured in 8 subjects on 3 separate occasions: before and after noise exposure; before and after exercise at 60% of maximal oxygen uptake (VO2max); and before and after a combination of noise exposure and exercise, all of 10 min duration. Noise exposure was third-octave band noise of 102 dB SPL centered at 2 kHz. The magnitude of the effect of noise exposure on DPOAE amplitude averaged in the 2-4 kHz range was comparable but weakly correlated to the magnitude of the temporary threshold shift (TTS) measured as the change in Békésy threshold at 3 kHz. There was no effect of physical exercise without noise exposure on either the Békésy threshold or the DPOAE amplitude. Physical exercise significantly increased the noise-induced TTS and the effect of noise exposure on DPOAE amplitude. A positive correlation was found between the temporary effect of noise exposure and the contralateral suppression effect on DPOAE amplitude.

Acoustic Impedance Tests↗
PubMed2005

Involvement of nitric oxide generation in noise-induced temporary threshold shift in guinea pigs.

The present study explored the role of endogenous nitric oxide (NO) in the temporary threshold shift caused by acoustic trauma. Guinea pigs were exposed to broadband white noise at a level of 105+/-2dB sound pressure level (SPL) for 10min, causing a temporary threshold shift (TTS). The guinea pigs were divided into six groups (N-1 to N-6) according to survival days after noise exposure (0, 1, 2, 3, 7, 28days). Auditory brainstem responses (ABR) were recorded before noise exposure, immediately after noise exposure and before sacrifice. Immediately after animals were sacrificed, the stria vascularis and the spiral ligament of the lateral wall of each individual cochlea were harvest as a unit and prepared for assay of NO. There was a significant correlation (P<0.001) between the NO concentration and final ABR threshold in the noise exposure groups. But the return of ABR threshold to pre-noise-exposed level is early than that of NO concentration. An average 16.2dB threshold shift was found immediately after noise exposure. The threshold returned to the pre-noise-exposed level on the second post-exposure day. Comparing to unexposed control animals, the NO concentration increased nearly threefold immediately following noise exposure and decreased to twofold when the hearing threshold had returned to the pre-noise-exposed level. On the seventh post-exposure day the NO concentration was not different from that in unexposed control animals. Those findings indicate that endogenous NO is generated in the noise-induced temporal threshold shift and its concentration is correlated with the hearing loss.

Animals↗
PubMed2005

Loud speech in realistic environmental noise: phonetogram data, perceptual voice quality, subjective ratings, and gender differences in healthy speakers.

A new method for cancelling background noise from running speech was used to study voice production during realistic environmental noise exposure. Normal subjects, 12 women and 11 men, read a text in five conditions: quiet, soft continuous noise (75 dBA to 70 dBA), day-care babble (74 dBA), disco (87 dBA), and loud continuous noise (78 dBA to 85 dBA). The noise was presented over loudspeakers and then removed from the recordings in an off-line processing operation. The voice signals were analyzed acoustically with an automatic phonetograph and perceptually by four expert listeners. Subjective data were collected after each vocal loading task. The perceptual parameters press, instability, and roughness increased significantly as an effect of speaking loudly over noise, whereas vocal fry decreased. Having to make oneself heard over noise resulted in higher SPL and F0, as expected, and in higher phonation time. The total reading time was slightly longer in continuous noise than in intermittent noise. The women had 4 dB lower voice SPL overall and increased their phonation time more in noise than did the men. Subjectively, women reported less success making themselves heard and higher effort. The results support the contention that female voices are more vulnerable to vocal loading in background noise.

Acoustics↗
PubMed2006

Acoustic noise in functional magnetic resonance imaging reduces pain unpleasantness ratings.

Functional magnetic resonance imaging (fMRI) is increasingly used in cognitive studies. Unfortunately, the scanner produces acoustic noise during the image acquisition process. Interference from acoustic noise is known to affect auditory, visual and motor processing, raising the possibility that acoustic interference may also modulate processing of other sensory modalities such as pain. With the increasing use of fMRI in the investigation of the mechanisms of pain perception, particularly in relation to attention, this issue has become highly relevant. Pain is a complex experience, composed of sensory-discriminative, affective-motivational and cognitive-evaluative components. The aim of this experiment was to assess the effect of MRI scanner noise, compared to white noise, on the affective (unpleasantness) and the sensory-discriminative (localisation) components of pain. Painful radiant heat from a CO(2) laser was delivered to the skin of the right forearm in 24 healthy volunteers. The volunteers attended to either pain location or pain unpleasantness during three conditions: i) no noise, ii) exposure to MRI scanner noise (85 dB) or iii) exposure to white noise (85 dB). Both MRI scanner noise and white noise significantly reduced unpleasantness ratings (from 5.1 +/- 1.6 in the control condition to 4.7 +/- 1.5 (P = 0.002) and 4.6 +/- 1.6 (P < 0.001) with scanner and white noise respectively), whereas the ability to localise pain was not significantly affected (from 85.4 +/- 9.2% correct in the control condition to 83.1 +/- 10.3% (P = 0.06) and 83.9 +/- 9.5% (P = 0.27) with MRI scanner and white noise respectively). This phenomenon should be taken into account in the design of fMRI studies into human pain perception.

Acoustic Stimulation↗
PubMedDate not supplied

Aircraft and road traffic noise and children's cognition and health: a cross-national study.

BACKGROUND: Exposure to environmental stressors can impair children's health and their cognitive development. The effects of air pollution, lead, and chemicals have been studied, but there has been less emphasis on the effects of noise. Our aim, therefore, was to assess the effect of exposure to aircraft and road traffic noise on cognitive performance and health in children. METHODS: We did a cross-national, cross-sectional study in which we assessed 2844 of 3207 children aged 9-10 years who were attending 89 schools of 77 approached in the Netherlands, 27 in Spain, and 30 in the UK located in local authority areas around three major airports. We selected children by extent of exposure to external aircraft and road traffic noise at school as predicted from noise contour maps, modelling, and on-site measurements, and matched schools within countries for socioeconomic status. We measured cognitive and health outcomes with standardised tests and questionnaires administered in the classroom. We also used a questionnaire to obtain information from parents about socioeconomic status, their education, and ethnic origin. FINDINGS: We identified linear exposure-effect associations between exposure to chronic aircraft noise and impairment of reading comprehension (p=0.0097) and recognition memory (p=0.0141), and a non-linear association with annoyance (p<0.0001) maintained after adjustment for mother's education, socioeconomic status, longstanding illness, and extent of classroom insulation against noise. Exposure to road traffic noise was linearly associated with increases in episodic memory (conceptual recall: p=0.0066; information recall: p=0.0489), but also with annoyance (p=0.0047). Neither aircraft noise nor traffic noise affected sustained attention, self-reported health, or overall mental health. INTERPRETATION: Our findings indicate that a chronic environmental stressor-aircraft noise-could impair cognitive development in children, specifically reading comprehension. Schools exposed to high levels of aircraft noise are not healthy educational environments.

Aircraft↗
PubMed2001

The influence of external and internal noise on the detection of increments and decrements in the level of sinusoids.

This paper examines the influence of external and internal noise on the detection of increments and decrements in the level of sinusoidal pedestals. In experiment 1, the pedestals were presented either 18 dB above the masked threshold in broadband noise (condition 18-Masked) or 18 dB above the absolute threshold (condition 18-Abs). Pedestal frequencies were 250, 1000 or 4000 Hz, and increment/decrement durations ranged from 5 to 200 ms. For condition 18-Masked, thresholds decreased with increasing pedestal frequency, while for condition 18-Abs, thresholds did not change significantly with pedestal frequency. These results are consistent with the idea that, in condition 18-Masked, thresholds were influenced by the inherent fluctuations produced by the background noise at the output of the auditory filter centred at the pedestal frequency. These fluctuations would decrease in rate with decreasing centre frequency, and this might have a greater deleterious effect on performance. In contrast, the characteristics of the internal noise that presumably limited performance in condition 18-Abs do not appear to vary with pedestal frequency. In experiment 2, a 4000 Hz pedestal was used. It was presented either in quiet or in the presence of narrowband noise centred at 4000, or 7000 Hz, or both. The noise bandwidth ranged from 50 to 400 Hz. The increment/decrement duration ranged from 5 to 100 ms. The noise centred at 7000 Hz produced only a small deterioration in performance relative to that measured in quiet. The noise centred at 4000 Hz had a larger effect, and the effect increased with decreasing noise bandwidth. This is consistent with the idea that slow fluctuations at the output of the auditory filter impair increment and decrement detection more than rapid fluctuations. A model is proposed to account for the results, based on a simulated auditory filter, a compressive non-linearity, a sliding temporal integrator, a logarithmic transform and a template mechanism. Analysis using the model suggests that the effect of centre frequency observed in experiment 1, when background noise was present, cannot be explained entirely in terms of the fluctuations produced by the background noise at the output of the auditory filter centred at the pedestal frequency.

Acoustic Stimulation↗
PubMed2001

Potentiation of noise-induced hearing loss by amikacin in guinea pigs.

Noise and aminoglycosides initially attack cochlear outer hair cells (OHCs). Distortion product otoacoustic emissions (DPOAEs) are used for the early diagnosis of damage to OHCs. The effects of sub-damaging doses of amikacin, an aminoglycoside antibiotic agent, on noise-induced hearing loss (NIHL) were examined in guinea pigs. Animals were grouped by gender and exposed to broadband noise at 105 dB SPL for 12 h and/or injected i.m. with either amikacin (100 mg/kg/day) or saline for 10 days. Auditory brainstem response (ABR) thresholds, along with DPOAE amplitudes, were measured serially before and after noise exposure. DPOAE amplitudes decreased and ABR thresholds elevated immediately after noise exposure and then gradually recovered. At all frequencies, the emission amplitudes recovered completely to pre-exposure baseline values by 4 days after noise exposure. There was no effect of amikacin on either the ABR threshold or DPOAE amplitudes, in animals treated with amikacin only. However, amikacin significantly prolonged the effect of noise exposure on DPOAE amplitude but not on the noise-induced temporary threshold shift (TTS) of the ABR. In animals treated with a combination of noise and amikacin, significant changes in DPOAE amplitudes were still observed at 4 weeks after cessation of noise exposure. No gender difference in the responses to noise and/or amikacin could be demonstrated. The present findings indicate that even sub-damaging dosages of amikacin might impair recovery from NIHL in guinea pigs.

Amikacin↗
PubMedDate not supplied

State-dependent effects of Na channel noise on neuronal burst generation.

We explore the effects of stochastic sodium (Na) channel activation on the variability and dynamics of spiking and bursting in a model neuron. The complete model segregates Hodgin-Huxley-type currents into two compartments, and undergoes applied current-dependent bifurcations between regimes of periodic bursting, chaotic bursting, and tonic spiking. Noise is added to simulate variable, finite sizes of the population of Na channels in the fast spiking compartment. During tonic firing, Na channel noise causes variability in interspike intervals (ISIs). The variance, as well as the sensitivity to noise, depend on the model's biophysical complexity. They are smallest in an isolated spiking compartment; increase significantly upon coupling to a passive compartment; and increase again when the second compartment also includes slow-acting currents. In this full model, sufficient noise can convert tonic firing into bursting. During bursting, the actions of Na channel noise are state-dependent. The higher the noise level, the greater the jitter in spike timing within bursts. The noise makes the burst durations of periodic regimes variable, while decreasing burst length duration and variance in a chaotic regime. Na channel noise blurs the sharp transitions of spike time and burst length seen at the bifurcations of the noise-free model. Close to such a bifurcation, the burst behaviors of previously periodic and chaotic regimes become essentially indistinguishable. We discuss biophysical mechanisms, dynamical interpretations and physiological implications. We suggest that noise associated with finite populations of Na channels could evoke very different effects on the intrinsic variability of spiking and bursting discharges, depending on a biological neuron's complexity and applied current-dependent state. We find that simulated channel noise in the model neuron qualitatively replicates the observed variability in burst length and interburst interval in an isolated biological bursting neuron.

Action Potentials↗
PubMed2002

Spectral contributions to the benefit from spatial separation of speech and noise.

Speech recognition in noise improves when speech and noise sources are separated in space. This benefit has two components whose effects are strongest in different frequency regions: (1) interaural level differences (e.g., head shadow), which are largest at higher frequencies, and (2) interaural time differences, which have their greatest contribution at lower frequencies. Binaural interactions enhance the separation of signals from noise through the use of these interaural differences. Here, the benefit attributable to spatial separation was measured as a function of the low- and high-pass cutoff frequency of speech and noise. Listeners were younger adults with normal hearing, older adults with normal hearing, and older adults with hearing loss. Binaural thresholds for narrowband noises were measured in quiet and in a speech-shaped masker as a function of masker low-pass cutoff frequency. Speech levels corresponding to 50% correct recognition of sentences from the Hearing in Noise Test (HINT) were measured in a 65-dB SPL speech-shaped noise. Thresholds for narrowband noises and for speech were measured with two loudspeaker configurations: (1) signals and speech-shaped noise at 0 degrees azimuth (in front of the listener) and (2) signals at 0 degrees azimuth and speech-shaped noise at 90 degrees azimuth (at the listener's side). The criterion measure was spatial separation benefit, or the difference in thresholds for the two conditions. Benefit of spatial separation for unfiltered speech averaged 6.1 dB for younger listeners with normal hearing, 4.9 dB for older listeners with normal hearing, and 2.7 dB for older listeners with hearing loss. Benefit was differentially affected by low-pass and high-pass filtering, suggesting a trade-off of the contributions of higher frequency interaural level differences and lower frequency interaural timing cues. As expected, older listeners with hearing loss benefited little from the improved signal-to-noise ratios in the higher frequencies resulting from head shadow, but showed some benefit from lower frequency cues. Spatial benefit for older listeners with normal hearing was reduced relative to benefit for younger listeners. This result may be related to older listeners' elevated thresholds at frequencies above 6.0 kHz.

Adult↗
PubMed1995

Speech recognition in amplitude-modulated noise of listeners with normal and listeners with impaired hearing.

The effect of amplitude-modulated (AM) noise on speech recognition in listeners with normal and impaired hearing was investigated in two experiments. In the first experiment nonsense syllables were presented in high-pass steady-state or AM noise to determine whether the release from masking in AM noise relative to steady-state noise was significantly different between normal-hearing and hearing-impaired subjects when the two groups listened under equivalent masker conditions. The normal-hearing subjects were tested in the experimental noise under two conditions: (a) in a spectrally shaped broadband noise that produced pure tone thresholds equivalent to those of the hearing-impaired subjects, and (b) without the spectrally shaped broadband noise. The release from masking in AM noise was significantly greater for the normal-hearing group than for either the hearing-impaired or masked normal-hearing groups. In the second experiment, normal-hearing and hearing-impaired subjects identified nonsense syllables in isolation and target words in sentences in steady-state or AM noise adjusted to approximate the spectral shape and gain of a hearing aid prescription. The release from masking was significantly less for the subjects with impaired hearing. These data suggest that hearing-impaired listeners obtain less release from masking in AM noise than do normal-hearing listeners even when both the speech and noise are presented at levels that are above threshold over much of the speech frequency range.

Adult↗
PubMed2001

The human temporary threshold shift after exposure to 60 minutes' noise in an aerobics class.

The potential hazard of noise to hearing is well documented. However, there are some experiences of noise-induced hearing loss (NIHL) that are not so well-known, for example the effects of leisure noise, and in particular, leisure noise experienced during an aerobics class. A preliminary study of the noise level in aerobics classes in the Manchester region was carried out and their mean noise level was found to be 89.6 dB(A) (+/-4.7 dB(A)). Pure tone thresholds in the audible frequency range were obtained from 28 young adult volunteers (mean age 21 years; standard deviation (SD) 2.3 years) and 14 subjects (the 'exposure' group) were then invited to join (but not participate in) an aerobics class (mean noise level 91.8 dB(A) (+/-1.5 dB(A)) for 60 minutes. The noise levels in the aerobics class were monitored throughout the 60 minutes and the subjects did not stray from a small marked area (2 m2). Subjects' hearing thresholds were obtained for a second time, beginning within 2 minutes of the cessation of the noise, and any temporary threshold shifts (TTS) were noted. A second group of 14 subjects (the control group) was invited for a second audiogram after at least 60 minutes, during which time subjects were not exposed to any noise. The data obtained here were analysed and of the 14 subjects in the exposure group all had significant TTS at all frequencies except 1,000 Hz. Subjects in the control group, who had not experienced any noise, showed significantly reduced hearing thresholds (all frequencies; p>0.02), showing evidence of a possible practice effect with audiometric testing.

Audiometry, Pure-Tone↗
PubMed2004

Noise exposure and hearing loss among sand and gravel miners.

The objectives of this study were to describe workplace noise exposures, risk factors for hearing loss, and hearing levels among sand and gravel miners, and to determine whether full shift noise exposures resulted in changes in hearing thresholds from baseline values. Sand and gravel miners (n = 317) were interviewed regarding medical history, leisure-time and occupational noise exposure, other occupational exposures, and use of hearing protection. Audiometric tests were performed both before the work shift (following a 12-hour noise-free interval) and immediately following the work shift. Full shift noise dosimetry was conducted. Miners' noise exposures exceeded the Recommended Exposure Limit (REL) of the National Institute for Occupational Safety and Health (NIOSH) for 69% of workers, and exceeded the Mine Safety and Health Administration's action level for enrollment in a hearing conservation program for 41% of workers. Significantly higher noise exposures occurred among employees of small companies, among workers with a job classification of truck driver, among males, and among black workers. Hearing protection usage was low, with 48% of subjects reporting that they never used hearing protection. Hearing impairment, as defined by NIOSH, was present among 37% of 275 subjects with valid audiograms. Black male workers and white male workers had higher hearing thresholds than males from a comparison North Carolina population unexposed to industrial noise. Small but statistically significant changes in hearing thresholds occurred following full shift noise exposure among subjects who had good hearing sensitivity at baseline. In a logistic regression model, age and history of a past noisy job were significant predictors of hearing impairment. Overall, sand and gravel workers have excessive noise exposures and significant hearing loss, and demonstrate inadequate use of hearing protection. Well-designed hearing conservation programs, with reduction of noise exposure, are clearly needed.

Adolescent↗
PubMedDate not supplied

Personal interaction with a Reiki practitioner decreases noise-induced microvascular damage in an animal model.

OBJECTIVE: To determine whether Reiki, a process of transmission of healing energy, can significantly reduce microvascular leakage caused by exposure to excessive noise using an animal model. RATIONALE: Reiki is beginning to be used in hospitals to accelerate recovery. Despite many anecdotes describing Reiki's success, few scientific studies are reported and none of those use animals. Animal models have the advantage over human subjects in that they provide well-controlled, easily interpretable experiments. The use of noise is relevant to hospital patients because of the excessive ambient noise in hospitals in the United Kingdom and United States. Loud noise can lead to several nonauditory disorders in humans and animals that impair recovery. In the rat, stress from noise damages the mesenteric microvasculature, leading to leakage of plasma into the surrounding tissue. DESIGN: One group of four rats simultaneously received daily noise and Reiki, while two other groups received "sham" Reiki or noise alone. A fourth group did not receive noise or additional treatment. The experiment was performed three times to test for reproducibility. OUTCOME MEASURES: Average number and area of microvascular leaks to fluorescent albumin per unit length of venule. RESULTS: In all three experiments, Reiki significantly reduced the outcome measures compared to the other noise groups (sham Reiki and noise alone) (p < 0.01). CONCLUSIONS: Application of Reiki significantly reduces noise-induced microvascular leakage in an animal model. Whether or not these effects are caused by Reiki itself, or the relaxing effect of the Reiki practitioner, this procedure could be useful for minimizing effects of environmental stress on research animals and hospital patients.

Animals↗
PubMed1991

Attenuation of low-frequency noise by hearing protectors.

The ability of earmuffs and helmets to reduce low-frequency (4-250 Hz) noise was tested in an anechoic chamber, in a paint factory, outside and in a low-frequency noise chamber. Prototypes of a new noise helmet were also tested. Steady noise and low-frequency noise impulses were used as the sound sources. The testing was sometimes difficult because physiological noise raised the sound level inside the hearing protector at some frequencies after the protector was put on. Therefore the low-frequency sound level had to be over 100 dB at frequencies of 2-250 Hz during the tests. The earmuffs attenuated noise levels of 1-20 dB in the 4-250 Hz frequency range. Commercial noise helmets tested were not as good as earmuffs in attenuating low-frequency noise. New noise helmet prototypes attenuated low-frequency noise better than did earmuffs or commercial helmets (attenuation 5-39 dB).

Ear Protective Devices↗
PubMed1993

Detection of warble tones in wideband noise with and without hearing protection devices.

Noise attenuation by linear hearing protection devices (HPDs) is considered to be independent of the environmental noise level. Linearity of HPDs is one of the basic assumptions underlying the Real Ear Attenuation at the Threshold (REAT) method of HPD testing, which utilizes quiet conditions. However, non-linear growth of masking at high intensity levels may result in the effects of HPDs on detection of speech and warning signals being different from those at high noise levels. The purpose of this study was to determine if the non-linear growth of masking can affect detection of warble signals by persons using HPDs in wideband noise presented at the 100 dB(A) level. Audiometric thresholds of hearing of 10 listeners were measured under four experimental conditions: (1) noise off, HPDs off (condition C1); (2) noise off, HPDs on (condition C2); (3) noise on, HPDs on (condition C3); and (4) noise on, HPDs off (condition C4). The results of this study indicate that detection of signals by persons using HPDs in noise < 100 dB(A) can be well predicted from noise attenuation characteristics of HPDs measured in quiet without the need for a correction factor accommodating non-linear growth of masking. This finding has implications for predicting the audibility of warning signals in noise by persons wearing HPDs.

Adult↗
PubMed2002

Noise in the postanaesthesia care unit.

BACKGROUND: Although the postanaesthesia care unit (PACU) can be noisy, the effect of noise on patients recovering from anaesthesia is unknown. We studied the sources and intensity of noise in the PACU and assessed its effect on patients' comfort. METHODS: We measured noise in a five-bed PACU with a sound level meter. Noise levels were obtained using an A-weighted setting (dBA) and peak sound using a linear scale (dBL). Leq (average noise level at 5-s intervals), maximum Leq (LeqMax), minimum Leq (LeqMin) and noise peaks (Lpc) were calculated. During recording, an independent observer noted the origin of sounds from alarms and noise above 65 dB intensity (P65dB). Two hours after leaving the PACU, patients were asked about their experience and to rank their complaints on a visual analogue scale (VAS) using unstructured and structured questionnaires. RESULTS: We made 20,187 measurements over 1678 min. The mean Leq, LeqMax and LeqMin were 67.1 (SD 5.0), 75.7 (4.8) and 48.6 (4.1) dBA respectively. The mean Lpc was 126.2 (4.3) dBL. Five per cent of the noise was at a level above 65 dBA. Staff conversation caused 56% of sounds greater than 65 dB and other noise sources (alarm, telephone, nursing care) were each less than 10% of these sounds. Five patients reported disturbance from noise. There was no significant difference in Leq measured for patients who found the PACU noisy and those who did not [59.5 (3.1) and 59.4 (2.4) dBA respectively]. Stepwise multiple logistic regression indicated that only pain was associated with discomfort. CONCLUSIONS: Even though sound in the PACU exceeded the internationally recommended intensity (40 dBA), it did not cause discomfort. Conversation was the most common cause of excess noise.

Adult↗
PubMed1991

Relative and combined effects of heat and noise exposure on sleep in humans.

In a counter-balanced design, the effects of daytime and/or nighttime exposure to heat and/or traffic noise on night sleep were studied in eight healthy young men. During the day, the subjects were exposed to baseline condition (ambient temperature = 20 degrees C; no noise) or to both heat (35 degrees C) and noise. The duration of the daytime exposure was 8 h ending 5 h before sleep onset. The following nights, the subjects slept either in undisturbed (20 degrees C; no noise) or in noise, heat, or noise plus heat-disturbed environments. During the day, the various types of traffic noise were distributed at a rate of 48/h with peak intensities ranging between 79 and 86 dB(A). The background noise level was at 45 dB(A). At night, the peak intensities were reduced by 15 dB(A), the rate was diminished to 9/h, and the background noise was at 30 dB(A). Electrophysiological measures of sleep and esophageal and mean skin temperatures were continuously recorded. The results showed that both objective and subjective measures of sleep were more disturbed by heat than by noise. The thermal load had a larger impact on sleep quality than on sleep architecture. In the nocturnal hot condition, total sleep time decreased while duration of wakefulness, number of sleep stage changes, stage 1 episodes, number of awakenings, and transitions toward waking increased. An increase in the frequency of transient activation phases was also found in slow-wave sleep and in stage 2. In the nocturnal noise condition, only total number of sleep stage changes, changes to waking, and number of stage 1 episodes increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Ototoxic effects of occupational exposure to styrene and co-exposure to styrene and noise.

Ototoxicity of styrene and the synergistic action of styrene and noise have been shown in rats. The respective data in humans are scarce and equivocal. This study evaluated the effects of occupational exposure to styrene and combined exposures to styrene and noise on hearing. The study group, comprised of 290-yacht yard and plastic factory workers, was exposed to a mixture of organic solvents, having styrene as its main compound. The reference group, totaling 223 subjects, included (1) white-collar workers, exposed neither to solvents nor noise and (2) metal factory workers, exposed exclusively to noise. All subjects were assessed by means of a detailed questionnaire and underwent otorhinolaryngological and audiometric examinations. Multiple logistic regression analysis revealed almost a 4-fold (or 3.9; 95% CI = 2.4-6.2) increase in the odds of developing hearing loss related to styrene exposure. The factors adjusted for were: age, gender, current occupational exposure to noise, and exposure to noise in the past. In cases of the combined exposures to styrene and noise, the odds ratios were two to three times higher than the respective values for styrene-only and noise-only exposed subjects. The mean hearing thresholds--adjusted for age, gender, and exposure to noise--were significantly higher in the solvent-exposed group than in the unexposed reference group at all frequencies tested. A positive linear relationship existed between an averaged working life exposure to styrene concentration and a hearing threshold at the frequencies of 6 and 8 kHz. This study provides the epidemiological evidence that occupational exposure to styrene is related to an increased risk of hearing loss. Combined exposures to noise and styrene seem to be more ototoxic than exposure to noise alone.

Adult↗