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PubMed1991

[Clinical study of speech understanding in noise].

The goal of this study was to determine the extent to which the difficulty frequently experienced by hearing-impaired listeners in understanding noisy speech can be clinically described in terms of the auditory site of lesion. To this end, shifts of speech reception threshold in noise, using standardized franco-québécois bisyllabic word lists, were obtained from noise-exposed workers and compared to Plomp's model to ascertain content validity. Shifts resulted from monaural listening to a broad-band speech spectrum noise held constant at 0 dB signal-to-noise ratio. In this manner, increasing the presentation levels of both speech and noise was expected to progressively minimize the contribution of Plomp's class A attenuation component to speech hearing loss and eventually show an unequivocal manifestation of its distortion component (class D speech hearing loss). Listeners were 457 noise-exposed workers giving a total of 914 observations. Rejection of those ears with suspected middle-ear pathology led to a reduction to a total of 709 observations representing various degrees of permanent hearing impairment. An additional 98 observations showed normal hearing sensitivity in spite of noise exposure averaging 9.6 years. Results indicated the presence of five categories of speech threshold shifts varying independently of hearing sensitivity. 59.8% of those observations with permanent hearing impairment (424/709) simultaneously showed a problem understanding speech in noise. On 78 occasions, listening in noise was so disturbed that the 50% performance level corresponding to the speech threshold could no longer be established within reasonable limits, that is up to 65 dB above the speech threshold in a quiet environment. Conversely, 26.5% of the observations with essentially normal hearing sensitivity (26/98) showed reduced speech reception in noise. Fitting Plomp's model confirmed our expectations for two of the five categories of scores. A principal component analysis identified similar behaviour of speech threshold shifts in noise compared with Plomp's class D speech hearing loss. Hence, these speech threshold shifts in noise were interpreted as predominantly reflecting peripheral auditory disorders, that is defective frequency selectivity and temporal resolution. The remaining categories were found to be under the predominant influence of two other mechanisms: (1) band width reduction resulting from impaired hearing; (2) disorders associated with certain non-auditory cognitive factors, namely selective attention and the ability to make use of the redundancy of the message.

Adult↗
PubMedDate not supplied

[Annoyance, disturbance and damage caused by noise and vibrations].

The pathogenic effects derived by the emission of noises and vibrations, essentially, are conditioned from three etiological factors. The first of those is the energetic level of the sound emission, whereas the second is the exposure time and the last is the spectral composition. We, making reference to sound source, can associate to the first etiological factors the influence of impulsive components present in the noise; whereas to the second the importance of the functional recovery time of auditory acuity and, at last, to the third etiological factors the annoyance caused by the superimposition of pure tone or of tight band noise, contained in 1/3 of octave. The specific effects, caused by the noise exposure, affect the auditory system (acoustic trauma, auditory weariness, noise deafness) and the vestibular system (vertigo, sickness, trouble of balance). Those effects are fortly dependent to the entity of the sound energy accepted in a calculated time interval (LEP), and after the end of noise expositions they aren't developed. The specific effects became permanent when the degeneration of the Corti's cells occurred. The noise deafness, in first time, impair the frequencies included between 3000 and 6000 Hz, particularly it concerns the thigh band of 4000 Hz. Those lesions happen after a prolonged exposition to LEP greater than 80-85 dBA, and its evolutions, usually, follow a succession of clinical stages that can be monitored through audiometric controls to allow the necessary preventive measures. The nonspecific effects, derived to the noise exposition can be divided in: 1) neuroendocrinologic and psychological effects; 2) psychosomatic effects; 3) psychosocial effects. The psychological effects (anxiety, depression, conflict condiction) are strictly related with neuroendocrinological responses to the sound impact, this, for the smaller entity of stimulation, is identical to locality reaction, on the contrary for more violent stimulations those determine and adaptative reaction (Selye syndrome) that consist in a excitement of the thalamus and pituitary gland, this determines a multiple endocrine hyperactivity followed from a inhibition period or, possibly, an adaptation period. The noise exposure determines, besides, same E.E.G. alterations and a reduction of walls' tone of the brain's arteries. The psychosomatic effects of the noise appear with emission greater than or equal to 70 dBA and these can be distinguished in: cardiovascular effects, gastrointestinal effects, respiratory effects, visual and genitals effects. The noise in these cases, mainly, acts as a risk's factors. The noise is, again, the cause of the arising of psychosocial effects. These can be classified as: interference on the transmission and understanding of the words, perfect healthy respect the efficiency and the learning capacity of the exposed subject, interference on the duration and quality of the sleep.(ABSTRACT TRUNCATED AT 400 WORDS)

Hearing Loss, Noise-Induced↗
PubMed1979

Noise dosimeter measurements in the Air Force.

Personal noise dosimeter monitoring devices, operating on the Air Force rule of 4 dB per doubling time and 84 dB(A) criterion level, have been used for the past year in determining the occupational noise exposures of Air Force personnel working in hazardously noisy jobs. The research conducted by the Aerospace Medical Research Laboratory has resulted to date in 418 8-h occupational noise exposure measurements being collected on 120 different individuals. The 8-h occupational noise levels ranged from 66-111 dB(A) with the median level at 84.5 dB(A). In addition, noise dosimeters have been used at Air Force bases across the country in an experimental effort to see how well their use would fit in with existing Air Force hearing conservation programs. A total of 567 noise data measurements have been received from various bases. The base response data noise exposures ranged from 60-101 dB(A) with a median level of 80.1 dB(A). Along with the 8-h occupational noise exposure study, 16 individuals wore an equal energy noise dosimeter for 24-h or more to determine their nonoccupational noise exposure. A total of 73 separate 24-h measurements were taken. The median daily A-weighted average sound level was 77 dB(A). This is only 2 dB higher than the median of 75 dB(A) found for the typical American by previous studies. Some of the merits of noise dosimeters, as well as some of the problems involved in setting up ongoing noise monitoring programs, are discussed.

Adolescent↗
PubMed1986

Bioresponses in men after repeated exposures to single and simultaneous sinusoidal or stochastic whole body vibrations of varying bandwidths and noise.

This study deals with the changes in temporary hearing threshold (TTS2), upright body posture sway amplitudes in the X and Y direction, heart rate (HR), R-wave amplitude (RWA), systolic (SBP) and diastolic (DBP) blood pressure, pulse pressure (PP) and the index characterizing haemodynamic activity (HDI), when the subjects were exposed to noise alone, to vibrations alone or to simultaneous noise and vibrations. The experiments were carried out in an exposure chamber and the number of exposure combinations was 12. Seven healthy, male students volunteered as subjects, making a total number of 84 experiments. For each person the experiment consisted of a 30-min control period, five consecutive 16-min exposures, between which there was a 4-min measuring interval, and a 15-min recovery period. The noise was broadband (bandwidth 0.2-16.0 kHz) A-weighted (white) noise. The noise categories were: (1) no noise and (2) noise with an intensity of 90 dBA. The categories of low-frequency whole body vibration in the direction of the Z-axis were: (1) vibration within the range 4.4-5.6 Hz, (2) vibration within the range 2.8-5.6 Hz, (3) vibration within the range 2.8-11.2 Hz, (4) vibration within the range 1.4-11.2 Hz and (5) sinusoidal vibration with a frequency of 5 Hz. The (rms) acceleration in all the vibration models was 2.12 m/s2. The results showed that the TTS2 values at 4 and 6 kHz increased as a result of simultaneous exposure to noise and vibration significantly more than as a result of exposure to noise alone. The TTS2 values increased more intensely during the first 16-min exposure. The means of the variances in the amplitudes of body upright posture sway changed not only after exposures to vibration alone, but also after exposure to noise alone. The means of the sway variances in the X and Y directions at 0.1 Hz and within the range 0.06 to 2.00 Hz increased only when the vibration in the noise-vibration combination was sinusoidal. The changes in the heart rate, R-wave amplitude and blood pressure values also depended on the bandwidth of the vibration, the number of consecutive exposures and on whether the subjects were simultaneously exposed to noise in addition to vibration. As a rule, the effects of sinusoidal vibration differed from those due to stochastic vibrations.

Adult↗
PubMed2004

Noise exposure during noninvasive ventilation with a helmet, a nasal mask, and a facial mask.

OBJECTIVE: To assess noise exposure during noninvasive ventilation (NIV) with different types of interface (helmet, nasal, and facial masks). SUBJECTS AND METHODS: Ten "naive" healthy volunteers underwent NIV at pressure support levels of 10 and 15 cmH2O with: (a) helmet, (b) helmet equipped with HME filters at the junctions between the helmet and the inspiratory and expiratory branches of the respiratory circuit, (c) nasal mask, and (d) facial mask. Noise intensity was assessed with a sound level meter by placing a microphone near the right ear. Noise intensity and degree of discomfort were also assessed subjectively with a visual analogue scale. RESULTS: Inside the helmet noise exceeded 100 dB. Noise intensity was poorly affected by pressure support level and unaffected by the presence of HME filters. During NIV with nasal or facial masks the noise did not exceed 70 dB (i.e., noise was not louder than the usual noise background in ICU). Subjective evaluation of noise intensity mirrored objective measurements; however, the presence of HME filters was associated with the feeling of less noise inside the helmet. The discomfort associated with the helmet did not significantly differ from that associated with the masks. CONCLUSIONS: NIV helmet is associated with significantly greater noise than nasal and facial masks, but is as comfortable as masks, at least in the short term. Medium- and long-term exposure to loud noise may potentially impair ear function and increase the patient's discomfort.

Adult↗
PubMed1985

Temporal response features of cat auditory cortex neurons contributing to sensitivity to tones delivered in the presence of continuous noise.

Single cat auditory cortex neurons have limited intensity dynamic ranges for characteristic frequency (CF) tones. In the presence of continuous wide-spectrum noise, these cells' tone responses undergo a dynamic range shift towards higher SPLs. In the present study, the mechanisms underlying this dynamic range shift were examined by probing the sensitivity of the cells to CF tones delivered at various delays after the onset and/or offset of a long duration noise mask. Fifty cells were studied in the cortex of 7 anesthetized cats using acoustically mixed tonal and noise stimuli presented monaurally to the contralateral ear through a calibrated, sealed stimulating system. For most neurons, the dynamic range shift induced by continuous noise was fully developed in the responses to CF tones delivered 100-250 ms after the onset of a noise mask. For nonmonotonic cells, shorter delays between noise and tone onsets resulted in a profound suppression of tone responses that was consistent with the view that noise stimuli evoke a short latency, but transient, inhibitory response in these neurons. Studies of monotonic cells with short tone delays revealed that the usual excitatory response to noise onset was sometimes followed by a period of inhibition. In most cells, as soon after mask onset that CF tones were able to evoke spike discharges, those responses had latent periods comparable to those of responses to tones of the same SPL delivered in continuous noise. After the offset of an 800 ms noise mask effecting a 15-25 dB dynamic range shift for CF tones, recovery of tone sensitivity to within 5 dB of control levels typically took 50-200 ms. On the basis of these observations, it is argued that in order for a CF tone to excite a cortical neuron after the onset of a noise mask, the tone amplitude must be sufficient to overcome both the transient central neural consequences of noise onset, and a short-term adaptation that is probably peripheral in origin. The implications of these data for the sensitivity of cortical cells to temporally varying stimuli are discussed.

Animals↗
PubMed2005

Speech recognition abilities in noise for children with severe-to-profound unilateral hearing impairment.

OBJECTIVE: The purpose of this research was to compare the signal-to-noise ratio required for equal performance for children (aged 6-14 years) with normal hearing (N=17) versus those with severe-to-profound unilateral hearing impairment (N=20) who can be at a disadvantage, particularly when sounds are presented to the impaired ear. The listening environment is designed to approximate that which is encountered in a typical classroom. METHODS: All signals (Hearing in Noise Test-Children and Nonsense Syllable Test) were presented in the sound field from various azimuths with continuous noise presented from all quadrants. The children were required to repeat twenty items, from each test, in each listening condition. The intensity of the presentations was varied based on the accuracy of previous items. Average signal-to-noise ratios are compared between and within groups. RESULTS: (1) In most listening conditions, significantly greater signal-to-noise ratios were needed by those with unilateral hearing impairment than those with normal hearing, on both speech tests. (2) In every listening condition, both groups required significantly greater signal-to-noise ratios to perform equally well on the Nonsense Syllable Test as on the Hearing-In-Noise Test-Children. (3) For the Hearing-In-Noise Test-Children, children with normal hearing required significantly greater signal-to-noise ratios when facing the signal than when the signal was presented to a normally hearing ear (monaural direct). (4) On both tests, the children with unilateral hearing impairment required significantly greater signal-to-noise ratios when facing the signal than in the monaural direct condition. (5) On both tests, the children with unilateral hearing impairment required significantly greater signal-to-noise ratios when the signal was presented to the impaired ear (monaural indirect) than when facing the signal. CONCLUSIONS: (1) The children with unilateral hearing impairment require a more advantageous listening condition to perform equally as well as their normally hearing counterparts. (2) All of the children benefited from signals delivered in a monaural direct condition. (3) The children with unilateral hearing impairment performed best in the monaural direct condition or when facing the signal at zero degrees. (4) Significantly greater signal-to-noise ratios were needed for both groups when restricted contextual cues were available versus when sentential cues were available.

Adolescent↗
PubMed2000

Effect of noise exposure on rat cardiac peripheral benzodiazepine receptors.

Noise is an environmental physical agent, which is regarded as a stressful stimulus: impairment and modifications in biological functions are reported, after loud noise exposure, at several levels in human and animal organs and apparatuses, as well as in the endocrine, cardiovascular and nervous system. In the present study equilibrium binding parameters of peripheral benzodiazepine receptors (PBRs) labelled by the specific radioligand [3H]PK 11195, were evaluated in cardiac tissue of rats submitted to 6 or 12 h noise exposure and of rats treated "in vivo" with PBR ligands such as PK 11195, Ro54864, diazepam and then noise-exposed. Results revealed a statistically significant decrease in the maximum number of binding sites (Bmax) of [3H]PK 11195 in atrial membranes of 6 or 12 h noise exposed rats, compared with sham-exposed animals, without any change in the dissociation constant (Kd). The "in vivo" PBR ligand pre-treatment counteracted the noise-induced modifications of PBR density. As PBRs are mainly located on mitochondria we also investigated whether noise exposure can affect the [3H]PK 11195 binding parameters in isolated cardiac mitochondrial fractions. Results indicated a significant Bmax value decrease in right atrial mitochondrial fractions of rats 6 or 12 h noise-exposed. Furthermore, as PBR has been suggested to be a supramolecular complex that might coincide with the not-yet-established structure of the mitochondrial permeability transition (MPT)-pore, the status of the MPT-pore in isolated heart mitochondria was investigated in noise- and sham-exposed rats. The loss of absorbance associated with the calcium-induced MPT-pore opening was greater in mitochondria isolated from hearts of 6 h noise- than those of sham-exposed rats. In conclusion, these findings represent a further instance for PBR density decrease in response to a stressful stimulus, like noise; in addition they revealed that "in vivo" administration of PBR ligands significantly prevents this decrease. Finally, our data also suggest the involvement of MPT in the response of an organism to noise stress.

Animals↗
PubMed1996

Hazards of noise exposure on fetal hearing.

Many women of childbearing age are occupationally or recreationally exposed to hazardous levels of noise. Questions regarding the possibility of noise-induced hearing loss during fetal life have been posed. Advice to pregnant women regarding the safe limits of noise exposure has been lacking, because the evidence concerning the existence of fetal noise-induced hearing loss is sparse and the effects of intense noise exposures on the fetuses of pregnant women are largely unknown. Because of the nature of the fetal sound environment and the development of the ear, it is possible that fetal noise-induced hearing loss presents itself very differently than adult noise-induced hearing loss. Previous research in small mammals has suggested a critical period in development when susceptibility to noise exposure may be greater. Several investigations, using sheep as a model for in utero hearing loss, have provided evidence of fetal hearing changes after noise exposure. Although the reported epidemiological studies concerned with the possibility of fetal hearing loss had limitations, there were some suggestions of noise-induced hearing loss in children whose mothers experienced noise exposure. This article provides some background information concerning the possibility of fetal noise-induced hearing less.

Animals↗
PubMed2001

Chronic aircraft noise exposure, stress responses, mental health and cognitive performance in school children.

BACKGROUND: Previous research suggests that children are a high risk group vulnerable to the effects of chronic noise exposure. However, questions remain about the nature of the noise effects and the underlying causal mechanisms. This study addresses the effects of aircraft noise exposure on children around London Heathrow airport, in terms of stress responses, mental health and cognitive performance. The research also focuses on the underlying causal mechanisms contributing to the cognitive effects and potential confounding factors. METHODS: The cognitive performance and health of 340 children aged 8-11 years attending four schools in high aircraft noise areas (16 h outdoor Leq > 66 dBA) was compared with children attending four matched control schools exposed to lower levels of aircraft noise (16 h outdoor Leq < 57 dBA). Mental health and cognitive tests were group administered to the children in the schools. Salivary cortisol was measured in a subsample of children. RESULTS: Chronic aircraft noise exposure was associated with higher levels of noise annoyance and poorer reading comprehension measured by standardized scales with adjustments for age, deprivation and main language spoken. Chronic aircraft noise was not associated with mental health problems and raised cortisol secretion. The association between aircraft noise exposure and reading comprehension could not be accounted for by the mediating role of annoyance, confounding by social class, deprivation, main language or acute noise exposure. CONCLUSIONS: These results suggest that chronic aircraft noise exposure is associated with impaired reading comprehension and high levels of noise annoyance but not mental health problems in children.

Aircraft↗
PubMed2001

The West London Schools Study: the effects of chronic aircraft noise exposure on child health.

BACKGROUND: Previous field studies have indicated that children's cognitive performance is impaired by chronic aircraft noise exposure. However, these studies have not been of sufficient size to account adequately for the role of confounding factors. The objective of this study was to test whether cognitive impairments and stress responses (catecholamines, cortisol and perceived stress) are attributable to aircraft noise exposure after adjustment for school and individual level confounding factors and to examine whether children exposed to high levels of social disadvantage are at greater risk of noise effects. METHODS: The cognitive performance and health of 451 children aged 8-11 years, attending 10 schools in high aircraft noise areas (16 h outdoor Leq > 63 dBA) was compared with children attending 10 matched control schools exposed to lower levels of aircraft noise (16 h outdoor Leq < 57 dBA). RESULTS: Noise exposure was associated with impaired reading on difficult items and raised annoyance, after adjustment for age, main language spoken and household deprivation. There was no variation in the size of the noise effects in vulnerable subgroups of children. High levels of noise exposure were not associated with impairments in mean reading score, memory and attention or stress responses. Aircraft noise was weakly associated with hyperactivity and psychological morbidity. CONCLUSIONS: Chronic noise exposure is associated with raised noise annoyance in children. The cognitive results indicate that chronic aircraft noise exposure does not always lead to generalized cognitive effects but, rather, more selective cognitive impairments on difficult cognitive tests in children.

Aviation↗
PubMed2005

Sentence intelligibility in noise for listeners with normal hearing and hearing impairment: influence of measurement procedure and masking parameters.

Speech intelligibility measurements strongly depend on several procedural parameters. In order to obtain comparable results from different test procedures, these parameters must be investigated as to which should be standardized and which could be set freely. This study investigates the influence of noise level, noise type, and presentation mode on speech reception thresholds (SRTs), and intelligibility function slopes in noise for normal-hearing and hearing-impaired subjects. The noise presentation level had no significant influence on either SRTs or slope values, provided that the presentation level exceeded hearing threshold. Two stationary, speech-shaped noises produced identical results. Speech-simulating fluctuating noise yielded about 14 dB lower SRTs for normal-hearing subjects and about 10 dB lower SRTs for 20% of the heating-impaired subjects. Of the hearing-impaired subjects, 30% did not benefit from the modulations and showed similar SRTs as for stationary noise. Using continuous noise yielded lower SRTs compared to gated noise. However, the difference between the results in continuous and gated noise was not significant for the hearing-impaired subjects. A presentation level of 65 dB SPL (normal-hearing subjects) or 80 dB SPL (hearing-impaired subjects) and an interfering noise with a spectrum similar to the mean long-term average speech spectrum (LTASS) is suggested for comparable adaptive measurement procedures. A fluctuating, speech-shaped noise is recommended to differentiate between subjects.

Adult↗
PubMed2000

Effects of guidelines implementation in a surgical intensive care unit to control nighttime light and noise levels.

OBJECTIVE: Because of around-the-clock activities, environmental noise and light are among the many causes of sleep disturbance in an intensive care unit (ICU). The implementation of guidelines may potentially change behavior rules and improve sleep quality. DESIGN: A prospective interventional study, observing the effects of simple nighttime guidelines on light and noise levels in an ICU. SETTING: A modern surgical ICU, subdivided into six identical three-bed rooms. PATIENTS: Critically ill adult patients. INTERVENTION: Between two observation periods, five guidelines were implemented to decrease both light and noise during the night shift in the patient's room. MEASUREMENT: Light levels and noise levels were obtained using a luxmeter and a sound level meter [A-weighted decibels (dB) scale] and were monitored continuously from 11 pm to 5 am both before (period P1) and after (period P2) the implementation of guidelines. MAIN RESULTS: Similar patient's gravity and nursing workload scores were observed between P1 and P2. A low mean (<5 Lux) and maximal light level were measured during both P1 and P2. The implementation of guidelines lowered mean light disturbance intensity with a greater variability of light during P2. All noise levels were high and corresponded more to a quiet office for noise level equivalents and to a busy restaurant for peak noise levels during both P1 and P2. Guidelines decreased the noise level equivalent (P1, 51.3 dB; P2, 48.3 dB), peak noise level (P1, 74.9 dB; P2, 70.8 dB), and the number of acoustic identified alarms (P1, 22.1 dB; P2, 15.8 dB) during P2. CONCLUSION: The night light levels were low during both periods, and lowering the light levels induced a greater variation of light, which may impair sleep quality. All measured noise levels were high during both periods, which could contribute to sleep disturbance, and the implementation of guidelines significantly lowers some important noise levels. The background noise level was unchanged.

Adult↗
PubMed2005

Effects of low-pass noise masking on auditory event-related potentials to speech.

OBJECTIVE: This study investigated the effects of decreased audibility in low-frequency spectral regions, produced by low-pass noise masking, on cortical event-related potentials (ERPs) to the speech sounds /ba/ and /da/. DESIGN: The speech sounds were presented to normal-hearing adults (N = 10) at 65- and 80-dB peak-to-peak equivalent SPL while they were engaged in an active condition (pressing a button to deviant sounds) and a passive condition (ignoring the stimuli and reading a book). Broadband masking noise was simultaneously presented at an intensity sufficient to mask the response to the 65-dB speech sounds and subsequently low-pass filtered. The conditions were quiet (no masking), low-pass noise cutoff frequencies of 250, 500, 1000, 2000, and 4000 Hz, and broadband noise. RESULTS: As the cutoff frequency of the low-pass noise masker was raised, ERP latencies increased and amplitudes decreased. The low-pass noise affected N1 differently than the other ERP or behavioral measures, particularly for responses to 80-dB speech stimuli. N1 showed a smaller decrease in amplitude and a smaller increase in latency compared with the other measures. Further, the cutoff frequency where changes first occurred was different for N1. For 80-dB stimuli, N1 amplitudes showed significant changes when the low-pass noise masker cutoff was raised to 4000 Hz. In contrast, d', MMN, N2, and P3 amplitudes did not change significantly until the low-pass noise masker was raised to 2000 Hz. N1 latencies showed significant changes when the low-pass noise masker was raised to 1000 Hz, whereas RT, MMN, N2, and P3 latencies did not change significantly until the low-pass noise masker was raised to 2000 Hz. No significant differences in response amplitudes were seen across the hemispheres (electrode sites C3M versus C4M) in quiet, or in masking noise. CONCLUSIONS: These results indicate that decreased audibility, resulting from the masking, affects N1 in a differential manner compared with MMN, N2, P3, and behavioral measures. N1 indexes the presence of audible stimulus energy, being present when speech sounds are audible, whether or not they are discriminable. MMN indexes stimulus discrimination at a pre-attentive level. It was present only when behavioral measures indicated the ability to differentiate the speech sounds. N2 and P3 also were present only when the speech sounds were behaviorally discriminated. N2 and P3 index stimulus discrimination at a conscious level. These cortical ERP in low-pass noise studies provide insight into the changes in brain processes and behavioral performance that occur when audibility is reduced, such as with low frequency hearing loss.

Adult↗
PubMed2004

Effects of ascorbic acid on oxidative system and transient evoked otoacoustic emissions in rabbits exposed to noise.

OBJECTIVES/HYPOTHESIS: The objective was to investigate the effects of both noise exposure and ascorbic acid on oxidative status and hearing thresholds of rabbits. STUDY DESIGN: Randomized prospective animal study comparing oxidative parameters and otoacoustic emissions in two rabbit groups exposed to noise. One group was given ascorbic acid, the other group was not given any treatment. METHODS: Two groups of rabbits were used in the study; each group had six rabbits. The six rabbits in the first group were not given any treatment, whereas 500 mg intramuscular ascorbic acid twice daily for 2 1/2 days was given to the six rabbits in the second group. Transient evoked otoacoustic emissions were recorded in all animals before and after noise exposure. Total protein sulfhydryl groups, carbonyl contents, and malondialdehyde levels, as well as erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels, were measured in all rabbits. All the rabbits were exposed to noise (100 dB sound pressure level, 1000 Hz, 1 h), and transient evoked otoacoustic emissions were recorded again. RESULTS: When oxidative parameters before noise exposure were compared, erythrocyte glutathione and catalase enzyme levels were detected to be higher in the second group (P <.05). In the first group of rabbits after noise exposure, total protein sulfhydryl groups were found to be reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels were elevated significantly (P <.05). In this group, erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels were low (P <.05). In the second group, which was given ascorbic acid, total protein sulfhydryl groups were reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels did not change (P >.05) following noise exposure. In the second group, erythrocyte glutathione and catalase enzyme levels were reduced (P <.05), but superoxide dismutase levels did not change (P >.05). Transient evoked otoacoustic emissions after noise exposure were weak in both groups, but reproducibility and signal-to-noise ratios were higher in the second group (P <.05). CONCLUSION: Ascorbic acid treatment inhibited both lipid peroxidation and oxidative damage of proteins in rabbits exposed to noise. The study data suggest, at least, that oxidative status should be included in the physiopathology of noise-induced hearing loss; in addition, a brief application of ascorbic acid before noise exposure appeared to play a protective role for cochlea.

Animals↗
PubMed2001

Noise distribution of an incubator with nebulizer at a neonatal intensive care unit in southern Taiwan.

The purpose of this study was to investigate the noise distribution and sources of peak noise inside an incubator with a nebulizer at a neonatal intensive care unit of a medical center in Southern Taiwan. Sound levels were monitored continuously with an electronic sound-meter for 24 hours daily over a one-week period. Three working hours (day, evening, and night hours) in the weekday and weekend (total 48 hours) were selected randomly from the one-week period of noise survey to observe peak noise at levels > or = 65 dBA. Results revealed that 24.8% of the total monitoring period had sound levels at < or = 59 dBA, 58.9% at 60-64 dBA, 10.7% at 65-69 dBA, and 5.6% at > or = 70 dBA. Furthermore, a total of 947 peak noises > or = 65 dBA were found within the 48 hours, of which 61.5% were in a range of 65-69 dBA, 24% of 70-74 dBA, 9.8% of 75-79 dBA, and 4.8% > or = 80 dBA. Human-related sources, equaling 79%, were the dominant peak noises. These noises included opening and closing doors, banging the incubator hood, conversation among staff, nursing activity inside the incubator, tearing and opening paper or bags, opening and closing trash can lids, and bumping metal carts or other apparatus. Nonhuman-related sources were 21% including alarms of monitors and running of the incubator motor. Results of this study showed that the noise distribution in the incubator with nebulizer was far above a protective limitation of 58 dBA, suggested by the American Academy of Pediatrics in 1974. However, most peak noises could be reduced by modification of staff behavior. Therefore, determinations of noise distribution and sources of peak noise in this study are useful for further noise reduction programs.

Humans↗
PubMed1990

Level discrimination of frozen and random noise.

This paper examines how the difference limen for level, delta L, is affected by stimulus bandwidth and variability. The delta L's were measured in three normal listeners using an adaptive two-interval, forced-choice procedure. The 30-ms stimuli were a 3-kHz tone and nine noise bands with half-power bandwidths ranging from 50 Hz-12 kHz. Except for the 12-kHz bandwidth, which was a low-pass noise, the noise bands were centered at 3 kHz. The delta L's were measured for both frozen and random noises presented at 30, 60, or 90 dB SPL overall. For frozen noises, the same sample of noise was presented throughout a block of 50 trials; for the random noises, different samples of noise were used in each interval of the trials. Results show that the delta L's are higher for random than for frozen noises at narrow bandwidths, but not at wide bandwidths. The delta L's for frozen narrow-band noises decrease with increasing level and are similar to those for the pure tone, whereas the delta L's for wideband noises are only slightly smaller at 90 than at 30 dB SPL. An unexpected finding is that the delta L's are larger at 60 than at 30 dB SPL for both frozen and random noises with bandwidths greater than one critical band. The effect of bandwidth varies with level: The delta L's decrease with increasing bandwidth at low levels, but are nearly independent of bandwidth at 90 dB SPL. The interaction of bandwidth and level is consistent with the multiband excitation-pattern model, but the nonmonotonic behavior of delta L as a function of level suggests modifications to the model.

Acoustic Stimulation↗
PubMed1993

Complex noise exposures: an energy analysis.

Industrial noise environments usually present a complex stimulus to the exposed individual. These environments often contain mixtures of multiply reflected impact noises and a relatively Gaussian broadband noise. Noise exposure standards do not consider the possibility of interactions between the two classes of noise that can exacerbate the amount of hearing trauma. This paper presents the results of a large series of experiments designed to document the hazard posed to hearing from complex noise exposures. Twenty-three groups of chinchillas with 5 to 11 animals per group (total N = 135) were exposed for 5 days to either octave bands of noise, impacts alone, or combinations of impact and octave bands of noise. Evoked potential measures of hearing thresholds and cochleograms were used to quantify the noise-induced trauma. The results show that, for sound exposure levels (SEL) which produce less than approximately 10 dB PTS (permanent threshold shift) or 5% total sensory cell loss, equal-energy exposures tend to produce equivalent effects on hearing. However, there is a range of at least 10 dB in the SEL parameter where hearing loss from equal-energy exposures at a particular SEL can be exacerbated by increasing the repetition rate of the impacts or by the addition of a Gaussian low-level noise. The exacerbation of trauma from the addition of a Gaussian continuous noise is dependent upon the spectrum of that noise.

Acoustic Stimulation↗