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PubMed1985

Representation of tones in noise in the responses of auditory nerve fibers in cats. I. Comparison with detection thresholds.

Rate and temporal responses evoked by 1-kHz or 8-kHz tones in continuous broadband noise are described for large populations of auditory nerve fibers in anesthetized cats. The signal-to-noise ratios (S/Ns) of the tone and noise stimuli were above behavioral detection thresholds. Stimulus combinations were presented (1) over a range of moderate to high noise intensities at a constant S/N and (2) using high intensity noise and varying S/N. Responses of low (less than 1 spike/sec) and medium (1 to 19 spikes/sec) spontaneous rate (SR) fibers were compared with those of high SR (greater than 19 spikes/sec) fibers. Low and medium SR fibers with best frequencies in the region of the test tone frequency exhibited tone-evoked rate changes at all sound levels tested. High SR fibers, in contrast, exhibited much weaker tone-evoked rate changes at the lowest noise level tested. In the presence of high intensity noise, high SR fibers did not exhibit tone-evoked rate changes due to saturation by the noise. Fibers with best frequencies in the region of 1 kHz also exhibited strong phase-locking to the 1 kHz tone which increased as the tone level increased but which did not differ for the various SR groups. Results suggest that information in the rate responses of low and medium SR fibers can account for the encoding of information about tones in noise by the nervous system.

Animals↗
PubMed1982

Cardiovascular effects of noise.

The purpose of this study was to evaluate the acute hemodynamic and hormonal effects induced by short-term exposure to loud noise in man. Loud noise (95 dBA or 100 dBA) caused an increase in blood-pressure in healthy normotensive subjects as well as in patients with essential hypertension. The blood pressure elevation was caused by vasoconstriction in patients with essential hypertension and in normotensive subjects with a positive family history of hypertension, while the blood pressure response in normotensive subjects without a family history of hypertension was due mainly to an increase in cardiac output. This might indicate that there are genetically determined differences in the cardiovascular response to noise. Stimulation with noise did not increase plasma levels of catecholamines, prolactin, cortisol or growth in normotensive subjects. In patients with essential hypertension plasma noradrenalin increased, while plasma adrenalin and plasma renin activity did not change. The increase in diastolic blood pressure caused by loud noise was not affected by beta 1-selective or non-selective beta-adrenoceptor blockade, nor was it changed by alpha 1-or combined alpha 1-and non-selective beta-adrenoceptor blockade. The elevation in blood pressure induced by noise is usually mediated by vasoconstriction, i.e. an alpha 1-effect. When alpha 1-adrenoceptors are blocked, the blood pressure response to noise is mediated by an increase in cardiac output, i.e. a beta-adrenoceptor mediated effect. It thus seems as if an increased pressure is essential during exposure to loud noise. If one part of the sympathetic nervous system is blocked, other parts can be activated in order to preserve the blood pressure on an elevated level. This indicates a temporary resetting of the baroreceptors during exposure to noise, which probably is mediated from the hypothalamus.

Adrenergic beta-Antagonists↗
PubMed1984

The behavioral effects of noise on man: the patient with "intensive care unit psychosis".

Alterations in the behavior of a critically ill patient, commonly referred to as ICU psychosis, may result from the physiological stresses incurred by these patients compounded by disruptions from environmental noises. Research has demonstrated that noise levels can greatly affect sleep stage progression as well as the frequency of awakenings in normal subjects during brief testing sessions. Furthermore, the ability to solve problems and tolerate frustration decreases when persons are exposed to noise. Clinical research studies have reported the excessive noise levels in everyday ICU equipment and procedures, such as hypothermia blankets, ventilators, and intermittent positive pressure breathing. Yet when patients were polled about the most disturbing noises, staff conversations and personnel activity were ranked among the highest. In addition, a direct relationship between level of noise and the amount of pain medication administered to patients was reported. Recommendations for the elimination of most noise within an ICU were personnel related. Being more cognizant of conversational topics and noise levels could greatly reduce the patient's level of irritability and feelings of impersonalization. Specific issues regarding current practice, staff behavior, and structural design were addressed. Thus familiarity with behavioral and clinical research regarding noise and its effect on man's behavior can serve as a guideline to the improvement of the quality of care that the critically ill patient receives.

Behavior↗
PubMed1994

Impact of statutory medical examinations on control of noise-induced hearing loss.

Noise at work is ubiquitous and presents a major occupational health problem in many countries. Prolonged exposure to loud noise can cause deafness of varying degrees. This is insidious in the early stages, but can be detected by audiometric examination. In the prevention of noise-induced hearing loss, control of noise at its source would be ideal. But for practical purposes, a multipronged approach is often necessary. Every noisy workplace should set up an in-plant Hearing Conservation Programme (HCP) which includes periodic audiometric examination of workers. In Singapore, since 1985, workers in many noisy workplaces are required to undergo statutory pre-employment and annual audiometric examinations arranged by their employers. The examinations are carried out by Designated Factory Doctors who have undergone a course of training in occupational health and are registered with the Labour Ministry. The doctors' role includes advising workers and employers on the prevention of noise-induced deafness (NID). Doctors notify cases of NID to the Ministry of Labour which conducts investigations where indicated. Since NID is insidious, workers with the condition would not be detected in the early stages without an audiometric examination. With the introduction of the statutory examinations, more noise-exposed workers were examined and cases of early hearing impairment picked up. The statutory medical examinations have helped to highlight the problem of the noise hazard. Individual companies are able to monitor the noise problem in their workplaces, using the audiometric results to supplement the noise assessments. Susceptible workers can be identified and followed up more closely, and health education intensified.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry↗
PubMed1993

[Use of a Ca(++) antagonist in noise-induced hearing loss in animal experiment].

Hearing thresholds at 1-2-4-6 and 8 kHz were determined by brainstem evoked response audiometry (BERA) in 24 guinea pigs. The animals were then divided into 6 groups. Group 1 (controls) received no drugs and were not exposed to noise. Group 2 were given 15 mg/24 h/kg diltiazem s.c. for 13 days. Group 4 was exposed to the same noise as group 3 but was also treated with diltiazem 15 mg/kg/24 h from three days before noise exposure until the end of the experiment. Group 5 was exposed to a 110 dB SPL broad-band noise for 3 h daily for 10 days. Group 6 was exposed to the same noise as group 5 and was treated with diltiazem 15 mg/kg/24 h from three days before noise exposure until the end of the experiment. After the last noise exposure hearing thresholds were determined again by BERA and were found to be unchanged in those animals treated with the drug alone and the controls. In those groups with drug administration and noise exposure hearing loss was less than in the animals exposed to noise alone. This difference was more pronounced in the 90 dB groups than in the 110 dB groups.

Acoustic Stimulation↗
PubMed1996

Noise emission zones in an automobile sheet-metal pressing plant, a 25-year follow-up study at three locations in the plant.

The Volvo plant at Olofström, Sweden is engaged in the pressing and assembling of sheet-metal components for automobiles. During the past 25 years, determined efforts have been made to introduce less noisy methods of production and to limit the levels of noise emission in three large workshops at the plant. Noise levels were mapped with the aid of stationary noise measurements. The results are expressed in terms of noise emission zones and presented as noise contour maps. The investigations were made on four occasions between 1967 and 1991. Following the comparative area calculations of the noise emission zones, it was deduced that the noise levels had been significantly reduced, despite an increased production. The results show that noise reduction measures applied to the presses. An increase in automation in sheet-metal handling, improved quality in the pressing of components and changes in the range of products have contributed to the reduction of noise levels at the plant.

Automobiles↗
PubMed2000

Air blast circuit breaker noise and hearing loss: a multifactorial model for risk assessment.

The assessment of the risk to hearing from impulse noise exposure may be a problem for the occupational physician because existing legislative and international noise exposure standards deal primarily with continuous noise, and are not valid in excess of the peak exposure limit of 200 pa (140 dB). Noise exposure in excess of this level, for example that due to firearms, is frequently perceived as harmful, but this is not necessarily the case, as impulse noise standards do, in fact, allow exposure with a maximum in the order of 6.3 kPa (170 dB). To illustrate this, a cross-sectional group of electrical transmission workers have been studied who were exposed to significant levels of impulse noise from air blast circuit breakers and firearms. Important hearing loss factors have been identified by means of a specially designed questionnaire. Using the Health & Safety Executive definition, the risk of hearing loss was determined by calculating prevalence odds ratios (ORs) for exposure to these factors. The OR for those with fewer than eight unprotected air blast circuit breaker exposures was 2.27 (95% confidence interval (CI), 1.01-5.08), whilst for those with more than eight exposures the OR was 2.10 (95% CI, 0.97-4.54). For firearm exposure, ORs of 1.61 (95% CI, 0.95-2.74) were noted in the medium exposure group and 2.05 (95% CI, 1.08-3.86) in the high exposure group. When all the factors were included in the model, the most significant factor was age. The study gives support to the impulse noise exposure criteria, confirming the borderline risk from air blast circuit breaker noise exposure and the relative safety of moderate gunfire exposure.

Adult↗
PubMedDate not supplied

Intermittent exposure to noise: effects on hearing.

Most studies of the effects of noise upon hearing have dealt with continuous noise exposure. Previous reports on intermittent exposure to noise concluded that it causes less damage to hearing than does continuous exposure to noise of the same intensity. In this investigation, 12,000 workers were screened to find 295 subjects who met the strict criteria of the study. Most of the subjects were exposed to jackhammer noise at peak levels of 118 dBA. Intermittent exposure to intense noise results in very severe loss in high frequencies but relatively little or no hearing loss in the lower frequencies even after many years of exposure. This differs substantially from the effects of continuous exposure to noise of the same intensity. It remains to be determined whether this pattern of hearing results from intermittent exposure to all sorts of noise or only from the kinds of sources investigated in this study.

Adult↗
PubMed2005

[Combined exposure to noise and vibration and its effects on workers' hearing].

OBJECTIVE: To assess the exposure of bus drivers to noise and whole-body vibration (WBV) and to examine the possibility of an association between these risk factors for noise-induced hearing loss. METHODS: A cross-sectional study was carried out among 141 bus drivers who underwent an audiometry test. This group was classified and internally stratified in subgroups of "exposed" and "controls" according to cumulative working time as bus drivers. Their exposure to noise and vibration was assessed. The association between noise-induced hearing loss (NIHL) and the set of explanatory variables was analyzed through logistic regression. RESULTS: The average (+/- standard deviation) weekly noise exposure of front-engine bus drivers was 83.6 +/- 1.9 dB(A), while rear-engine bus drivers were exposed to 77.0 +/- 1.1 dB(A). The weighted average of vibration acceleration was 0.85/m(2). In the best adjusted model, the multivariable analysis showed that age (>44; OR=2.54; 95% CI=1.15-5.62), diabetes (OR=5.46; 95% CI=0.95-31.4), and the level of noise emission [>86.8 dB(A); OR=2.76; 95% CI=1.24-6.15] were risk factors for NIHL. In another model studied, WBV exposure was significant in determining NIHL. CONCLUSIONS: Bus drivers were exposed to significant WBV levels. The noise exposure was more pronounced in front engine than in rear-engine vehicles. No association between WBV exposure and NIHL was observed and no interaction was found between WBV and noise exposure. Further studies are required as other model indicated an association between WBV and NIHL.

Audiometry↗
PubMed1979

Speech intelligibility in and speech interference levels of traffic noise in hearing-impaired and normal listeners.

Speech intelligibility (phonetically balanced monosyllables = PB words) in traffic-like noise (random noise) as well as the speech interference levels (75% intelligibility) of this noise were investigated in three common listening situations, two indoors and one outdoors. A total of 279 persons were examined; 56 had normal hearing, 90 a presbycusic-type hearing loss, 95 noise-induced hearing loss, and 38 conductive hearing loss. In the indoor situation the hearing-impaired groups mainly retained their intelligibility in 40 dBA. Lowering of the noise level to less than 40 dBA resulted in only a minor, mostly insignificant improvement in speech intelligibility. Normal-hearing listeners maintained good speech intelligibility in the outdoor listening situation with noise levels up to 60 dBA, without lip-reading. For hearing-impaired groups, representing more than 1/2 million (8% of the population) people in Sweden, with hearing loss due to age and/or noise, the noise level outdoors must be lowered to 45 dBA in order to achieve good speech intelligibility at 1 m, without lip-reading.

Adolescent↗
PubMedDate not supplied

[Noise and communal dining facilities].

Noise is a sound which is unwanted, either because of its effect on humans, its effect on fatigue or multifunctions of physical equipment, or its interference with the perception or detection of other sounds. It is a part of environmental pollution which can, in certain circumstances, reach worrying levels for the population (130 dB cause pain). Unsuitable exposure to noise for even short periods of time is responsible for symptomology involving the hearing organs (hypoacusis) and other parts of the body such as the cardiovascular, muscular and digestive systems via the connection between the central and the autonomous nervous systems. Noise in communal eating areas can be classed as coming from 3 sources: 1) operation of cooking machinery; 2) banging of pans and equipment; 3) voices of both staff and diners. The intensity of noise on these premises varies generally between 60 and 80 dB (discomfort threshold). The Regulations governing this subject are D.Lgs n.277 of 15/8/1991 regarding the protection of employees, D.P.C.M. of 1/3/1991 which establishes the maximum levels of noise both in the home and outside, and the more recent D.P.C.M. of 21/5/1999 referring to noise in public places, which includes restaurants. To contain the exposure to noise in public eating places, we believe that action should be taken at legal levels with stricter limits than the recently passed level of 105 dB, in the building planning departments and also with technological intervention in order to reduce the effects that noise has on the auditive and extra-auditive organs and thus limit possible sublimal messages which certainly do not benefit the psycho-physical well-being of the diners.

Cooking↗
PubMed2006

[Distortion product otoacoustic emissions before and after one year exposure to impulse noise].

INTRODUCTION: Firearms are a common source of impulse noise that may be very harmful to the auditory organ. Impulse noise from weapons and explosions continually produces hearing damage among military personnel. The discovery of otoacoustic emission (OAE) has given a new possibility of early diagnosis of noise induced hearing loss. The transiently evoked otoacoustic emission (TEOAE) and distortion product otoacoustic emission (DPOAE) are non-invasive, objective and frequency specific audiometric tests for evaluating outer hair cell function. The aim of the study was to asses the effects of exposure to impulse noise on DPOAE after one year of the obligatory military service. MATERIAL AND METHODS: The study comprised 92 (184 ears) soldiers, subjected to impulse noise during military service. The examine group was divided according total noise exposure. The control group consisted of secondary school students not exposed to noise. DPOAE was recorded before and after one year of military service. RESULTS: After military service significant deterioration of DPOAE level was observed at frequencies of 1, 3, and 4 kHz on the right ear and 2, 5 and 6 kHz left one. CONCLUSIONS: 1. Reduction of DPOAE amplitude connected all frequencies. 2. We did not notice significant differences between groups connected total noise exposure.

Adult↗
PubMed1987

Diabetes, noise exposure, and hearing loss.

To examine the relationship of diabetes, noise exposure, and hearing loss, the authors reanalyzed data from a cross-sectional investigation on noise exposure, hearing loss, and BP conducted in a high-noise and a low-noise plant. Twenty-eight of 348 participants met the following criteria for diabetes: (1) currently on insulin or oral hypoglycemics or (2) at least two elevated serum glucose levels despite adhering to a calorie-restricted diet. Diabetics were evenly distributed between high- and low-noise exposure. A two-way analysis of variance was conducted at each of seven hearing threshold frequencies using diabetes and high-noise exposure as main effects. Diabetics demonstrated no evidence of higher hearing threshold shifts than nondiabetics at the same noise levels. Noise and diabetes together do not appear to produce more neuropathic damage than does one insult alone.

Adult↗
PubMed1984

[Effect of noise and other factors damaging to hearing on hearing loss].

The goal of the present paper was to investigate the relationship between hearing loss and noise exposure. Moreover, the author also examined the question whether damaging factors detected in the case history (hereditary susceptibility, toxic and infectious-toxic factors, cerebral and acoustic trauma, war, tinnitus) and working conditions (ototoxic industrial substances, shift work, hearing protection) affect hearing loss in any way. A tone and speech audiogram of 1020 persons exposed to industrial noise in a power station and non-exposed persons was evaluated for this purpose. In addition to exposure at the respective place of work, the sound intensity and total period of employment were also taken into consideration. The noise exposure of the persons working in industrial noise exceeded the limits of hearing damage, although it generally amounted to levels of less than 95 dB (A). Hearing loss in persons exposed to industrial noise increases as the noise level increases. In the intensities we examined, however, the level of sound appears to be less decisive in its effect than generally assumed. The effect of time on the threshold of hearing, on the other hand, is of importance at evaluation levels of less than 90 dB (A). In addition to age and occupational noise exposure, the following factors are significantly correlated to the threshold of hearing: hereditary susceptibility, traumata, war, tinnitus and shift work. On the whole, the factors and working conditions recorded in the case history have a considerable effect on hearing loss and are approximately equivalent to the noise at sound levels up to about 90 dB (A).

Adolescent↗
PubMed1981

Noise analysis of the K+ current through the apical membrane of Necturus gallbladder.

Current noise power spectra of the voltage-channel (V = 0) Necturus gallbladder, exposed to NaCl-Ringer's on both sides contained a relaxation noise component, which overlapped with a 1/f alpha noise component, with alpha being about 2. Substitution of all Na+ by K+ on either the serosal or mucosal side increased the relaxation as well as the 1/f alpha noise component considerably. In Necturus gallbladder both noise components are reduced by addition of 10 mM, 2,4,6-triaminopyrimidine (TAP) or 5 mM BA2+ to the mucosal side, as well as by acidification of the mucosal solution to pH 5 and lower. Five mM of tetraethylammonium (TEA+) added to the mucosal solution, abolished K+ relaxation noise and decreased the 1/f alpha noise component. Applying a Cs+ concentration gradient across the epithelium did not yield relaxation noise. However, if Rb+ was substituted for all Na+ on one side, a Lorentzian noise component appeared in the spectrum. Its plateau was smaller than with KCl-Ringer's on the respective side. These data confirm the existence of fluctuating K+ channels in the apical membrane of the Necturus gallbladder. Furthermore it can be concluded that these channels have the permeability sequence K+ greater than Rb+ greater than Cs+. The inhibition of the fluctuations by mucosal acidification indicates the existence of acidic sites in the channel. The single-channel conductance was estimated to be between 6.5 and 40 pS.

Animals↗
PubMed1981

Noise analysis of the K+ current through the apical membrane of Necturus gallbladder.

Current noise power spectra of the voltage-clamped (V = 0) Necturus gallbladder, exposed to NaCl-Ringer's on both sides contained a relaxation noise component, which overlapped with a 1/f alpha noise component, with alpha being about 2. Substitution of all Na+ by K+ on either the serosal or mucosal side increased the relaxation as well as the 1/f alpha noise component considerably. In Necturus gallbladder both noise components are reduced by addition of 10mM 2,4,6-triaminopyrimidine (TAP) or 5 mM of tetraethylammonium (TEA+) added to ification of the mucosal solution to pH 5 and lower. Five mM of tetraethylammonium (TEA+) added to the mucosal solution, abolished K+ relaxation noise and decreased the 1/f alpha noise component. Applying a Cs+ concentration gradient across the epithelium did not yield relaxation noise. However, if Rb+ was substituted for all Na+ on one side, a Lorentzian noise component appeared in the spectrum. Its plateau was smaller than with KCl-Ringer's on the respective side. These data confirm the existence of fluctuating K+ channels in the apical membrane of the Necturus gallbladder. Furthermore it can be concluded that these channels have a permeability sequence K+ greater than Rb+ greater than Cs+. The inhibition of the fluctuations by mucosal acidification indicates the existence of acidic sites in the channel. The single-channel conductance was estimated to be between 6.5 and 40 pS.

Animals↗
PubMed2001

Noise-induced transition in excitable neuron models.

We studied the influence of noisy stimulation on the Hodgkin-Huxley neuron model. Rather than examining the noise-related variability of the discharge times of the model--as has been done previously--our study focused on the effect of noise on the stationary distributions of the membrane potential and gating variables of the model. We observed that a gradual increase in the noise intensity did not result in a gradual change of the distributions. Instead, we could identify a critical intermediate noise range in which the shapes of the distributions underwent a drastic qualitative change. Namely, they moved from narrow unimodal Gaussian-like shapes associated with low noise intensities to ones that spread widely at large noise intensities. In particular, for the membrane potential and the sodium activation variable, the distributions changed from unimodal to bimodal. Thus, our investigation revealed a noise-induced transition in the Hodgkin-Huxley model. In order to further characterize this phenomenon, we considered a reduced one-dimensional model of an excitable system, namely the active rotator. For this model, our analysis indicated that the noise-induced transition is associated with a deterministic bifurcation of approximate equations governing the dynamics of the mean and variance of the state variable. Finally, we shed light on the possible functional importance of this noise-induced transition in neuronal coding by determining its effect on the spike timing precision in models of neuronal ensembles.

Action Potentials↗
PubMed1976

The contribution of communications signals to noise exposure.

Man-mounted miniature recording equipment has been used to measure the electroacoustic conditions obtaining in cockpits of aircraft and at the pilot's ear during operational sorties in the Royal Air Force. Although this paper considers the measurements taken that relate to the total noise exposure (noise dose) received by aircrew, the results apply equally to anyone who is exposed to high noise and requires communications. Comparison of the noise at the ear with the cockpit noise gave a measure of headgear attenuation which was used to adjust a [Formula: see text] filter. Playing cockpit noise tapes through this filter to a noise dose meter gave the noise dose that would have been experienced had there been no communications signals. The results showed that the communications signals at the ear, averaging 40% of the sortie time, are a major contributor to the total dose, and, without the signals, the dose averaged about 6 dB less. In view of the Health and Safety at Work Act, 1974, employers should be aware of the additional dose to which employees are exposed because of communications. A method for the prediction of noise dose is proposed where communication takes place in a noisy environment.

Journal Article↗