Permanent Hearing Threshold Shift Research Articles

Protective effects of magnesium on noise-induced hearing loss: Animal studies

Magnesium (Mg) deficiency was found to increase noise-induced hearing loss in laboratory animals. This paper reports both prophylactic and therapeutic effects of Mg on the acoustic trauma produced by a high-level impulse noise series (Lpeak 167 dB, 38 min, 1/s). Hearing loss was tested by auditory brainstem response audiometry at frequencies between 0.5 and 32 kHz. Permanent hearing threshold shifts (PTS) were measured 1 week after the exposure. For the prophylaxis experiments, anesthetized guinea pigs with either a physiologically high or low Mg status, produced by different diets, were used. For the therapy experiments, animals with the low Mg status received (immediately after exposure) either Mg injections combined with a Mg-rich diet or saline as a placebo. Total Mg concentrations of perilymph, cerebrospinal fluid, and plasma were analyzed to test the Mg status of the animals. The PTS was found to be significantly lower in the high-Mg group than in the low-Mg group. This also applies to the PTS found between the therapy and the placebo groups. There was a good correlation between the PTS and the perilymphatic Mg. The intracochlear Mg level seems to play an important role in the acoustic trauma. [Supported by German Defence Ministry.]

Prolonged Exposure to Industrial Noise: Cochlear Pathology does not Correlate with the Degree of Permanent Threshold Shift, but is Related to Duration of Exposure

Prolonged Exposure to Industrial Noise: Cochlear Pathology does not Correlate with the Degree of Permanent Threshold Shift, but is Related to Duration of Exposure: Mariola Śliwińska‐Kowalska, et al. Department of Physical Hazards, The Nofer Institute of Occupational Medicine—It has been shown that the damaging effects of noise on the mammalian inner ear strongly depend upon parameters of exposure, such as the intensity of noise, the duration of exposure, etc., but the relationship between permanent hearing loss and cochlear damage still remains unclear. In this study, we were interested in the damaging effects of exposure to typical steady‐state, wide‐band industrial noise acting for as long as 12 weeks on guinea pigs. The aim of the study was to evaluate the relationships among the duration of exposure to industrial noise, the level of permanent hearing loss and the degree of cochlear injury and to assess the possible mechanisms of industrial noise‐induced hearing loss. The results of the study indicate that 1) prolonged exposure to industrial noise causes in guinea pigs a relatively fast increase in permanent hearing threshold shift (PTS) up to 30 dB, which reaches the asymptotic level after 4 weeks of exposure; 2) the first 30 dB of PTS is caused almost exclusively by the damage to outer hair cells; 3) the degree of cochlear damage is not related to the level of permanent threshold shift; 4) the progression in cochlear pathology depends upon the duration of exposure; 5) both micromechanical and metabolic mechanisms seem to be involved in the development of industrial noise‐induced hearing loss.

Oral magnesium intake reduces permanent hearing loss induced by noise exposure

Introduction: Following animal experiments where correlations were observed between serum magnesium level and noise-induced permanent hearing threshold shifts (NIPTS), we tested the prophylactic effect of magnesium in human subjects exposed to hazardous noise. Methods: Subjects were 300 young, healthy, and normal-hearing recruits who underwent 2 months of basic military training. This training necessarily included repeated exposures to high levels of impulse noises while using ear plugs. During this placebo-controlled, double-blind study, each subject received daily an additional drink containing either 6.7 mmol (167 mg) magnesium aspartate or a similar quantity of placebo (Na-aspartate). Results: NIPTS was significantly more frequent and more severe in the placebo group than in the magnesium group, especially in bilateral damages. NIPTS was negatively correlated to the magnesium content of blood red cells but especially to the magnesium mononuclear cells. Long-term additional intake of a small dose of oral magnesium was not accompanied by any notable side effect. Concluslon: This study may introduce a significant natural agent for the reduction of hearing damages in noise-exposed population.

Annoyance and health risk caused by military low-altitude flight noise

Effects of noise of low-flying military jet aircraft were investigated from demoscopic and epidemiological points of view. Areas with different low-altitude flight noise exposure were compared with one another as to subjective annoyance, casual blood pressure and ear symptoms. With the same energy equivalent sound pressure level (Leq), the subjective disturbance caused by military low-altitude flight noise was essentially greater than that due to ordinary flight noise (in the neighbourhood of civil airports). A comparison of several areas revealed that frequencies of ear symptoms (tinnitus lasting more than one hour and permanent hearing threshold shifts of greater than 30 dB) were higher only in areas where maximal flight noise levels considerably exceeded 115 dB (A) accompanied by rapid noise level increases. Blood pressure measurements yielded significantly higher values (group difference 9 mm Hg systolic) in girls living in these highly exposed areas. Acoustic limits are proposed with respect to public health.

Current harmonics and acoustic noise in AC adjustable-speed drives

AC adjustable-speed drives (ASDs) are finding increased opportunities for applications in which acoustic noise is a major consideration for acceptability. The major source of noise in an ASD is the excitation of the motor by nonsinusoidal currents. For load characteristics that simulate the performance required for fans and compressors, ASDs based on induction motors, permanent-magnet motors, and switched reluctance motors have been examined for correlation between current and acoustic noise. The effects that the specific types of noise produced by drives have on human subjects is examined with regard to temporary and permanent hearing-threshold shifts.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of the potential association between noise‐induced hearing loss and cardiovascular evaluation in aircrew members

In recent years, many studies focused on noise exposure and its potential relationship to different measures of cardiovascular function. Several investigations reported significant correlations between hearing loss and certain cardiovascular parameters while others reported no relationships at all. Most evaluations have been retrospective in nature and as a consequence may include data which lack completeness or reliability, especially in the definition of noise exposure. Ascribing chronic medical consequences to noise exposure poses serious implications for individuals who are exposed to noise in work and leisure time environments. The present study explored the correlation between cardiovascular evaluation and noise‐induced hearing loss in medical records of 2250 aircrew members referred to the Air Force School of Aerospace Medicine for clinical evaluations. Aircraft flying hours, as well as permanent hearing threshold shift were used as indices of noise exposure. No significant associations were found between hearing impairment and various cardiovascular parameters or pathologies. How our results can be extrapolated to different populations will be addressed. How our findings should be viewed in terms of other contradictory findings and in terms of future exploration will be presented.

A survey of communications in the high noise environment of Army aircraft

In Army aircraft, the noise environment consists of a continuous noise level comprised of a mixture of random (broadband) and periodic frequencies (the aircraft noise signature or “whine”) and in the case of gunships, transient high‐level noise bursts generated by the weapons systems. The noise environment reaching the aviator's ear is comprised of direct ambient noise penetration and communications systems processed noise (during periods of communications use, or “open mike operations”). The most insidious impact of the high noise levels is the long‐term permanent hearing threshold shift, or hearing loss, that the aviator may incur from his prolonged exposure to the aircraft's interior sound pressure levels. Improvement of speech intelligibility under all flight conditions will improve the aviator's effectiveness by reducing the number of transmission repetitions necessary to assure that a message is correctly conveyed, thus reducing the distraction level during critical mission phases. Reducing the ambient aircraft noise processed by the communications system will further improve speech intelligibility and reduce this particular increased noise contribution to pilot stress.

Noise-induced shifts in males and females for a battery of hearing tests

Sex-related differences in the effects of noise on humans have been reported in several areas including physiological reactions, sleep disturbance, and permanent hearing threshold shift. It has been suggested that economic, social, and cultural factors may combine to reduce the opportunity for women to be exposed to high-level occupational and recreational noises. However, this contaminant is absent from research into noise-induced temporary threshold shift (TTS), because the noise exposures are carefully controlled in the laboratory performance of TTS studies. Most research into sex-related differences in temporary, auditory noise-exposure effects have been limited to the examination of threshold phenomena only. In the present study, a variety of noise-induced hearing changes have been examined. Subjects were tested before and after a one-half hour noise exposure using an audiometric test battery that included measures of pure-tone threshold, loudness discrimination, tone-on-tone masking, and loudness and pitch measuring of tinnitus. Data were examined for sex-related differences in the magnitude and incidence of noise-induced shifts in these auditory tasks. Implications of these findings for hearing conservation and for modeling noise effects are discussed.