Noise Induced Hearing Loss

Exposure to loud noise continues to be the largest cause of hearing loss in the adult population. The problem of NIHL impacts a number of disciplines. US standards for permissible noise exposure were originally published in 1968 and remain largely unchanged today. Indeed, permissible noise exposure for US personnel is significantly greater than that allowed in numerous other countries, including for example, Canada, China, Brazil, Mexico, and the European Union. However, there have been a number of discoveries and advances that have increased our understanding of the mechanisms of NIHL. These advances have the potential to impact how NIHL can be prevented and how our noise standards can be made more appropriate.

In the Occupational Safety and Health Act of 1970, Congress declared that its purpose was to assure, so far as possible, safe and healthful working conditions for every working man and woman and to preserve our human resources. In this Act, the National Institute for Occupational Safety and Health (NIOSH) is charged with recommending occupational safety and health standards and describing exposure concentrations that are safe for various periods of employment-including but not limited to concentrations at which no worker will suffer diminished health, functional capacity, or life expectancy as a result of his or her work experience. By means of criteria documents, NIOSH communicates these recommended standards to regulatory agencies (including the Occupational Safety and Health Administration [OSHA]) and to others in the occupational safety and health community. Criteria documents provide the scientific basis for new occupational safety and health standards. These documents generally contain a critical review of the scientific and technical information available on the prevalence of hazards, the existence of safety and health risks, and the adequacy of control methods. In addition to transmitting these documents to the Department of Labor, NIOSH also distributes them to health professionals in academic institutions, industry, organized labor, public interest groups, and other government agencies. In 1972, NIOSH published Criteria for a Recommended Standard: Occupational Exposure to Noise, which provided the basis for a recommended standard to reduce the risk of developing permanent hearing loss as a result of occupational noise exposure [NIOSH 1972]. NIOSH has now evaluated the latest scientific information and has revised some of its previous recommendations. The 1998 recommendations go beyond attempting to conserve hearing by focusing on preventing occupational noise-induced hearing loss (NIHL). This criteria document reevaluates and reaffirms the recommended exposure limit (REL) for occupational noise exposure established by the National Institute for Occupational Safety and Health (NIOSH) in 1972. The REL is 85 decibels, A-weighted, as an 8-hr time-weighted average (85 dBA as an 8-hr TWA). Exposures at or above this level are hazardous. By incorporating the 4000-Hz audiometric frequency into the definition of hearing impairment in the risk assessment, NIOSH has found an 8% excess risk of developing occupational noise-induced hearing loss (NIHL) during a 40-year lifetime exposure at the 85-dBA REL. NIOSH has also found that scientific evidence supports the use of a 3-dB exchange rate for the calculation of TWA exposures to noise. The recommendations in this document go beyond attempts to conserve hearing by focusing on prevention of occupational NIHL. For workers whose noise exposures equal or exceed 85 dBA, NIOSH recommends a hearing loss prevention program (HLPP) that includes exposure assessment, engineering and administrative controls, proper use of hearing protectors, audiometric evaluation, education and motivation, recordkeeping, and program audits and evaluations. Audiometric evaluation is an important component of an HLPP. To provide early identification of workers with increasing hearing loss, NIOSH has revised the criterion for significant threshold shift to an increase of 15 dB in the hearing threshold level (HTL) at 500, 1000, 2000, 3000, 4000, or 6000 Hz in either ear, as determined by two consecutive tests. To permit timely intervention and prevent further hearing losses in workers whose HTLs have increased because of occupational noise exposure, NIOSH no longer recommends age correction on individual audiograms.

The brain is the most complex organ in our body. Indeed, it is perhaps the most complex structure we have ever encountered in nature. Both structurally and functionally, there are many peculiarities that differentiate the brain from all other organs. The brain is our connection to the world around us and by governing nervous system and higher function, any disturbance induces severe neurological and psychiatric disorders that can have a devastating effect on quality of life. Our understanding of the physiology and biochemistry of the brain has improved dramatically in the last two decades. In particular, the critical role of cations, including magnesium, has become evident, even if incompletely understood at a mechanistic level. The exact role and regulation of magnesium, in particular, remains elusive, largely because intracellular levels are so difficult to routinely quantify. Nonetheless, the importance of magnesium to normal central nervous system activity is self-evident given the complicated homeostatic mechanisms that maintain the concentration of this cation within strict limits essential for normal physiology and metabolism. There is also considerable accumulating evidence to suggest alterations to some brain functions in both normal and pathological conditions may be linked to alterations in local magnesium concentration. This book, containing chapters written by some of the foremost experts in the field of magnesium research, brings together the latest in experimental and clinical magnesium research as it relates to the central nervous system. It offers a complete and updated view of magnesiums involvement in central nervous system function and in so doing, brings together two main pillars of contemporary neuroscience research, namely providing an explanation for the molecular mechanisms involved in brain function, and emphasizing the connections between the molecular changes and behavior. It is the untiring efforts of those magnesium researchers who have dedicated their lives to unraveling the mysteries of magnesiums role in biological systems that has inspired the collation of this volume of work.

The Institute of Medicine carried out a study mandated by Congress and sponsored by the Department of Veterans Affairs to provide an assessment of several issues related to noise-induced hearing loss and tinnitus associated with service in the Armed Forces since World War II. The resulting book, Noise and Military Service: Implications for Hearing Loss and Tinnitus, presents findings on the presence of hazardous noise in military settings, levels of noise exposure necessary to cause hearing loss or tinnitus, risk factors for noise-induced hearing loss and tinnitus, the timing of the effects of noise exposure on hearing, and the adequacy of military hearing conservation programs and audiometric testing. The book stresses the importance of conducting hearing tests (audiograms) at the beginning and end of military service for all military personnel and recommends several steps aimed at improving the military services' prevention of and surveillance for hearing loss and tinnitus. The book also identifies research needs, emphasizing topics specifically related to military service.

In September 1985, NATO sponsored an Advanced Study WOl'kshop entitled, "Noise-Induced Hearing Loss: Basic and Applied Aspects." Tne meeting was held in a mountain retreat near Lucca, Italy and was attended by scientists, clinicians, and public officials from 12 countries. This was the third in a series of such conferences organized by the authors. The first two were supported by the United States National Institute of Occupational Safety and Health; their proceedings were published as "The Effects of Noise on Hearing" in 1976 and "New Perspectives on Noise-Induced Hearing Loss" in 1982. The Organizing Committee approached NATO because it was felt that the problem of noise was common to all industrialized countries and was an especially serious problem for the military. Thus, the NATO sponsorship and the Italian site of the meeting were part of the Organizing Committee's plan to obtain an international and thorough repr'esentation on the problem of noise-induced hearing loss. The NATO meeting and proceedings followed the format of the previous two symposia with an initial focus on the anatomical and physiological disturbances resulting from noise-induced hearing loss. This was followed by sections devoted to studies of a more applied nature involving general auditory performance in noise, issues associated with the establishment of noise-exposure criteria, nonauditory effects of noise, and the interaction of noise with other agents.

After the early success of some articles as author and co-author, Dr Win Tin has come up with his first book on Noise-Induced Hearing Loss and the Hidden Society Burden. He noticed that everyone needs peace of mind, especially after a long working day. We need to rest, physically and mentally to recoup, working again with enthusiasm the next day. Thus, it is important that we have a certain private, quiet, peaceful serene environment, day or night. But noise is all around us. The sound of grass cutters, the piling of structures nearby, children playing and shouting, or the traffic noise. These can make a lot of noise and the peace shattered. Noise-induced hearing loss is mainly caused by a certain amount of noise which has a deleterious effect on the ear when exposed to long periods of time e.g. years, and usually without the person noticing, as in occupational noise-induced hearing loss or single instances of extreme noise, as in acoustic trauma. This causes not only hearing loss but effects socially, financially, physically and mentally. Its problem is so big with compensation in millions, causing a huge hidden burden to the society, people and government. Yet it should be noted that this is the only preventable cause of sensorineural hearing loss, which can be prevented, while other causes are still not possible. The book introduces various noise, the pathogenesis and causes of noise-induced hearing loss, as seen in various strata of people. Apart from this, there is the Malaysian perspective as written by some researchers from Malaysia. Then there are also effects of noise not only on humans but also in birds and fish. Methods to diagnosis and ways to prevent, with up-to-date researches and treatment are also discussed. Thus, it is a comprehensive one for the knowledge of all levels, professionals and non-professionals. This book is important, and everybody should read or keep as a reference, as they will know in-depth, as most are unaware of the hidden problem. Young people, military, hospital workers, nurses, contractors, builders, architect, engineers, urban planners, public health doctors and everyone can benefit from this book. Hence, this book is useful not only for leisure reading but cherished for life. With the 25th anniversary of UMS, this book can be a milestone, for the wellness of UMS staff and people of Sabah.

The collection of systems represented in this volume is a unique effort to reflect the diversity and utility of models used in biomedicine. That utility is based on the consideration that observations made in particular organisms will provide insight into the workings of other, more complex systems. This volume is therefore a comprehensive and extensive collection of these important medical parallels.