Vibroacoustic disease: the need for a new
attitude towards noise
Mariana ALVES-PEREIRA1 & Nuno Castelo
1Center for Human Performance, Estrada
Nac. No. 10, Edificio Cinema, 2615 Alverca, Portugal; School of Biomedical
Engineering, Sciences and Health Systems, Drexel University, Philadelphia, PA,
19104 USA; and CITIDEP Portugal.
2 Center for Human
Performance, Estrada Nac. No. 10, Edificio Cinema, 2615 Alverca, Portugal.
Background. The importance of information technologies in public
awareness of environmental issues is especially clear when a new occupational
disease is identified. This is certainly the case with Vibroacoustic Disease
(VAD), a whole-body noise-induced pathology, that is not particularly related
to the ear. The Problem. The social and economic costs of VAD are
staggering, and continuously aggravated by the fact that environmental noise
assessments pay little attention to the noise that causes VAD - Low Frequency
(LF) noise (* 500 Hz), focusing primarily on that which causes hearing
impairment. An erroneous assumption justifies these incomplete noise
assessment requirements: noise only affects the ear. Thus, all noise
protection measures and evaluation procedures focus exclusively on the
frequencies affecting the auditory system (* 500 Hz). The Solution.
Physical protection against LF noise is not feasible, given the large
wavelength of LF (in meters). Preventing the evolution of VAD to clinically
severe stages is feasible. The requirements are twofold: a) entry-level
and yearly echocardiogram of job-candidates and exposed individuals; b)
education of workers, occupational physicians, and management. There is an
urgent need to include LF in all noise assessments, and use prevention
medicine against this ubiquitous environmental hazard. However, this can only
be achieved with active participation of a well-informed public.
THE STATUS QUO
Noise pollution is often considered a contained problem because hearing
protection devices are generally efficient, and legislation regarding
noise-induced hearing loss is relatively effective. Additionally, common noise
assessments are a fairly simple process, normally requiring a hand-held
instrument that measures the sound pressure level (SPL) of the acoustic field,
in decibels (dB). Permissible exposure levels are primarily based on the
dB-level measurements, and are regulated on an hourly basis. Noise pollution
is largely regarded as an agent that causes hearing loss and/or minor
annoyance and discomfort. The notion that no other harmful organic effects can
be attributed to noise exposure is widespread, and exceptions to this are few
and far between (Alves-Pereira, 1999).
The human ear captures sound within a specific window of the acoustic
spectrum, generally within the 20-20000 Hz range. However, it is most
responsive to sounds within the mid-frequencies: 1000-10000 Hz. Noise exposure
protection focuses primarily on these frequencies, because its goal is to
prevent hearing loss. Acoustic phenomena within the low frequency (LF) range
(* 500 Hz) are also audible, but require a higher intensity to be perceived.
Infrasound (* 20 Hz) is non-audible to humans; it is therefore considered to
have no impact upon hearing loss, and consequently, environmental noise
assessments within the infrasonic range are a rarity (Alves-Pereira, 1999).
For the remainder of this report, LF noise will refer to acoustic phenomena
within the 0-500 Hz range, hence infrasound is also included.
conservation programs are mandatory in most industrial occupations. Audiograms
and tympanograms are commonly used tests to assess degree of hearing
impairment and existence of noise intolerance. Professional deafness is
normally established when a hearing deficit of 30dB is registered at 4 KHz.
Physical, auricle protection devices (such as earplugs) are also employed to
prevent professional hearing-loss. To adequately characterize an acoustic
environment, both the dB-level and the frequency distribution should be known.
With very few exceptions (Alves-Pereira, 1999), environmental noise
assessments rarely include a frequency spectra analysis. When they are
performed, it is usually for the sole purpose of choosing the best hearing
protection device. Again, this established procedure is based on the
assumption that noise only affects the auditory system. Thus, protection
against noise focuses principally on the hearing function.
whole-body, noise-induced pathology has been an ignored concept. Over the past
decades, scientific investigation into this issue has been infrequent, and
existing data is often regarded as inconclusive (Alves-Pereira, 1999).
Difficulties arise when reports of noise assessments do not include a
frequency spectrum analysis, and only the dB-levels of the acoustic fields are
measured. This has led to an accumulation of parallel studies that cannot be
compared because the descriptions of the acoustic environments are incomplete.
Two environments may have similar dB-levels, but different frequency
distributions. One may have the majority of the acoustic power concentrated in
the mid-frequency bands, while the other may be predominantly within the LF
range (infrasound is not assessed). When studying the effects of noise, it
should be considered insufficient to only provide data on the dB-level of the
acoustic phenomena. The frequency range to which whole-body organ systems
respond is not the same as that for the auditory system. Thus it becomes very
relevant whether the acoustic power is predominantly in the LF range or in the
In modern society, LF noise is ubiquitous; not
only is it found in most industrial environments, but also in nearly all
public transportation, numerous leisure activities, and many urban residential
areas. The extent to which LF noise exposure is responsible for Public health
problems is unknown.
The status quo concepts are that
a. noise only produces an
organic effect on the auditory system;
b. evidence of noise-induced,
extra-aural pathology is inconclusive; and
c. infrasound is non-relevant
for noise-induced pathology.
These concepts can no longer be upheld.
Vibroacoustic disease (VAD) is a noise-induced, whole-body pathology, of a
systemic nature, caused by excessive and unmonitored exposure to LF noise. It
has been identified in aeronautical technicians (GIMOGMA, 1984a ), military
pilots (Carmo et al, 1992 and Canas et al, 1993), commercial
pilots and cabin crewmembers (Alves-Pereira et al, 1999), and
disc-jockeys (Castelo Branco, 1999 and Castelo Branco et al, 1999). VAD
evolves over long-term noise exposure, in years, and can lead to severe
medical conditions, such as cardiac infarcts (Castelo Branco, 1999 and Castelo
Branco et al, 1999), stroke (Castelo Branco, 1999 and Castelo Branco
et al, 1999), cancer (Silva et al, 1996 and Castelo Branco
et al, 1999), epilepsy (Martinho Pimenta et al, 1999a), rage
reactions (Castelo Branco et al, 1999), and suicide (Castelo Branco
et al, 1999). When VAD was first identified in professional groups
known to be exposed to noise, it was initially thought to be limited to the
realm of occupational diseases. However, it has since been diagnosed in
individuals exposed to noise in non-occupational settings, or in seemingly
non-"noisy" environments (Castelo Branco et al, 1999). This rises the
issue of LF noise-induced pathology to the domain ofPublic Health issues.
The evolution of VAD is classified by three stages based on years of
noise-exposure - mild (1-3 yr), moderate (4-9 yr) and severe (10-15 yr).
Please see Table I. This is a departure from current guidelines, which measure
noise-exposure on an hourly basis. The classification of VAD stages was
grounded on a study of 140 aeronautical workers, who had been selected from an
initial group of 306 individuals (Castelo Branco, 1999). Selection criteria
for this study population are given in Table II. LF noise is a stressor, and,
as such, initial exposure causes disorders generally considered as
"stress-related", such as gastrointestinal dysfunction or infections of the
oropharynx. However, LF noise-specific features of VAD can be identified in
the mild stage, such as thickened cardiac structures (Marciniak et al,
1999), increased frequency of sister chromatid exchanges (Silva et al,
1996), immunological changes (Castro et al, 1999), altered values of
hemostasis and coagulation parameters (Crespo et al, 1988), and
specific neurophysiological (Martinho Pimenta et al, 1999a, b and c;
Pimenta et al, 1999) and cognitive (Gomes et al, 1999) changes.
In the severe stages of VAD, as mentioned above, more serious disorders can
There is an important feature that has prevailed among the
many VAD studies performed over the years: a consistent amount of the
noise-exposed workers (usually around 30% of the study population) did not
develop severe stages of VAD (Castelo Branco, 1999). They exhibited milder
symptoms, but never evolved to more critical medical conditions. It is
suspected that survivorship bias may play a significant role. Future studies
of physiological and homeostatic parameters may provide clues as to what
differentiates LF noise-susceptible individuals from the non-susceptible.
VAD is essentially characterized by a proliferation of extra-cellular
matrix. This means that blood vessels can become thicker, thus impeding the
normal blood flow. Within the cardiac structures, the parietal pericardium and
the mitral and aortic valves also become thickened. The most recent VAD
studies have been suggesting that infrasound exposure may be crucial to the
rate of evolution of VAD. Occupational exposure to infrasound is suspected to
cause an increase in the rate of thickening of the pericardium and cardiac
valves in commercial airline pilots over that of flight attendants
(Alves-Pereira et al, 1999).
Among the most serious on-the-job
consequences of untreated VAD are rage-reactions, epilepsy, and suicide. VAD
patients do not have the usual suicidal profile: after the event, if
unsuccessful, they remember nothing, and are confused about the entire episode
(Castelo Branco et al, 1999). Similarly, patients who suffer
rage-reactions also appear confused and seem to remember nothing (Castelo
Branco et al, 1999). These events can have dire consequences if they
occur on the job. Not only can other individuals be injured, but also costly
sophisticated equipment could become irreparably damaged.
The nefarious effects of VAD in the workplace can be successfully
controlled by prevention medicine, and avoided by adequate selection
procedures. This can be preliminarily achieved with a relatively simple
diagnostic method - the echocardiogram. Other diagnostic tests can confirm a
diagnosis of VAD.
Diagnostic Tests for VAD
The echocardiogram is the diagnostic method of choice for a preliminary
diagnosis of VAD (Araujo et al, 1989; Marciniak et al, 1999).
Proliferation of extra-cellular matrix can be observed with various imaging
techniques. The echocardiogram visualizes thickening of cardiac structures,
namely the pericardium and heart valves. In severe cases, echo-Doppler imaging
shows thickened carotid arteries, and transcranial Doppler shows abnormal
cerebral blood flow (Albuquerque et al, 1991). These three diagnostic
tools are non-invasive and are based on principles of ultrasound.
If the echocardiogram shows thickening of cardiac structures then other
diagnostic tests are in order. Brainstem auditory evoked potentials (BAEP)
measure the reaction time of the brain to auditory stimuli. In VAD patients,
these recordings are altered in terms of amplitude and latency values
(GIMOGMA, 1984b; Pimenta et al, 1999). BAEP are also a non-invasive
medical procedure. A thorough neurological examination is useful to
investigate whether other VAD-related signs or symptoms exist, such as balance
disorders (Martinho Pimenta et al, 1999b), palmo-mental reflex
(Martinho Pimenta et al, 1999c) or epilepsy (Martinho Pimenta et
al, 1999a). The existence of brain lesions can be confirmed through
magnetic resonance imaging (Cruz-Maurício et al, 1991 and Pimenta et
A blood test can provide information on the genotoxic (Silva et al,
1996), immune (Castro et al, 1999), and blood coagulation parameters
(Crespo et al, 1988), all of which are altered in VAD patients. Lastly,
CT scan of the lungs can identify lung focal fibrosis which has been seen in
both non-smoker, LF noise-exposed workers (Reis Ferreira et al, 1999),
and in LF noise-exposed animal models (Grande et al, 1999). The
respiratory tract of small rodents, exposed to LF noise on an
occupationally-simulated schedule (8 hours/day, weekends in silence), seems to
be one of the main targets (Sousa Pereira et al, 1999a and b, and
Oliveira et al, 1999), as well as the immune system (Águas et
al, 1999a and b)
The audiogram measures the amount of hearing loss at specific frequencies.
In VAD patients, losses in the lower frequencies are observed (Castelo Branco,
1999). Alone, losses in the LF ranges could be caused by a variety of LF
noise-exposure patterns, for example, excessive use of portable
cassette-players ("walkmans"). The audiogram does not assess whole-body
effects of LF noise exposure, thus it is ineffective as a method to diagnose
Noise is thought to only affect the auditory system. Thus, noise protection
is focused principally on the frequencies of acoustic phenomena that are
audible to humans. Consequently, infrasound is not considered.
Legislation for workers in "noisy" environments are based on hourly
exposures and acoustic amplitude levels. For example, according to the United
States Occupational Safety and Health Administration, a worker can be exposed
to a 90 dB-level acoustic environment for 8 hours per day (OHSA, 1995). No
mention is made to the frequency bands that, together, compose the 90 dB
level. Are they predominantly in the 20-500Hz range, or in the 1000-5000 Hz
range? This is highly relevant information since different organ systems are
susceptible to different acoustic frequencies. Within the 20-500Hz range, 8
hours a day of an acoustic field at a 90 dB amplitude can cause irreversible
damage to several organ systems. However, frequency distribution analyses of
the environment are generally only performed to determine the best hearing
protection device. There seems to be no legislation for infrasound.
If this were a situation with light instead of sound, it would be like
ignoring x-rays (merely a different frequency of visible light), simply
because they can't be seen. Current LF noise protection is analogous to
wearing dark glasses against these x-rays.
The long-term effects of LF noise on living systems is still a wide-open
field of unknowns, and VAD is, as yet, unrecognized by current labor
legislation. The primary reason is the lack of large-scale epidemiological
studies. Past VAD studies have been limited to animal models, and small
samples of 30, 45, 60, and 485 LF noise-exposed workers. The results obtained
urgently warrant that large-scale epidemiological studies be undertaken, and
medical communities, noise-exposed workers, and the public at large be
promptly informed. The extent of LF noise-induced disease in the general
population is unknown. Among noise-exposed workers it continues to be a
Current problems regarding noise-pollution can be
summarized as follows:
a. The steadfast but erroneous concept that noise only causes damage to the
b. Lack of legislation regarding LF noise exposure;
c. A workforce
with increasing absenteeism, lowered productivity, and increased risk in the
d. Widespread effects of LF noise exposure among the general
population are unknown;
e. Public awareness of the danger of LF noise
exposure is close to non-existent.
Recognition of a previously unacknowledged environmental stressor is always
a traumatic event. Classifying LF noise as an agent of disease, and VAD an
occupational pathology, will certainly cause some upheaval, especially since
physical protection against LF noise is not a feasible option. The dimensions
of acoustic barriers are directly related to the wave length of the acoustic
phenomenon. Within the low frequency range, wave lengths can be on the order
of meters. Hence, acoustic barriers would be too large to be practical. At
present, the most successful way to avoid VAD is through methods of prevention
medicine and employee selection procedures.
Among LF noise-exposed workers, VAD can be successfully prevented from
reaching the severe stages if a yearly echocardiogram is administered to the
noise-exposed workforce. Evolution of VAD can thus be followed, and severe
stages of VAD can be avoided. When the effects of VAD-associated pathologies
(See Table I) begin to accumulate, the employee should be removed from the
noise environment and reassigned to a non-"noisy" worksite. Simultaneously,
job applicants for "noisy" jobs should be screened for pre-existing LF noise
exposure and/or VAD. Many popular leisure activities can impose large amounts
of LF noise on the individual, such as rock concerts, dance clubs and
motorized sports. If the echocardiogram reveals some thickening of cardiac
structures, the applicant should be re-evaluated for the position. This is not
discrimination. Selection of individuals to work a particular job has been a
common practice among many professions. For example, aircraft pilots must have
20/20 vision; sky-scraper window-washers and some construction workers cannot
suffer from vertigo; pregnant women do not work with x-rays.
The consequences of the above paragraph are fully recognized. Disruption to
established employer-employee practices will be significant. However, the
undesirable alternative is an increasingly ill society and workforce. The
development of disabilities requiring early retirement, or a change of career,
can shatter the lives of many individuals. For example, to initiate a career
path within a noise-environment job, only to be removed and possibly demoted
within a few years is costly both to a company and to the employee, often
instigating problems within the human resources and management departments,
and with the individual's social and family life. Similarly, if a company
spends time and resources to train individuals for certain noise-environment
positions, the investment return might be null if the individual is only
capable to work for a few years.
Moreover, according to Portuguese labor law, the employer is responsible
for any pre-existing medical condition that is aggravated on-the-job. Since
VAD is not legislated as an occupational disease, and LF noise is not
recognized as an agent of disease, the burden of the medical costs of VAD
patients is currently upon the governmental healthcare system. Furthermore,
workers on sick leave, or who were forced into early retirement due to
VAD-associated disorders are not eligible for any workers' compensation.
Clearly, recognizing VAD as an occupational disease will bring some mayhem,
but ignoring it will have disastrous consequences.
Proposed short-term solutions:
a. All environmental and/or occupational noise assessments should include a
frequency distribution analysis, and evaluation of infrasound levels should be
included in the acoustic evaluation;
b. General physicians should inquire
about the individual's workplace as part of the initial interview;
exposed workers should be made aware of the possible dangers of LF noise
exposure, and should mention to their primary care physicians that they work
in "noisy" environments.
Proposed long-term solutions:
a. Establishment of legislation requiring that all environmental and
occupational noise assessments include a frequency distribution analysis, and
b. Establishment of the echocardiogram as a
mandatory yearly examination of all noise-exposed workers, and as a
pre-requisite for applicants to jobs within "noisy" environments;
Establishment of LF noise as an agent of disease, and VAD as an occupational
disease, so that appropriate compensation can be awarded to the many disabled
THE NEED FOR PUBLIC INFORMATION
All the above information must be made public. It is no longer acceptable
that individuals have their lives destroyed because of excessive LF noise
exposure. Worse than undesirable, it is unethical to keep workers within
"noisy" environments, and ignore the potentially devastating, whole-body,
LF noise environments abound in modern leisure activities; specifically,
rock concerts, dance clubs and powerful car audio equipment, not to mention
the ever so popular water jet skis and motorcycles. Just how widespread are
the LF noise-induced disorders is unknown. The public must be informed
immediately that excessive exposure to these "noisy" activities may limit
their professional future.
An Anecdotal Story
In one of the VAD studies among employees of an aeronautical industry, one
of the subjects initially chosen for the control group worked in the Technical
Drawing Division certainly a quiet environment! As the VAD diagnostic
tests progressed, his came up positive for the LF noise-induced disease. His
mode of transportation to and from work, his current residential area, and his
hobbies were all investigated, and, strangely enough, none suggested exposure
to a LF noise source. Finally, during the last physical examination, in which
he presented all the neurological signs of VAD, the baffled physician
explained the situation to him. With a grin, the man said: "Noise?! I was
exposed to a lot of noise when I was growing up. My parents owned and operated
a water mill, and our house was right above it. I lived there until I was 26
years old." Unfortunately, the mill has since been deactivated, so noise
assessments are no longer possible. Nevertheless, this 34 year old man was
already manifesting signs and symptoms of a moderate stage of VAD (See Table
I) (Castelo Branco et al, 1999). Luckily, he did not decide to become
an airline pilot, an astronaut, a disc-jockey, nor a sound or aircraft
technician or a shipmaster, for example. Had he done so, his condition at 34
years of age may have been much more serious, or even fatal.
Education of the public is crucial. Non-scientific literature on VAD is
also important, and a feeble attempt has been made to fill this void (Paiva
et al, 1998). Management and executive officers must be educated on the
health implications of LF noise exposure on their workers. According to VAD
studies mentioned above, approximately 70% of the population is susceptible to
LF noise. This is all the more alarming since "noisy" environments do not seem
to be having a tendency to decrease much on the
The authors would like to thank all employees who voluntarily contributed
and contribute to the advancement of knowledge on VAD; And also the team of
scientists affiliated with the Center for Human Performance who non-gainfully
collaborate on the
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