Nagoya International Symposium on Human Responses to Hand-Arm Vibration. November 5-7, 1993
Research into Hand-Arm Vibration Syndrome and its Prevention in Japan
SHIN'YA YAMADA and HISATAKA SAKAKIBARA
pg(s) 3- 17
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Research on vibration syndrome in Japan began in the 1930s with studies of the disorder among railway, mining and shipyard workers. In 1947, the Ministry of Labor decided vibration syndrome among operators of rock drills and riveters etc. was an occupational disease. Industrial developments in the 1950s and 1960s promoted the survey of vibration syndrome in mining, stone quarrying and forestry. The Ministry of Labor (1965) and the National Personnel Agency (1966) legally recognized vibration syndrome among chain saw operators as an occupational disease. Guidelines for prevention and early therapy were issued in the 1970s and 80s. From the late 1970s into the 1980s, research focused on the clinical picture, diagnostic methods and therapy. In pathophysiology, advances were made in research into the autonomic nervous system during the 1980s. The 1970s and 80s saw a steady reduction in risk from technological change and working conditions, and advances in medical care, education and meteorological forecasting. A comprehensive prevention system established in the 1980s in the Japanese forest industry involved: 1) work restrictions, 2) an improved health care system, 3) advances in the design of vibrating tools, handle-warming devices, and 4) improved worker education. This comprehensive preventive system was legally introduced into other industries, resulting in a rapid decrease in the incidence of vibration syndrome in Japan.
Pathophysiology and Clinical Picture of Hand-Arm Vibration Syndrome in Japanese Workers
TSUNETAKA MATOBA
pg(s) 19- 26
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Hand-arm vibration syndrome is an occupational disease induced by long-term use of vibratory tools such as rock drills and chain saws. The three major stressors of vibration, noise and cold may produce various symptoms and signs not only with peripheral circulatory, nervous and muscle-joint disorders but also with general disorders. It is a point of controversy whether the symptoms and signs should be limited in the peripheral disorders. The question may involve differences in definition: vibration alone or work mode with vibratory tools. There are two viewpoints in the staging: peripheral and general viewpoints. The key concept in the peripheral viewpoint staging is a checkup to find disorders at the early stage and classify the peripheral disorders of the digits in detail. The general viewpoint staging seeks to grasp the general pictures of patients, and to classify from light to severe cases in the treatment. Clinical manifestations may include the general disorders in proportion to the severity of the syndrome according to our clinical experience. A differential diagnosis should be carefully made in the light of legal, medical and economic compensation. The treatments that we have used for approximately 20 years have beneficial effects on the whole-body, which include 1) physiobalneotherapy (therapeutic exercise, exercise in a pool and physiotherapy), 2) drug therapy (vasodilating drugs, autonomic stabilizers, etc.), 3) nerve blocking therapy, 4) surgical therapy for ulnar nerve paralysis or paresis, and 5) education for patients. Even with these therapies, a beneficial effect may not be observed in a short period. The recovery may be slow.(ABSTRACT TRUNCATED AT 250 WORDS)
Clinical Assessment of Hand-Arm Vibration Syndrome
PETER L. PELMEAR and ROBERT KUSIAK
pg(s) 27- 41
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The clinical assessment of patients thought to be suffering from hand-arm vibration syndrome (HAVS) requires the use of multiple vascular and sensory tests. In a family physician's office, Adson's, Allen's and cold water immersion of the hands are the only feasible vascular tests, while the sensory tests have to be limited to assessing impairment of skin sensitivity and manipulative dexterity. This paper reviews the laboratory tests deemed to be useful in a hospital or clinic facility, and reports on the investigation of 364 patients exposed to hand-arm vibration who were examined in Toronto, Canada during the period 1989-92. A statistical clustering algorithm was used to categorise 138 male subjects according to the results of their diagnostic tests. From the cluster analysis, four vascular and four sensorineural categories of impairment were recognised in patients suffering from HAVS. The Stockholm vascular classification stages and the four vascular clusters were found to correspond. The Stockholm sensorineural classification (Stages 1, 2, and 3) correlated with clusters formed from the sensory tests evaluating the sensitivity of the nerve endings and the distal digital branches of the median and ulnar nerves. When the myelinated nerve fibres were affected, as detected by abnormal Tinel's, Phalen's, and nerve conduction tests, an additional cluster group emerged. The subjects with abnormal nerve conduction test results constituted a distinct group with increased impairment, so there is a need for them to be categorised separately i.e. as a Stage 4. It is suggested that a Stage 4 be included in the Stockholm sensorineural classification.
Hand-Arm Vibration Exposure and the Development of Vibration Syndrome
KAZUHISA MIYASHITA, KUNIHIKO MIYAMOTO, MOTOTSUGU KURODA, SHINTARO TAKEDA and HIROTOSHI IWATA
pg(s) 43- 48
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To evaluate the circulatory disturbances, sensory disturbances and damage to muscles and joints by chain saw vibration exposure, the process of the deterioration of the symptoms with chain saw operating time was studied. Subjects were classified into eight groups according to TOT (Total Operating Time): Group 0, 46 controls; Group A, 39 operators (< 2,000 hours); Group B, 53 operators (2,000-4,000 hours); Group C, 45 operators (4,000-6,000 hours); Group D, 29 operators (6,000-8,000 hours); Group E, 31 operators (8,000-10,000 hours); Group F, 35 operators (10,000-15,000 hours); and Group G, 34 operators (> 15,000 hours). The subjective symptoms and clinical findings due to operating chain saws were divided into three main categories of peripheral circulatory disturbances, sensory disturbances and damage to muscles and joints. According to the criteria, the total score of each disturbance was calculated per individual in Group 0 and Groups A through G, respectively. The scores for the three (circulatory, sensory, muscles and joints) disturbances increased significantly with the increase of TOT. The scores for circulatory disturbances increased significantly in Group A and B, as compared with those in its previous Group, respectively. The scores for sensory disturbances increased significantly in Groups A, B, and F. The scores for damage to muscles and joints increased significantly in Group B.
Correlations among Examination Findings, Subjective Symptoms and Classification of Stages in Vibration Syndrome
SHIN'YA YAMADA, HISATAKA SAKAKIBARA, MAKOTO FUTATSUKA, NORIAKI HARADA and MINORU NAKAMOTO
pg(s) 49- 57
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From data collected in 1966, 1973, 1986 and 1989, we analyzed the correlations among examination findings, subjective symptoms, stages in the disorder of vibration syndrome and vibration exposure. As vibration syndrome progressed and vibration exposure accumulated, abnormality of examination findings, the prevalence of vibration induced white finger (VWF), numbness (N) and other subjective symptoms increased. Abnormality of examination findings and prevalence of subjective symptoms in the VWF(+) N(+) group were greatly different from those in the VWF(-) N(-) group. Both findings and symptoms showed closer correlations with VWF(+) than with N(+). Stages in the disorder traced the progression from VWF(-)N(-) to VWF(-)N(+), then to VWF(+)N(+/-), and finally to VWF(+/++)N(+/++). Pathophysiologically, it seems that VWF(+) and N(+) relayed many more cold and pain signals from the hand to the central nervous system. Such signals may activate autonomic nervous activity. In the recovery, subjective symptoms correlated more closely with N(+) than with VWF(+). This is because VWF involves the autonomic nervous system's hyperactivity and hypersensitivity to cold, both of which subside gradually in the recovery; N, however, involves pathological changes in nerve tissue which are irreversible.
Autonomic Responses to Environmental Stimuli in Human Body
TADAAKI MANO
pg(s) 59- 75
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The author reviewed in this paper current microneurographic findings on the responses of muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA) to the environment in humans with special reference to vibration-induced white finger (VWF). 1) MSNA was enhanced by +Gz gravitational input, while being suppressed by simulated weightlessness through the baroreflex mechanism to maintain hemodynamic homeostasis. 2) MSNA was enhanced by hypobaric hypoxia through the chemoreflex mechanism. 3) SSNA was lowest under thermoneutral ambient temperature condition. Sudomotor component of SSNA increased under hot ambient temperature, while vasomotor component of SSNA increased under cold ambient temperature. 4) MSNA and vasomotor component of SSNA increased by local cold stimuli such as when a hand was immersed into cold water. 5) SSNA was enhanced by local vibration of the human body. The vibratory frequency of 60 Hz was the most effective for vibration-induced SSNA response. With a constant vibratory frequency of 60 Hz, SSNA increased depending on the vibratory acceleration. MSNA was not enhanced by local vibration of the body. 6) SSNA was markedly enhanced by combined stimuli of local vibration and noise. 7) MSNA increased during handgrip exercise, presumably depending on afferent inputs from muscle metaboreceptors. 8) The sympathetic response to environmental stress was markedly influenced by aging. The basal level of MSNA increased with aging, while the MSNA responsiveness to gravitational stress became reduced by aging. MSNA responsiveness to simulated weightlessness was also reduced by aging. 9) Vibration-induced white finger may be related to complex autonomic dysfunctions including excessive somato-sympathetic reflex induced by local vibration, cold stimuli and handgrip exercise. Gravity-dependent sympathetic nerve responses and the influence of aging may also contribute to the underlying mechanisms of VWF.
Autonomic Nervous Function of Hand-Arm Vibration Syndrome Patients
NORIAKI HARADA
pg(s) 77- 85
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We have investigated the autonomic nervous function of hand-arm vibration syndrome patients using blood chemical analyses and electrophysiological methods. When exposed to whole body cooling, hand-arm vibration syndrome patients showed a significantly greater increase of plasma norepinephrine than the age-matched healthy controls. The patients also exhibited reduced variation of R-R intervals in electrocardiogram during deep breathing. When classifying the subjects according to the Stockholm Workshop scale of VWF, the subjects of stage 3 showed the most remarkable findings followed by the subjects of stage 2. The findings of the stage 3 subjects were also greater than those of diabetes patients. The excess secretion of norepinephrine in blood reveals that the responsiveness of the sympathetic nervous system to cold exposure is enhanced in hand-arm vibration syndrome patients. The R-R interval variation suggests that the basal activity of the parasympathetic nervous system is reduced. We observed that plasma norepinephrine also increased during short-term exposure of hand-arm to vibration and noise exposure potentiated the effect. It seems likely that repeated vibration exposures of the hand-arm system develop the hyperactivity of the sympathetic nervous system.
Pathophysiology of White Fingers in Workers Using Hand-held Vibrating Tools
GÖSTA GEMNE
pg(s) 87- 97
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The pathogenic events and the localization of the primary lesion in white fingers among persons using hand-held vibrating tools are still unclarified. A "vibration disease" has been proposed to be due to damage to the limbic system and other brain structures which causes autonomic dysfunction. Current common opinion regards the pathogenesis of white fingers to be a result of longterm exposure to various physical and psychological environmental stressors, but the relative importance of one stressor or other is unknown. Observations indicating a chronic autonomic disturbance include changes in cardiac functions, excessive hearing loss in persons with VWF, and reduced toe skin temperature also in the absence of acute cold or vibration exposure. Sympathetic hyperactivity alone has long been postulated to account for vibration-induced white fingers, but damage to vaso-regulatory structures and functions in the finger skin now also seems to be involved. An abnormal level of sympathetic efferents is likely to be important for producing the symptoms in white fingers. Recent findings, however, indicate that the pathogenesis also involves changes in alpha-adrenergic receptor mechanisms as well as endothelial damage with deficient function of endothelial-derived relaxing factor. The role of vessel lumen reduction due to organic changes and an increase in whole blood viscosity remains unclarified. The understanding of the influence of confounders such as cold exposure, smoking habits and variations in individual susceptibility is also lacking. In particular, the physiological complexity of the response to cold is so great and the interaction between various vaso-regulatory mechanisms so intricate that only a multifactorial etiology and pathogenesis is likely for Raynaud's phenomenon in persons using hand-held vibrating tools. A model is suggested for the manifestation of abnormally strong vasoconstriction and white fingers as a result of a narrowing of the gap between the individual symptom threshold and the level of sympathetic activity.
Sympathetic Responses to Hand-Arm Vibration and Symptoms of the Foot
HISATAKA SAKAKIBARA
pg(s) 99-111
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Vibration syndrome is generally considered to consist of disorders in the upper extremities which are directly exposed to vibration. However, it has been shown that vibration syndrome patients have circulatory disturbances in the foot as well: several chain-saw operators, who were little exposed to vibration of the foot, had Raynaud's phenomenon of the toes, and those with frequent attacks of vibration-induced white finger (VWF) had a higher prevalence of coldness felt in both the hands and the feet, and the patients with VWF had lower skin temperature of the toes as well as the fingers. Moreover, arterial pathological changes like medial muscular hypertrophy have been observed in both the fingers and the toes of the patients. Hand-arm vibration elicits a sympathetic nervous reflex, leading to vasoconstriction of the four extremities. Long-term repeated vasoconstriction may result in such arterial changes and then circulatory disturbances of the feet.
Effect of Hand-Arm Vibration on Inner Ear and Cardiac Functions in Man
ILMARI PYYKKÖ, MARKUS FÄRKKILÄ, RYOICHI INABA, JUKKA STARCK and JUSSI PEKKARINEN
pg(s)113-119
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To evaluate distant effects of hand-arm vibration we studied Finnish forestry workers using chain saw during the years 1972 through 1990. The hearing was tested annually and individual regression curves for sensorineural hearing loss (SHL) were calculated. Robinson's model was used in prediction of SHL. The heart rate variation (HRV) indexes at rest and during deep breathing test were analyzed to measure autonomic nervous function. In Robinson's model the measured SHL (17.8 dB) respected the predicted SHL (17.2 dB). The subjects with VWF had on average, 10 dB greater hearing loss than those who did not have VWF. The regression model based increase of hearing loss during follow up correlated with ageing, not to VWF. The intercept differed significantly in those with VWF from those without VWF. We found a significant difference between HRV indexes during deep breathing test in those with the shortest and those with the longest vibration exposure. The HRV decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with HRV indexes. Our results suggest that prolonged exposure to vibration caused by chain saw has negative effects an autonomic functions. The aggravated hearing loss in subjects with VWF may be due to vibration induced changes in the autonomic nervous system or internal factors of the blood vessels.
Raynaud's Phenomenon of Fingers and Toes among Vibration-exposed Patients
NORIKUNI TOIBANA, NOBUHIDE ISHIKAWA, HISATAKA SAKAKIBARA and SHIN'YA YAMADA
pg(s)121-128
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Eleven patients with Raynaud's phenomenon of the toes as well as the fingers were encountered among about 1,000 vibration-exposed patients. They consisted composed of four chain-saw operators, five rock drillers, a stone quarrier and a welder in a shipyard. All the cases were examined carefully for differential diagnosis, but there were no particular abnormalities in hematological, immunological and homodynamic examinations. The rock drillers, quarrier and welder had direct vibration exposure of the foot, which was considered to be responsible for their Raynaud's phenomenon of the toe. Four chain-saw operators, who had been little exposed to vibration of the foot directly, were examined further on skin temperature of fingers and toes every three hours except at night and in a 30-min cold provocation test at 5 degrees C. The skin temperature of both their fingers and toes was lower than in age-matched healthy controls. The chain-saw operators started to work in the 1960's and early in the 1970's, when the chain saw vibration level was high. It is, hence, considered that they were exposed to strong vibration of the hand from chain saws, and then suffered severe Raynaud's phenomenon of both fingers and toes.
Pathological Changes of Finger and Toe in Patients with Vibration Syndrome
TOSHINORI HASHIGUCHI, HIDETAKA YANAGI, YOSHITAKA KINUGAWA,
HISATAKA SAKAKIBARA and SHIN'YA YAMADA
pg(s)129-136
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Pathological findings of the fingers and toes were studied in finger and toe skin specimens from 21 male patients with vibration syndrome and 13 referent male cadavers. Thickening of the medial muscle layer of small arteries or arterioles, and increase of collagen fibers in the connective tissues, especially in perivascular regions, were noted in not only the finger but also the toe in patients with vibration syndrome. The ratio of the media/external diameter in the finger and toe was significantly greater in the patients than in the referents, even in the patients who had operated chain saws, bush cutters or grinders and had not been exposed to vibration of the foot directly. And the ratio in the finger was approximately parallel with that in the toe in the same subject. The present findings pathohistologically confirmed the existence of circulatory disturbances in the feet as well as the hands. The medial thickening of arteries and perivascular fibrosis in the toe can result from not only direct vibration exposure of the foot, but also long-term repeated vasoconstriction and circulatory disturbances in the foot through the activation of the sympathetic nerve system caused by hand-arm vibration.
Vibration-induced White Finger as a Risk Factor for Hearing Loss and Postural Instability
MASAYUKI IKI
pg(s)137-145
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Effect of vibration-induced white finger (VWF) on the hearing was examined in 289 Japanese forest workers. From 51 subjects suffering from VWF and 228 with no history of VWF, 37 pairs were formed, matched for age and hours of noise exposure. The cases with VWF had a significantly higher hearing threshold at 4 and 8 kHz than their matched controls. This result was corroborated by the follow-up study which showed significant deterioration of hearing at 2 and 4 kHz only in subjects with VWF during five-year follow-up period. The possible effects of VWF on the postural stability were investigated in 71 Finnish forest workers. Postural stability was evaluated by an average velocity of the body-sway (ASV) measured with a force platform technique. Neither age nor exposure duration to chain saw noise and vibration correlated with ASV. A significant positive correlation was found between ASV and hearing level at 4 kHz after allowing for the effects of the exposure. Multiple regression analysis of ASV on age, exposure hours, hearing level at 4 kHz and prevalence of VWF showed that the hearing level and VWF had significant and almost significant effects on ASV, respectively. Thus, the workers suffering from VWF developed greater hearing loss and the hearing loss correlated with ASV. VWF explained some variance of ASV in the regression analysis. VWF seemed to play some role in hearing deterioration and possibly in genesis of balance disorder.
Foundations of Hand-transmitted Vibration Standards
MICHAEL J. GRIFFIN
pg(s)147-164
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Standards for hand-transmitted vibration predict dependent variables (e.g. finger blanching) from measurements of a few independent variables (e.g. vibration magnitude, vibration frequency, exposure duration). This paper illustrates the assumptions in the current International Standard guidelines for the evaluation of hand-transmitted vibration and compares research methods which may provide information to improve the guidance. Subjective assessments of vibration discomfort have influenced the frequency weighting used in current standards, but the data have been modified greatly for this purpose. Subjective and biodynamic data suggest that the severity of vibration may not be similar for vibration occurring in different axes. Physiological and pathological studies seek to uncover the mechanisms involved in the temporary and permanent changes caused by vibration, but they have yet to contribute to the guidance in standards. Future experimental studies in humans are unlikely to be sufficient to determine how injury depends on the characteristics of vibration exposures at work. Epidemiological studies are required to uncover the effects of occupational exposures, but the complexity of occupational exposures will prevent the formulation of standards based solely on the results of epidemiological studies. Standards for hand-transmitted vibration include unproven assumptions but, for those assessing the severity of occupational exposures, they offer the most reasonable method for predicting the likely effects of vibration. A combination of subjective, biodynamic, physiological, pathological and epidemiological studies is required to improve current guidance.
Impulsive Vibration and Exposure Limit
LADISLAV LOUDA, DARINA HARTLOVÁ, VLADIMIL MUFF, LIBUŠE SMOLÍKOVÁ and LADISLAV SVOBODA
pg(s)165-172
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Several cases of exposure to hand-transmitted shocks in two different factories were studied with an intention to improve our knowledge about the influence of the impulsive components of vibration on human being. Two types of shocks affecting the workers could be distinguished, i.e., shocks having small amount of energy at frequencies higher than 100 Hz and shocks having relatively high frequency components up to 1000 Hz. An exposure to the hand-arm shocks of both types was measured and assessed in accordance with the international standard ISO 5349. Health condition of workers was examined. Carpal tunnel syndrome was found among the workers of the workshop in wood industry, who work with staple gun. The investigation of the health condition of about 60 forge workers up to now did not confirm the severity of hand-arm shocks as it had been assessed according to the Annex A of the ISO 5349. The exposure to hand-arm shocks in the forge leads to the incidence of occupational diseases and disorders, which however, differ from the diseases normally reported as a consequence of the hand-arm vibration and shocks. It seems obvious that for the assessment of shock exposure, the ISO 5349 is not quite suitable in its present form.
Operating Hand-held Vibrating Tools and Prevalence of White Fingers
S. MOHAMMAD MIRBOD, RYOICHI INABA and HIROTOSHI IWATA
pg(s)173-183
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Hand-transmitted vibration levels (HTVLs) and the prevalence of vibration-induced white finger (VWF) and numbness of the hands were investigated in eight groups of subjects operating various hand-held vibrating tools. The prevalence rates of Raynaud's phenomenon (RP) and numbness of the hands in 1,027 males and 1,301 females not occupationally exposed to vibration were compared to those of the exposed subjects. The prevalence of VWF was in the range of 0.0-4.8% in subjects exposed to HTLVs of between 1.1 to 2.5 m/s2 and reached 9.6% in a group of workers exposed to HTLVs of 2.7-5.1 m/s2. The latter group showed a significant difference (P < 0.05) in the prevalence of VWF compared to the 2.7% prevalence of RP in male subjects of the general population. The prevalence of VWF in female subjects exposed to vibration (4.3%) was not significant compared to the prevalence of RP in females of the general population (3.4%). The prevalence rates of numbness of the hands were between 6.5% and 30.4% in the exposed groups and in the range of 13.4-29.5% in the general population. It was concluded that in decisions concerning quantitative recommendations for vibration exposure, the prevalence of VWF should be employed. To decrease the risk of developing VWF, estimated vibration safety values for 4 h and 2 h daily exposures are discussed.
Temporary Threshold Shifts in Fingertip Vibratory Sensation from Hand-transmitted Vibration and Repetitive Shock
SETSUO MAEDA
pg(s)185-193
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Temporary threshold shifts (TSSs) in vibrotactile perception produced by continuous vibration and repetitive shocks having one complete cycle of a 100 Hz sine wave and exponential decays. The repetition rate of the cycles was 5, 25, 50, or 100/s, while the root-mean-square (r.m.s.) acceleration measured over exposure of five minutes was held constant (weighted according to British Standard (BS) 6842 and International Standard (ISO) 5349). When exposed to five shocks per second at each of the three frequency-weighted acceleration magnitudes, the subjects developed a small TTS. Exposure to 100 shocks per second (continuous vibration) at each of the three frequency-weighted acceleration magnitudes caused a large TTS, although the total frequency-weighted energy was the same as when exposed to five shocks per second. The results suggest that the equal energy hypothesis underlying BS 6842 and ISO 5349 is inappropriate for the prediction of the TTS produced by repetitive shocks.
Vibration Exposure and Prevention in Japan
MAKOTO FUTATSUKA, TATSURO UENO and SHIN'YA YAMADA
pg(s)195-202
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Working conditions of vibration exposure have generally improved, but many difficult problems must be solved such as (1) hygienic improvements in a variety of vibrating tools; (2) improving working conditions, for example, by limiting the time of operation in spite of economic difficulties such as those faced by those who work on a piece rate basis; (3) gathering more complete information about the risk population because of the large number of self-employed in informal employment sectors; and (4) finding work places after rehabilitation for patients, particularly in mountainous rural areas or in small scale industries. Historical observation of vibration and preventive measures in Japanese national forests was presented on the basis of the results of a retrospective cohort study in Kyushu, Japan. Prevalence rate of VWF remarkably changed from 58.4% in the groups that began to operate chain saws in 1960 to only a few cases in the groups who started the operation after 1971. When we compare the relationships between the results of long term cohort study and the consequences of preventive measures of vibration syndrome, the most important factor is the decrease of vibration exposure (improvement in chain saws plus the time restriction system). The comprehensive prevention system used in Japanese national forests consists of the following: (1) Health care system; (2) Work regulation system; (3) System for improving mechanized tools; (4) Warming system to protect against cold conditions; and (5) Education and training system.
Vibration Exposure and Prevention in Finland
JUKKA STARCK, ILMARI PYYKKÖ, KAIJA KOSKIMIES and JUSSI PEKKÁRINEN
pg(s)203-210
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The number of annually compensated occupational diseases due to exposure to hand-arm vibration (HAV) has decreased during the last 15 years. The number of exposed workers has been declining in Finland, especially in forestry work, as harvesters have increasingly replaced manual chain saw operations. During the entire 1970s, forest work caused more cases of vibration-induced occupational diseases than all industrial branches together. The decrease is mainly due to the technical development of chain saws, but also to the effective health care services in Finland. Other factors such as warm transport, warm rest cabins in which to take pauses at work, warm meals, adequate protective clothing, and vocationally adjusted early medical rehabilitation have helped to cut down health hazards, especially in forest work. The number of new cases has been decreasing in Finland not only in forestry but also in other industries. In Finland a considerable amount of research has been conducted to hand-arm vibration, resulting in the increased awareness of the health risks related to certain occupations. This has helped to carry out the Primary Health Care Act (1972) followed by the Occupational Health Care Act (1979) which obligates employers to arrange occupational health care for their employees. We believe that the research activity has contributed significantly to achieving the present health in Finnish work places. The purpose of the present paper is to describe the cases of occupational exposure to HAV, and the effectiveness of different preventive measures in Finland.
Vibration Exposure and Prevention in the United States
DONALD E. WASSERMAN
pg(s)211-218
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There are over one million workers exposed to hand-arm vibration in the United States. Cases of hand-arm vibration syndrome have been reported in the U.S. since 1918. Typical hand-arm vibration exposure conditions are given in this presentation. Vibration control methods are discussed; these include vibration damping and isolation, use of antivibration (A/V) tool and gloves, and the application work practices and hand-arm vibration standards in the workplace.
Technical Preventive Measures in Japan
YOSHIHARU YONEKAWA
pg(s)219-228
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Technical preventive measures against vibration syndrome in the field of industrial health are reviewed in the present paper. The first technical prevention measure is to reduce vibration transmission from the tools to the operators. This measure employs vibration isolators between the handles and vibration sources of machine tools. Handles of tools using Neidhalt dampers, shear type rubber mounts and springs have reduced frequency-weighted acceleration levels (Lh,w) from 2 dB to 10 dB (Lh,w (dB) = 20 log a/ao; a: frequency-weighted acceleration (rms), ao = 10(-5) m/s2) in Z direction, while no reduction was found in X, Y directions. The second measure is to reduce vibration at the source; New chain saws have been developed to reduce vibration with twin cylinder instead of a single cylinder engines. This cancels unbalanced movements inside the internal combustion engine. Such chain saws reduced Lh,w values more than 10 dB in both front and rear handles except in Z direction of the front handle. A new type of impact wrench has been devised with an oil pulse device to avoid direct metal contact inside the power source. This new impact wrench lowered Lh,w values more than 10 dB in three directions. The third measure is to use a remote control system or to substitute another machine generating less vibration. Vibration reduction at the handle lever of the remote control chain saw was more than 20 dB. A more effective means is to substitute other machines for conventional tools: a hydraulic wheel jumbo instead of a leg-type rock drill; a hydraulic breaker instead of a hand-held breaker. However, these heavy machines produce whole-body vibration which might give rise to other problems such as back pain.
Improvement of Chain Saw and Changes of Symptoms in the Operators
HIDEYOSHI SUZUKI
pg(s)229-234
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The average maximum acceleration levels of chain saws by the one-third octave band analyzer decreased considerably from 5.1 G (range: 2.5 to 8.0 G) during 1965-1975 to 1.7 G (range: 1.0 to 2.5 G) during 1976-1988. The effects of this reduced vibration level on the prevalence of vibration syndrome were studied by comparing two groups of male chain-saw workers: 285 who started to use chain saws before 1976 and were examined in 1975-1976; and 230 who started chain-saw work after 1976 and were examined during 1985 to 1988. As compared with the pre-1976 group, the prevalence of white fingers among the post-1976 group was one-seventh in chain-saw use of less than 5 years, about one-eighth in that from 5-9 years, and less than one-tenth in that of 10 or more years. Complaints of numbness or coldness in fingers or hands, and pain in hands or arms also decreased considerably from about one-fourth to less than one-tenth. This considerable reduction in the prevalence of vibration syndrome is attributable, above all, to a marked reduction in the acceleration levels of chain saws since about 1976, and secondarily to decreased total hours-per-year of vibration exposure due to improvements in general working conditions
Vibration Exposure and Symptoms in Postal Carriers Using Motorbikes
YOSHIO TOMINAGA
pg(s)235-239
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An investigation was made on vibration exposure among postal carriers using motorbikes (mainly letter carriers) and vibration symptom manifestations as a means to obtain information on hand-arm vibration exposure limits. The first report deals with the correlation of vibration and cold exposure with white finger symptoms. The group in which daily vibration exposure was greatest, for which the 4-hour equivalent value of the frequency weighted vibration acceleration was estimated to be above 2 m/s2, showed a greater incidence of white finger than other groups, and the changes synchronized with the timing of motorbike antivibration measures. This group, however, also displayed evidence of varying degrees of cold-exposure white finger. The vibration exposure limit was considered to be over 2 m/s2 as the 4-hour equivalent value of the frequency weighted vibration acceleration.
