Diagnostics of hand-arm system disorders in workers who use vibrating tools.

A hand-arm vibration syndrome occurs in some workers who use hand held vibrating tools. It is recognised to consist of white fingers, diffusely distributed finger neuropathy, pain in the arm and hand, and a small excess risk of osteoarthrosis from percussion to the wrist and elbow. Carpal tunnel syndrome is mainly due to ergonomic factors other than vibration, but certain factors related to vibration may contribute to its development. A decrease in muscle power induced by vibration, and excessive hearing deficit have been postulated. The assessment of a disorder suspected of being induced by vibration includes deciding whether there is a disorder and, if so, whether the symptoms can be caused by vibration. To decide whether the symptoms can be caused by vibration epidemiological documentation and pathogenically reasonable theories must exist. A causal diagnosis finally requires and epidemiological decision whether or not the factual exposure has elicited the patient's symptoms. Epidemiological data on the quantitative association between vibration and excessive risks of white fingers and diffusely distributed neuropathy are incomplete. The symptomatic diagnosis of white fingers is still mainly based on anamnestic information. Available laboratory tests are incapable of grading the severity of individual cases. Recording the finger systolic blood pressure during cold provocation is a method of symptomatic diagnosis with reasonable levels of specificity, sensitivity, and predictive value. For diffusely distributed neuropathy these levels are lower than desired. Electrodiagnostic tests for carpal tunnel syndrome have sufficient validity. Proper exposure evaluation must be based on an appreciation of the character of the vibration as well as effective duration and intermittency. If this is not taken into account, the number of hours of exposure and intensity of vibration are likely to be non-commensurable variables, and the simple product of them is a questionable dose measure. Separate models for risk evaluation of vascular and neurological disorders related to work with different tools and processes will have to be established. Ongoing research to obtain further data on exposure-response relations for neurological disturbances begins to yield encouraging results.

Evaluation of the white finger risk prediction model in ISO 5349 suggests need for prospective studies.

The risk prediction model for white fingers in Annex A of ISO 5349 is not likely to offer protection from all tools and all work processes. It is also probable that some work place changes it has initiated are either redundant or lack the intended effect. The main reasons for these shortcomings are the following. The often demonstrated disagreement between predicted and observed white fingers occurrence may be related to the fact that the model is based on latency data. This leads to an overestimation, to an unknown extent, of true group risks. A possible healthy worker effect, resulting in underestimation, has not been considered, and uncertainty because of recall bias is connected with using latency as effect variable in a slowly developing disorder like white fingers. The diagnostic criteria for white fingers have varied over the years, causing a possible inclusion of circulatory disturbances other than those induced by vibration. Among insufficiently clarified matters unrelated to vibration are variations in individual susceptibility and other host factors that modify vibration effects, uncertainty concerning daily or total effective exposure, and the fact that variation in work methods and processes as well as ergonomic factors other than vibration tend to make different groups incomparable form the viewpoint of risk of injury. Lack of sufficient data on vibration measurements and employment durations add to the uncertainty, as do variations in tool conditions (grinder wheels, etc) and inherent difficulties in measurement. Finally, the ISO 5349 frequency-weighting curve only relates to acute sensory effects rather than chronic effects on vascular functions like white fingers, and directional difference in sensitivity has not been incorporated in the curve. Data on exposure-response relationships are needed from prospective studies that monitor the dose of exposure to special vibration types and all relevant environmental agents, employ diagnostics with good sensitivity, specificity and predictive value, and pay attention to environmental or individual confounding factors and effect modifiers. Before such data are available, the ISO 5349 model should not be used for risk prediction. It can serve, however, as an incentive for manufacturers to produce tools that vibrate less, and for employers to implement practical measures in order to reduce the total and dose of effective exposure.

Acute effects of vibration from a chipping hammer and a grinder on the hand-arm system.

OBJECTIVES: The purpose of this study was to compare various effects on the hand-arm system of vibration exposure from a chipping hammer and a grinder with the same frequency weighted acceleration. Grip and push forces were measured and monitored during the exposure. The various effects were: muscle activity (measured with surface electrodes), discomfort ratings for different parts of the hand-arm system (made during and after exposure), and vibration perception threshold (for 10 minutes before and 10 minutes after the exposure). RESULTS: No increase in muscle activity due to exposure to vibration was found in the hand muscle studied. In the forearm, conversely, there was an increase in both muscle studied. For the upper arm the muscle activity only increased when exposed to impact vibration. Subjective ratings in the hand and shift in vibration perception threshold were effected more by the grinder than the hammer exposure. CONCLUSION: These results show that the reaction of the hand-arm system to vibration varies with frequency quantitatively as well as qualitatively. They do not support the notion that one single frequency weighted curve would be valid for the different health effects of hand-arm vibration (vascular, musculoskeletal, neurological, and psychophysiological).

Pathophysiology of white fingers in workers using hand-held vibrating tools.

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.

Where is the research frontier for hand-arm vibration?

A central question for current hand-arm vibration research is how to combine diagnostics with exposure evaluation so that reliable risk assessments can be made for different tools and work processes. The scientific foundation of the model, in annex of A of ISO 5349, for white finger (WF) risk prediction has been shown to be insufficient. Prospective epidemiologic studies are needed to establish exposure-response relationships addressing the specific etiologic factors. Another important research field concerns WF pathogenesis, which is likely to be a vessel wall lesion causing vasodilatory deficiency. Epidemiologic research, in combination with human and animal experimentation, on endothelium-dependent mechanisms is desirable, among other things, because a therapy may be within reach. A model is presented for the manifestation of cold-triggered WF in persons with exposure to vibration and other environmental stressors as a result of lowered symptom threshold and a raised level of sympathetic activity.

Correspondence between neurological symptoms and outcome of quantitative sensory testing in the hand-arm vibration syndrome.

To evaluate neurological symptoms in the vibration syndrome, 55 patients with vascular and neurological symptoms in the hand who had been exposed to vibration were examined. Their exposure to vibration was estimated and neurological vascular symptoms were evaluated according to symptom scales. Temperature thresholds were measured on the right thenar eminence and on the distal volar aspect of the second and third fingers held together on both sides. Vibration thresholds were measured dorsally on the second and fifth metacarpal bones and on the second and fifth fingers proximal to the nail roots. Subjects with advanced neurological symptoms had higher temperature and vibration thresholds than subjects with less advanced symptoms. No such relation was found between vascular symptoms and the outcome of sensory testing. Thus neurological but not vascular symptoms are reflected by the outcome of quantitative sensory testing. In subjects with advanced neurological symptoms the tests gave a high proportion of abnormal results, indicating that these tests may be used for the diagnosis of vibration syndrome on an individual basis. Patients with advanced vascular and neurological symptoms had higher exposure dose scores than patients with less advanced symptoms, indicating a dose response relation between vibration "dose" and neurological and vascular symptoms.

Malignant melanoma in the printing industry.

To evaluate a recent report of malignant melanoma among printers, we used the Cancer-Environment Registry of Sweden, which links national cancer incidence and employment data. Employees in the newspaper printing industry had almost twice the incidence of melanoma than expected (p less than 0.01). Elevated risks were found not only among typographers and machine repairers, but also among journalists, editors, and business executives in the printing industry. Further studies are needed to clarify this relationship and identify specific exposures that may be responsible.

Bone and joint pathology in workers using hand-held vibrating tools. An overview.

A literature evaluation was made with regard to the radiological documentation of bone and joint pathology in the hands and arms of workers using vibrating tools. There is evidence that work with pneumatic percussive tools (such as chipping hammers and scalers) may cause premature elbow and wrist osteoarthrosis, although of very low prevalence. This work-related disorder is not specific to vibration exposure. Instead, it is likely to result from the strong dynamic and static joint loading (often in extreme positions of the joint) and the repetitive hand-arm movements (sometimes also repeated minor traumatization) typical for tool manipulation in any heavy labor. Exposure to low-frequency percussion may, however, play a particular etiologic role: damage to the joint cartilage by repeated shocks from the tool, additional articular load (and consequent strain) associated with a vibration-induced increase in the need for joint stabilization and higher gripping forces, the tonic vibration reflex (which increases muscle contraction), and a stronger grip induced when tactile sensibility is diminished by vibration. So far, no investigations have ventured into the great complexity of possible confounders and effect modifiers. -A constitutional susceptibility may be required to produce osteoarthrosis. -The allegation that hand-arm vibration exposure causes an excess prevalence of bone cysts, vacuoles, Kienböck's disease, or pseudarthrosis of the scaphoid has not been validly documented. -Exposure to vibration of higher frequencies (such as from rotating drills, grinders, and chain saws) does not seem to be associated with excess bone and joint pathology. -The observed large variation in the prevalence of skeletal disorders may be explained by biodynamic and ergonomic differences between various occupations.

Pathophysiological aspects of peripheral circulatory disorders in the vibration syndrome.

A review of current knowledge on the pathophysiological aspects of peripheral circulatory derangements in the hand-arm vibration syndrome is presented. Hemodynamic measurements indicate that the primary factor in vibration-induced white finger is an increase in peripheral resistance of finger circulation, present after local and general cooling. The reason for this increase is not known, but it is postulated that there is an excess affinity for the efferent receptors of vasoactive substances and that this affinity is potentiated during local cooling of the digits.

The Stockholm Workshop scale for the classification of cold-induced Raynaud's phenomenon in the hand-arm vibration syndrome (revision of the Taylor-Pelmear scale).

On the basis of experience accumulated over the past few years, a revision has been made in the currently used Taylor-Pelmear scale for the staging of Raynaud's phenomenon in persons exposed to vibration from hand-held tools, while retaining as much as possible of the well-established advantages of the scale for research and its proved usefulness for clinical and medicolegal purposes. The 0T and 0N stages of symptoms have been omitted, together with the parallel disability scale. A separate staging for neurological disorders connected with the syndrome was proposed and accepted at the workshop "Symptomatology and Diagnostic Methods in the Hand-Arm Vibration Syndrome," held in Stockholm in 1986. The criteria descriptions have been changed so as to minimize their reliance on seasonal factors. The new staging system--a stage 0 and four stages (1-4) with attacks of cold-induced Raynaud's phenomenon--clearly defines the differences in the descriptions of the stage criteria in order to improve their clinical usefulness. A numerical scoring based on the extent and distribution of finger blanching was not, however, introduced, whereas a score based on the number of affected fingers on each hand was proposed, considered, and accepted.

A register-epidemiology study on cancer among Swedish printing industry workers.

The Swedish Cancer Environment Registry, a population-based Cancer Registry, has been supplemented with 1960 census data on occupation and industry. This information system was used to generate hypotheses on occupational high-cancer-risk groups and to discuss some methodological problems connected with register epidemiology. By successive exclusion of parts of the original population of printing industry workers with excess risks of lung and cervical cancer it was possible to consider similarities and differences between subgroups. Risk estimates from three different standardization methods agreed well for populations with more than 50 cases. Regional adjustment helped arrive at interpretable risk estimates. The excess risk of cervical cancer disappeared when gainfully employed persons and blue-collar workers were used for reference. After the exclusion procedure there was an excess risk of lung cancer among typographers and lithographers in printing enterprises, especially in some birth-cohorts, due possibly to working exposure environment.

Vasomotor oscillation in vibration-induced white finger.

Vasomotor oscillation at different ambient temperatures, with and without anesthesia of the finger nerves, was studied in six persons with vibration-induced white finger (VWF) and in 10 referents. The power spectral density (PSD) of the Fourier transform of the laser-Doppler flowmeter signal from the finger pad vessels was analyzed. In both groups, the PSD of the vasomotor oscillation in the frequency range of 0.05-0.25 Hz was more pronounced in a cold than in a hot environment. Without finger nerve anesthesia, the oscillations of the referents were significantly greater (p less than 0.01) than those of the VWF subjects (PSD -34.4 dB and -41.6 dB, respectively). With anesthesia of the finger vasomotor nerves, the PSD was reduced in both groups. In the anesthetized finger there was no statistically significant group difference. Thus the myogenic component of the vasomotor activity was the same in the referents as in the VWF subjects. The results show that the autonomic neural influence on vasomotor oscillation in skin of the finger pad is weaker in persons with VWF. This weakness may be a sign of peripheral neuropathy, which may lead to a denervation syndrome causing hypersensitivity of the adrenoceptors to cold.

Circulatory reaction to heat and cold in vibration-induced white finger with and without sympathetic blockade--an experimental study.

Central nervous, sympathetic mechanisms and local factors influencing the vascular response to cold in the finger skin were studied with plethysmographic and laser-Doppler methods in a chamber with controlled temperatures from 45 to about 5 degrees C, with and without sympathetic finger blockade. Blood flow and pressure were assessed after finger occlusion, together with finger heating and cooling, in workers with vibration-induced white finger (VWF) and in healthy persons not exposed to cold or vibration. Finger blood flow at vasodilatation, as measured by finger arterial inflow (FAI) after occlusion was smaller in the VWF group than in the reference subjects both with and without anesthesia, and capillary flux in the anesthetized finger tended to be smaller. At vasoconstriction, with or without anesthesia, the VWF subjects had lower FAI values than the referents. The studied flow and pressure variables differed considerably between the groups. The peripheral resistance of the VWF subjects was higher than that of the referents. This difference was the most pronounced after finger anesthesia. A possible pathogenetic mechanism in VWF is an increase in peripheral resistance due to a local defect in the vessels, with subsequent reduction in flow and intramural pressure.

Pathophysiology and multifactorial etiology of acquired vasospastic disease (Raynaud syndrome) in vibration-exposed workers.

The article reviews available pathophysiological evidence for a multifactorial etiology of the Raynaud type of peripheral circulation disorder in persons exposed to vibration from handheld tools and discusses the consequences this viewpoint may have for diagnostics, preventive work, and research.