Search

OBJECTIVES—To investigate the acute effects of the frequency of hand transmitted vibration on finger circulation. A further aim was to investigate whether the frequency weighting assumed in current standards for hand transmitted vibration reflects the haemodynamic changes which occur in the fingers exposed to vibration with different frequencies but with the same frequency weighted acceleration magnitude. METHODS—Finger skin temperature (FST) and finger blood flow (FBF) were measured in the middle fingers of both hands of 10 healthy men. With a static load of 10 N, the right hand was exposed for 15 minutes to the following root mean square (rms) acceleration magnitudes and frequencies of vertical vibration: 5.5 m/s2 at 16 Hz; 11 m/s2 at 31.5 Hz; 22 m/s2 at 63 Hz; 44 m/s2 at 125 Hz; and 88 m/s2 at 250 Hz. These exposures to vibration produce the same frequency weighted acceleration magnitude (5.5 m/s2 rms) according to the frequency weighting included in the international standard ISO 5349. A control condition consisted of exposure to the static load only. Finger circulation was measured before application of the vibration and static load and at fixed intervals during exposure to vibration and a 45 minute recovery period. RESULTS—No significant changes in finger circulation were found with only the static load. The FST did not change significantly during or after acute exposure to vibration. In the vibrated right finger, exposures to vibration with frequencies of 31.5-250 Hz provoked a greater reduction in FBF than did vibration of 16 Hz or the static load only. In the non-vibrated left finger, the FBF measured with vibration at each frequency of 63-250 Hz was significantly lower than that measured with static load only. The reduction in FBF during exposure to vibration with any frequency was stronger in the vibrated finger than in the non-vibrated finger. In both fingers, there was a progressive decrease in FBF after the end of exposure to vibration with frequencies of 31.5-250 Hz. The higher the frequency of vibration, the stronger the decrease in FBF in both fingers during recovery. CONCLUSIONS—Acute exposures to vibration with equal frequency weighted magnitude reduce the FBF in both vibrated and non-vibrated fingers for frequencies between 31.5 and 250 Hz. The extent of digital vasoconstriction after exposure to vibration increases with increasing frequency. The frequency weighting given in current standards tends to overestimate the vasoconstriction associated with acute exposures to vibration frequencies around 16 Hz. Keywords: finger circulation; frequency weighted acceleration magnitude; vibration frequency

OBJECTIVES--To investigate the occurrence of disorders associated with the hand arm vibration syndrome in a large population of stone workers in Italy. The dose-response relation for vibration induced white finger (VWF) was also studied. METHODS--The study population consisted of 570 quarry drillers and stonecarvers exposed to vibration and 258 control stone workers who performed only manual activity. Each subject was interviewed with health and workplace assessment questionnaires. Sensorineural and VWF disorders were staged according to the Stockholm workshop scales. Vibration was measured on a representative sample of percussive and rotary tools. The 8 h energy equivalent frequency weighted acceleration (A (8)) and lifetime vibration doses were calculated for each of the exposed stone workers. RESULTS--Sensorineural and musculoskeletal symptoms occurred more frequently in the workers exposed to vibration than in the controls, but trend statistics did not show a linear exposure-response relation for these disorders. The prevalence of VWF was found to be 30.2% in the entire group exposed to vibration. Raynaud's phenomenon was discovered in 4.3% of the controls. VWF was strongly associated with exposure to vibration and a monotonic dose-response relation was found. According to the exposure data of this study, the expected percentage of stone workers affected with VWF tends to increase roughly in proportion to the square root of A(8) (for a particular exposure period) or in proportion to the square root of the duration of exposure (for a constant magnitude of vibration). CONCLUSION--Even although limited to a specific work situation, the dose-response relation for VWF estimated in this study suggests a time dependency such that halving the years of exposure allows a doubling of the energy equivalent vibration. According to these findings, the vibration exposure levels currently under discussion within the European Community seem to represent reasonable exposure limits for the protection of workers against the harmful effects of hand transmitted vibration.

In a six year follow up study of the handarm vibration syndrome, 62 stoneworkers operating hand held vibrating tools in 10 travertine quarries and mills were first investigated in 1985 and then in 1991. The frequency weighted acceleration of vibration from the rock drills and stone hammers used by the travertine workers exceeded 20 m/s2, indicating a hazardous work activity according to the proposal of the EC directive for physical agents. A clinical examination and a cold provocation test were repeated with the same procedures as those adopted at the time of the first survey. The stoneworkers were divided into groups according to current work state: active stoneworkers who continued to use powered tools during the follow up (n = 21, median exposure time 22 years), and ex-stoneworkers with retirement vibration free intervals of three years (n = 22, median exposure time 27.5 years) and of six years (n = 19, median exposure time 20 years). In the group of active stoneworkers, a 38% onset a new cases of vibration-induced white finger (VWF) was found during the follow up (p < 0.01). Among the retired stoneworkers affected with VWF (n = 24), one recovered from VWF, one showed improvement, 20 remained stationary, and two deteriorated. The ex-stoneworkers experienced no significant change in sensorineural disturbances and a decrease in musculoskeletal symptoms of the upper limbs. At the cold provocation test, the currently active stoneworkers with VWF showed, on a group basis, a delayed finger rewarming time between the two examinations (p = 0.002). An abnormal response to cold provocation persisted in the fingers of the ex-stoneworkers with VWF, even in those reporting subjective improvement. These findings indicate a tendency towards the irreversibility of sensorineural and VWF symptoms in a group of ex-stoneworkers with prolonged exposure to high vibration levels in the past. The increased occurrence of VWF in the active stone workers after a few extra years of vibrating tool usage argues for an urgent implementation of preventive measures in the stone industry.

Many millions of workers are exposed to hand‐transmitted vibration from powered tools and are at risk of developing disorders in the fingers, hands, or arms.1,2,3,4 One consequence of prolonged regular exposure to hand‐transmitted vibration is impaired circulation in the fingers, often evident during or following exposure to cold. The symptoms may be first noticed as abnormally cold fingers, but disorder is often diagnosed from reports of attacks of blanching on the distal, middle, or proximal phalanges. The condition is named “vibration‐induced white finger” from the characteristic attacks of blanching that are assumed to be caused by vibration damage, although the attacks are most often provoked by cold.4 The mechanisms involved in this heightened sensitivity to cold are not known, and so there is uncertainty as to the range of symptoms and signs that characterise the disorder. Although it is clear that hand‐transmitted vibration causes vibration‐induced white finger, there is limited evidence as to the characteristics of vibration that are responsible for the injury. To obtain a number indicating the severity of an exposure to vibration (that is, evaluate the vibration), it is necessary to make assumptions as to the importance of the vibration magnitude, the vibration frequency, the vibration direction, the daily exposure duration, and life‐time exposure duration. Various standards have made such assumptions so as to define uniform methods for evaluating the vibration on powered tools. Having defined a measure of vibration severity, it is possible to assess the acceptability of the vibration, in terms of the probability or severity of disorder. In International Standard 5349‐1 (2001), the evaluation is performed using the root‐mean‐square value of the vibration acceleration after it has been frequency‐weighted (using a weighting called Wh), assuming all directions of vibration to be equally important and all locations of contact with the hand to be equally likely to lead to problems.5 The assessment of vibration severity uses the 8‐hour energy equivalent daily exposure (called A(8)) to predict the years of exposure before 10% of persons are likely to develop the first signs of finger blanching. The frequency weighting inherent in current standards and directives did not evolve from epidemiological studies of the conditions causing vibration‐induced white finger, or from experimental studies of the effects of different frequencies of vibration on relevant physiological responses.6,7 The frequency weighting was largely based on a study of how the discomfort produced by hand‐transmitted vibration depends on the frequency of vibration.8 Some recent epidemiological studies suggest that the frequency weighting may not be optimum and that, at least for the vibration on some groups of common tools, the onset of finger blanching may be predicted with greater accuracy without using frequency weighting Wh.9 The frequency weighting has a large effect on the relative importance of vibration on different tools and, consequently, on the risks of injury and the responsibilities of employers. Improved understanding of the importance of vibration frequency therefore has considerable importance. Contact with the vibration on a tool involves the application of force to the fingers. There are tasks that involve the application of a force without exposure to vibration which do not result in the characteristic symptoms of vibration‐induced white finger, so force alone cannot explain the disorder. However, force may be expected to have some direct mechanical effect on circulation within the fingers. Furthermore, force may alter the transmission of vibration into the fingers and hand: increased force will tend to stiffen the tissues, which will change resonance frequencies and tend to increase the transmission of vibration from the area of contact with vibration. Occupational exposures to hand‐transmitted vibration result in symptoms of vibration‐induced white finger after many months, usually years, of regular exposure to vibration. Laboratory studies have found reductions in blood flow during and following exposure of a finger to vibration. The effects are not restricted to the vibrated finger but are also observed in other fingers, including those on a hand not exposed to vibration. Previous experimental studies by the current authors have explored the effects of the magnitude, frequency, and duration of vibration on finger blood flow using controlled contact areas and controlled contact force.10,11,12 The effects of variations in contact force on finger blood flow have not previously been investigated. This study was designed to investigate whether the force applied by a finger affected finger blood flow and whether the effects of force interacted with the acute effects of vibration. Specifically, it was hypothesised that finger blood flow would be affected by the application of force and that the effects of vibration frequency would be dependent on the force applied to the finger.

OBJECTIVES—To investigate the occurrence of work related respiratory symptoms and to assess the effect of atopy in a group of trainee bakers. METHODS—A prospective study of work related respiratory symptoms among 125 trainee bakers who were investigated with a questionnaire plus skin prick test with wheat flour and α-amylase allergens at baseline and then after 6, 18, and 30 months. RESULTS—At the baseline examination, four students (3.2%) complained of respiratory symptoms (cough and rhinitis) when working with flours and four were skin positive to wheat flour or α-amylase. The incidence of work related respiratory symptoms was 3.4% at 6 months, and the cumulative incidence was 4.8% and 9.0% at 18 and 30 months, respectively. The incidence of skin sensitisation to occupational allergens was 4.6% at 6 months and the cumulative incidence was 4.6% at 18 months and 10.1% at 30 months. The generalised estimating equation approach to longitudinal data showed that work related respiratory symptoms in the study population was significantly associated with a personal history of allergic disease (odds ratio (OR) 5.8, 95% confidence interval (95% CI) 1.8 to 18.2) and skin sensitisation to wheat flour or α-amylase (OR 4.3, 95% CI 1.2 to 14.9). Atopy based on prick test was not related to the occurrence of work related respiratory symptoms over time (OR 1.1, 95% CI 0.3 to 3.8). CONCLUSIONS—Personal history of allergic disease is a predisposing factor for the development of symptoms caused by exposure to wheat flour and may be a criterion of unsuitability for starting a career as a baker. Atopy based on the skin prick test is useful for identifying subjects with allergic disease, but should not be used to exclude non-symptomatic atopic people from bakery work. Keywords: follow up study; wheat flour; α-amylase sensitisation; work related respiratory symptoms

OBJECTIVES: To investigate the changes over a workshift in fingertip tactile perception thresholds in users of impact wrenches exposed to intermittent hand transmitted vibration. A further aim was to assess the relation between acute changes in tactile sensation, sensorineural disorders, and vibration dose. METHODS: The study populations consisted of 30 workers exposed to vibration (16 men and 14 women) and 25 control manual workers (10 men and 15 women). Sensorineural disorders in the fingers and hands were graded according to the staging system of the Stockholm workshop scale. Tactile function was tested by measuring aesthesiometric thresholds (two point discrimination and depth sense perception) and vibrotactile perception thresholds at 16, 31.5, and 125 Hz before and after a workshift. Temporary threshold shift was then calculated as the difference between threshold measures before and after the shift. The measurement and assessment of exposure to vibration were made according to the international standard ISO 5349. The vibration dose accumulated over a workshift (m2s-4h) was estimated for each user of impact wrenches. Daily exposure to vibration was also expressed in terms of eight hour energy equivalent frequency weighted acceleration ((ahw)eq(8) in ms-2 rms). RESULTS: After adjustment for age and alcohol consumption, vibrotactile perception thresholds before exposure were greater in the workers exposed to vibration than in the controls. No differences in aesthesiometric thresholds before the shift were found between the study groups. Sensorineural disorders were mild in the workers exposed to vibration and minor neurological abnormalities were detected at the physical examination. Owing to the intermittent use of impact wrenches, the estimated mean (ahw)eq(8) for the subjects exposed to vibration was low (1.3 ms-2 rms). A significant temporary threshold shift in vibration perception at all test frequencies was found in the workers exposed to vibration but not in the controls. A significant increase in depth sense perception thresholds was found in the men exposed to vibration. The temporary threshold shift in vibration perception at 125 Hz, and to a lesser extent at 16 and 31.5 Hz, was associated with the severity of sensorineural disorders. In the workers exposed to vibration the temporary threshold shift in vibration sense at all test frequencies was positively related to the estimated dose of vibration received over a workshift. No significant relation was found between aesthesiometric threshold changes and vibration dose. CONCLUSIONS: Intermittent exposure to hand transmitted vibration over a workshift can cause a deterioration of tactile perception in the fingers of users of impact wrenches. Acute tactile dysfunction was related to both the estimated dose of vibration and the severity of sensorineural symptoms. The temporary threshold shift in vibration perception suggested that fast adapting skin mechanoreceptors such as Pacinian and Meissner corpuscles were mainly involved in the acute sensory impairment to the fingertips of the workers exposed to vibration. Changes in tactile perception can occur in workers with daily exposure to vibration that is considered to be associated with a minimal risk of adverse health effects induced by vibration.

The relationship between serum concentrations of total IgE and byssinosis and other respiratory symptoms was evaluated in 352 textile workers (90 men, 262 women) at a cotton mill in Friuli-Venezia Giulia, Italy. The subjects were aged from 20 to 61 (mean 44) and the mean duration of employment was 20 years. One hundred and eight subjects (30·7%) were smokers. Only 2% had a positive history of atopy. A standardised questionnaire showed chronic bronchitis in 96 textile workers (27·3%) and byssinosis in 63 (17·9%). The prevalence of respiratory disorders was the same for men and women but was higher in the carding room than in other work areas. Total serum IgE concentrations (RIST, Phadebas) were analysed after log transformation. The geometric mean was 192·7 IU/ml, with no significant difference between the two sexes. This mean concentration of IgE is much higher than that reported internationally for non-atopic subjects, but similar to values found in the Italian population. The IgE concentrations of the workers in the main departments (carding, spinning, and weaving) showed no significant difference. The geometric means were not different in subsamples stratified according to respiratory diseases (cases of pure and cases of mixed forms of chronic bronchitis and byssinosis). A negative result was obtained when IgE concentrations of 289 subjects without byssinosis (¯x = 188·4 IU/ml) and 63 with byssinosis (¯x = 212·6 IU/ml) were compared; there was also no trend when the results were analysed by clinical grade of byssinosis. The same negative pattern occured when the serum IgE concentrations were examined in patients with byssinosis with different grades of chronic change in FEV1. The results of this study support the hypothesis that there is no relationship between total serum IgE concentrations and byssinosis.