A prospective study of the cold response of digital vessels in forestry workers exposed to saw vibration.

OBJECTIVES: To investigate the occurrence of vibration-induced white finger (VWF) and the cold response of digital vessels in a group of 68 forestry workers who underwent a first clinical examination in 1990 and were then reexamined in 1995. METHODS: The forestry workers were divided into three groups: group A (n = 27), active workers who did not have VWF in 1990 and continued to use chain saws; group B (n = 29), workers who did not have VWF in 1990 and retired before 1995; and group C (n = 12), active or retired workers who had VWF in 1990. The subjects underwent a medical interview, a complete physical examination, and a cold provocation test, which were performed by the same physicians at both surveys. The cold test consisted of measurement of the finger systolic blood pressure (FSBP) after local cooling to 10 degrees C, expressed as a percentage of the pressure recorded at 30 degrees C (FSBP%10 degrees). RESULTS: Three new cases of VWF occurred during the follow-up period among workers who had used only antivibration (AV) chain saws. The vasoconstrictor response to cold was unchanged in group A and improved in group B (P < 0.001). A significant decrease in VWF symptoms and abnormal response to cold was observed in group C (P < 0.05). As a result of preventive measures curtailing saw usage time in the VWF workers, the daily vibration exposure in group C was lower in 1995 than in 1990 (P = 0.02). In the retired workers, FSBP%10 degrees was positively related to the time since the cessation of work with chain saws (P < 0.01). CONCLUSIONS: The findings of this follow-up study indicate that a reduction in or cessation of exposure to vibration has a beneficial effect on finger-blanching symptoms and the cold response of digital vessels. The occurrence of new cases of VWF in subjects whose work experience was limited to AV chain saws argues for the maintenance of health surveillance in these workers.

Exposure-response relationship for vibration-induced white finger among forestry workers.

The relation between the occurrence of white finger and vibration exposure was investigated in a group of 222 forestry workers using chain saws. The forestry workers and 195 controls never exposed to hand-transmitted vibration were interviewed by occupational health physicians. The diagnosis of vibration-induced white finger (VWF) was made on the basis of subjective symptoms of finger blanching and the results of a cold test with plethysmographic measurement of finger systolic blood pressure. Vibration was measured on a representative sample of AV and non-AV chain saws. Daily vibration exposure was assessed in terms of 8 h energy-equivalent frequency-weighted acceleration [A(8)]. A lifetime vibration dose was estimated for each of the forestry workers. The overall prevalence of VWF among the forestry workers was 23.4%. Raynaud's phenomenon was discovered in 2.6% of the controls. In the forestry workers, the risk of VWF showed positive increments with each increment of vibration dose, suggesting a monotonic dose-response relationship. The responsiveness to cold in the digital arteries of the forestry workers was also found to increase with increasing vibration dose. The estimated relation between VWF and vibration exposure showed that the expected occurrence of VWF increased in approximately linear proportion to either A(8) (with exposure duration unchanged) or the number of years of exposure (with equivalent acceleration unchanged). In this study of VWF among forestry workers the estimated exposure-response relation showed that if the magnitude of vibration acceleration is doubled, the total duration of exposure should be halved to produce an equivalent effect. On the basis of the assessment of vibration exposure, the estimated risk for VWF in the study population was found to be lower than that predicted by the International Standard ISO 5349. The results of this study tend to support the vibration exposure levels currently under discussion within the European Union.

Dose-response relation for vascular disorders induced by vibration in the fingers of forestry workers.

OBJECTIVES: To study the relation between the prevalence of vascular disorders (white finger) and vibration exposure in a group of 222 forestry workers, of whom 164 (73.9%) had work experience limited to antivibration (AV) chain saws only and 58 (26.1%) had operated both non-AV and AV chain saws. METHODS: The chain saw operators and 195 control workers never exposed to hand transmitted vibration were interviewed with health and workplace assessment questionnaires. The diagnosis of vibration induced white finger (VWF) was made on the basis of subjective symptoms of finger blanching and the results of a cold test with plethysmographic measurement of systolic blood pressure of the finger. Vibration was measured on a representative sample of AV and non-AV chain saws. Daily vibration exposure was assessed as eight hour energy equivalent frequency weighted acceleration (A(8)). A lifetime vibration dose was estimated for each of the forestry workers. RESULTS: The overall prevalence of VWF among the forestry workers was 23.4%. The diagnosis of VWF was made in 13.4% of the forestry workers who handled only AV chain saws and in 51.7% of those who had also operated non-AV chain saws in the past. Raynaud's phenomenon was found in 2.6% of the controls. In the forestry workers, the risk for VWF showed positive increments with each increment of vibration dose, suggesting a monotonic dose-response relation. The responsiveness to cold in the digital arteries of the forestry workers was also found to increase with increasing vibration dose and severity of VWF. The estimated relation between VWF and vibration exposure showed that the expected prevalence of VWF increased almost linearly to either A(8) (with exposure duration unchanged) or the number of years of exposure (with equivalent acceleration unchanged). CONCLUSIONS: In this study of VWF among forestry workers, the estimated dose-response relation showed that if the magnitude of vibration acceleration is doubled, the total duration of exposure should be halved to produce an equivalent effect. On the basis of the assessment of vibration exposure, the estimated risk for VWF in the study population was found to be lower than that predicted by the international standard ISO 5349. These findings suggest a revision of the risk estimates for VWF currently provided by ISO 5349.