Longitudinal study of vibration-induced white finger among coastal fallers in British Columbia.

HUTTON J. Longitudinal study of vibration-induced white finger among coastal fallers in British Columbia. Scand J Work Environ Health 13 (1987) 305-308. Symptom-based vibration-induced white finger was determined longitudinally from a questionnaire administered to 71 full-time fallers exposed 2-4 h daily to generally heavy (> 11 kg), large displacement (> 95 cc) chain saws. The prevalence of Raynaud's phenomenon among 55 fallers (after 16 fallers were excluded because of possible confounders) was 51 010 in 1979-1980. This figure did not differ significantly from the prevalence in 1984-1985 (53 010). Among the 28 fallers reporting symptoms in 1979-1980, seven reported no symptoms in 1984-1985, while four indicated improvement in the severity of symptoms resulting in a decreased stage assessment. Evidence for actual recovery was weak because of discrepancies in the symptom reporting. Reported recovery and improvement in the group with symptoms in 1979-1980 was counterbalanced by a significant 30 010 onset of new symptoms among fallers who were asymptomatic in 1979-1980. Sixof the eight fallers reporting new symptoms were exposed only to antivibration saws, a finding suggesting that the type of saws used in the present investigation is not preventing the onset of new disease. Weighted 4-h equivalent acceleration levels from the handlebars of saws commonly used by the cohort group in 1984 ranged from 4.0 to 12.4 m/s-.

and Japan (2) have shown a significant reduction in the prevalence of symptom-based vibration-induced white finger (VWF) since the introduction of antivibration (AV) saws in the early 1970s. Chain saws typically used in these countries average < 60 cc displacement and weigh < 7 kg with an average 53-em bar.
The primary objective of this research was to evaluate the ameliorative effect of more powerful (> 95 cc) and heavier A V chain saws (> 11 kg with an average 81-cm bar) on VWF in the coastal area of British Columbia, where the prevalence of this disease was 54 070 in 1979 -1980 (I). Fallers are exposed to chain-saw vibration 2 -4 h daily for 10 months of the year in this area, where temperatures reach a low of oto 5°C in January with average precipitation levels of 250-350 em annually. A secondary objective was to measure the vibration levels of large AV saws currently used by fallers in the coastal area of British Columbia.
Reprint requests to: Dr RL Brubaker, Department of Health Care and Epidemiology, The University of British Columbia, James Mather Building, 5804 Fairview Crescent, Vancouver, British Columbia, V6T IW5, Canada.

Methods
A longitudinal study was initiated in 1984-1985 involving 202 fallers from II coastal logging camps on the Vancouver and Queen Charlotte islands. Assistance was obtained from the British Columbia Council of Forest Industries in identifying camps with similar work practices, chain saws, climate and terrain.
All fallers in each camp were invited to participate in order to reduce the chance of self-selection bias. A detailed occupational and symptom questionnaire was administered by a trained interviewer. In addition, an objective vascular test, based on reduction in digital systolic blood pressure after combined cooling (lOcC) and ischemia (4), was performed on the uninjured finger most symptomatic for Raynaud's phenomenon, and the results were compared with those obtained from an uncooled, asymptomatic, uninjured finger (usually the thumb). The digit systolic blood pressure was measured with a Hokanson EC-4 plethysmograph. Digit strain gauges and finger cuffs were obtained from the same manufacturer. The staging for VWF was based on subject symptomatology according to the Taylor & Pelmear classification system (7).
Seventy-one men from the total group of 202 fallers interviewed in 1984-1985 had also been interviewed and tested in an earlier 1979-1980 survey (I). They served as the basis for the longitudinal comparisons made in this paper.
The interview questions on occupational and medical histories, as well as the specific questions on finger symptoms, were similar in both surveys.
The objective vascular test used in the 1979-1980 survey was based on delayed finger rewarming in all 10 digits after release from combined digital cooling and ischemia (I). A change in objective vascular testing in 1984-1985 was based in part on the painful nature of the finger rewarming test.
The vibration measurements were recorded in 1984 from chain saws currently in use at the Cameron logging camp, and they are representative of saws used in the other study locations. The tests were made in accordance with ISO-DIS 5349   Table 2. Prevalence of finger symptoms among the study groups in 1979-1980 and 1984-1985. being recorded in the three prescribed directions. These acceleration levels were recorded on a multichannel frequencymodulated tape deck (B & K model 7003) via a B & K preamplifier (model 2635). The tape-recorded data were analyzed in the laboratory with a Nicolet 660A spectrum analyzer. The spectra obtained were then weighted in accordance with ISO DIS-5349 (3) and expressed as a 4-h weighted acceleration level.

Fallers without vibration-induced white finger in 1979-1980
Among While this change would appear to represent a possible 25 % recovery rate (90 % CI 11.5-38.5) over the five-year period, closer scrutiny of the seven "recovered" cases indicated the following discrepancies:

Operators of both antivibration and nonantivibration chain saws or antivibration saws only
Approximately 33 % of the fallers in this study indicated they had used only AV-type saws. The prevalence and symptomatic stages of VWF among fallers excluded for a history of hypertension, two for a childhood history of polio, one for arthritis of the fingers, three for cervical spine injury requiring fusion, one for Dupuytren's contracture, three for excessive vibration exposure from hobby tools (> 10 h per week), and two for discontinuing faIling during part of the five-year period. There were no obvious cases of primary Raynaud's disease. In addition, exclusions were not specifically made for hand-arm injury, since the prevalence of this condition is high in this occupational group (I).
Most of the results are presented only for the subgroup (N = 55) category after exclusions were made for possible confounders. There was no significant difference in the prevalence of Raynaud's phenomenon and finger tingling and/or numbing over the five-year period when tested with the sign test for matched pairs. The exclusion of 16 fallers with possible confounders, such as excessive hand-arm vibration exposure other than from chain saws, incomplete vibration exposure over the five-year follow-up period, and a history of known possible causes of Raynaud's disease other than vibration exposure, did not alter these results (subgroup category, table 2). Altogether, four fallers were Table 5.  Table 3. Distribution of symptomatic stages among operators of both nonantivibration (Non-AV) and antiv ib ration (AV) chain saws and those using only AV saws . a 1-10 dig its fa iled to rewarm 0.2 "C , 3 m in aft er release fr om ische mia. b Data missin g for o ne objective te st in 1984-1985. c FSP %wc = < 75.

Discussion
Thi s longitudinal follow-up of VWF using symptom histor y as a mean s of temporal assessment is complicated by the follo wing factors: the unr eliability of sympto m reporting, the fluctua ting co urse of the Non -AV +AV AVonly ope rato rs o perators 1979-1984-1979-1984-1980 1985 1980 1985 ----

Chain-saw vibration testing
Test resul ts for th e two chain saws most commonly used for coa stal falling in British Columbia are shown in ta ble 5. All the tests were ma de with a bu ckin g cut on the sa me log by the sa me ope rator. Eac h value quoted was derived from 50 averages taken dur ing one cut to obtain the spectru m fro m which th e weighted levels were calc ulated . The results are indi cat ed for both the fron t and rear handles and the levels indicated were those corres ponding to the dir ection of maximum vibra tion. As noted, the acceleration levels ranged from 4.0 to 12.4 m/ s'. A typical spectrum is shown in figure   1 (  disease, and the lack of agreem ent between symptom reporting and objective assessment. In addition there are oth er important confounders, as described by Riddle & Taylor (6), such as changes in life-style or work practices and symptom learning, which can lead to an under-or overesti-nation o f symptoms. Despite the se constraints, it appears that the use of large AV saws is not prevent ing the onset of new cases of VWF among coastal fallers in British Columbia. In fact , 72 070 of the workers expo sed only to AV saws in this study developed VWF within a relativel y short latenc y period of 4.2 (SO 2.3) year s. Based on nomogram predictions made according to ISO-DIS 5349 (3), the large AV chain saws currently used by coastal faller s in British Columbia might be expected to lead to the onset of new symptoms for 50 % of new users within 5 -II years. This estimate was based on vibration levels of 7 -12.4 mis' (recorded from the handle exhibiting the highest vibration) from the two commonly used chain saws field tested in this study.
A significant onset of new disease was not observed within the five-year period however among operators originally exposed to non-AV saws, a finding suggesting that a plateau may have been reached. In fact there is some evidence indicating a slight improvement (15 %) or lessening of symptoms for fallers in this group. Evidence for actual recover y from symptoms is weak because of discrepancies in the symptom reporting. It is hoped that the additional serial measure-308 ments now being obtained on an annual basis may help clarify symptom tr ends for the non-A V + AV group .