Vibration white finger, digital blood pressure, and some biochemical findings on workers operating vibrating tools in the engine manufacturing industry

A clinical and laboratory investigation was carried out on 76 operators using pneumatic hand grinders and impact wrenches in the engine manufacturing industry. Twenty-two vibration-exposed workers (28.9%) had no symptoms in the hands (stage 0 of the Stockholm Workshop scale), 34 (44.7%) were affected with sensorineural disturbances in the fingers (stage SN), and 20 (26.3%) suffered from vibration white finger (VWF stages 1-2-3). In the vibration-exposed operators and in 30 comparable referents not exposed to vibration, finger systolic blood pressure (FSP) was measured on a test finger and on a control finger after digit cooling to 30 degrees C and 10 degrees C. The results of the cold provocation test were expressed as percent change of FSP by cooling the test finger from 30 degrees C to 10 degrees C (FSP%t, 10 degrees) and as digital/brachial pressure index during local cooling at 10 degrees C (DPIt, 10 degrees). After cold provocation the mean values of FSP%t, 10 degrees and DPIt 10 degrees were more significantly reduced in the vibration-exposed workers with VWF than in those without VWF and the referents (p less than 0.001). The cold provocation test was found to differentiate between VWF subjects with stages 1-2 and stage 3 (p less than 0.02). It is concluded that the measurement of FSP combined with finger cooling is a useful laboratory test to diagnose objectively Raynaud's phenomenon of occupational origin. The vibration-exposed workers and the referents were also tested for serum levels of immunoglobulins and complement and for daily excretion of urinary free catecholamines. Between the reference and vibration groups no differences in the mean values of the immunologic parameters and urinary catecholamines were found. The meaning of these findings is discussed.     

A critique of a UK standardized test of finger rewarming after cold provocation in the diagnosis and staging of hand-arm vibration syndrome

BACKGROUND: Accurate diagnosis and staging of hand-arm vibration syndrome (HAVS) is important in health surveillance of vibration-exposed workers and the substantial number of related medico-legal cases. The measurement of the rewarming rate of fingers after cold provocation to the hands (CPT) has been suggested as a useful test in diagnosing HAVS. AIM: To investigate the diagnostic value of a standardized version of the CPT test using a 15 degrees C cold challenge for 5 min applied in the recent compensation assessment of UK miners. METHODS: Analysis of a subset of UK miners assessed at our unit, together with data from a small repeatability study of the standardized CPT in normal subjects. RESULTS: Rewarming time in the CPT was significantly lower in those subjects classified as vascular Stockholm stage 0 compared with Stockholm stages 1-3 combined, but did not discriminate between the stages of abnormality. Using the suggested cut-off in the CPT test, the sensitivity and specificity were calculated as 43 and 78%, respectively. Receiver operator characteristic analysis suggested that the rewarming time of highest accuracy gave a sensitivity of 66% and specificity of 59%. In 10 miners who reported unilateral hand blanching, there was no significant difference in CPT measurements between blanching and non-blanching hands. Repeat CPT measurements in normal subjects suggested mean differences of 52 and 107 s for each hand, and the Bland-Altman coefficient of repeatability was approximately 600 s for all fingers. CONCLUSION: Single application of this standardized CPT test may have limited value in diagnosing the vascular component of HAVS in an individual.     

Relation of haemostatic function, neurovascular impairment, and vibration exposure in workers with different stages of vibration induced white finger.

Haemostatic function and neurovascular symptoms were investigated in 67 workers exposed to vibration and 46 comparable referents. Of these 65.6% of vibration workers complained of neurological disturbances (stages 0T, 0N of Taylor's classification for vibration induced white finger (VWF) and 20.9% suffered from Raynaud's phenomenon (stages 1-2-3). The severity of the staging symptoms showed a close relation with an index of vibration dose computed on the basis of vibration measurement and individual exposure time. Indices of platelet aggregation, both in vitro and in vivo, antithrombin III, fibrinogen and fibrinopeptide A levels were not different in the exposed workers compared with the referents. No relation was found between haemostatic parameters and the severity of VWF. Exposed workers responded to a cooling procedure with a more pronounced vasoconstriction in the digital vessels than the referents, as indicated by delayed recovery time of finger skin temperature after the cold test. These findings suggest that both in the early stages (0T, 0N) and in more severe stages of VWF (stages 1-2) cold induced hyperreactivity in the digital vessels and Raynaud's syndrome are vascular disorders of functional origin occurring without any prethrombotic alterations.     

Relation of haemostatic function, neurovascular impairment, and vibration exposure in workers with different stages of vibration induced white finger

Haemostatic function and neurovascular symptoms were investigated in 67 workers exposed to vibration and 46 comparable referents. Of these 65.6% of vibration workers complained of neurological disturbances (stages 0T, 0N of Taylor's classification for vibration induced white finger (VWF) and 20.9% suffered from Raynaud's phenomenon (stages 1-2-3). The severity of the staging symptoms showed a close relation with an index of vibration dose computed on the basis of vibration measurement and individual exposure time. Indices of platelet aggregation, both in vitro and in vivo, antithrombin III, fibrinogen and fibrinopeptide A levels were not different in the exposed workers compared with the referents. No relation was found between haemostatic parameters and the severity of VWF. Exposed workers responded to a cooling procedure with a more pronounced vasoconstriction in the digital vessels than the referents, as indicated by delayed recovery time of finger skin temperature after the cold test. These findings suggest that both in the early stages (0T, 0N) and in more severe stages of VWF (stages 1-2) cold induced hyperreactivity in the digital vessels and Raynaud's syndrome are vascular disorders of functional origin occurring without any prethrombotic alterations.     

Significance of finger coldness in hand-arm vibration syndrome

Objectives To evaluate the relationship between subjective symptoms of coldness in fingers and peripheral circulation in patients with hand-arm vibration syndrome (HAVS). Methods Thirty-five male patients confirmed to have HAVS as an occupational disease took part in this study. Their mean age was 62 years (SD 5) and all were chain-saw operators exposed to vibration for an average of 25 years. Their annual health examination included the history of their daily habits (smoking, drinking, and therapeutic exercise), report of subjective symptoms such as coldness, numbness and tingling in the fingers, and a physical examination; laboratory tests consisted of skin temperature measurement, and pain and vibration perception under conditions of cold provocation. A frequently used method of cold provocation, immersion of the left hand up to the wrist in water of 10°C for 10 min, was used. Results Finger coldness was classified into 3 groups according to its severity: mild group (n=8), moderate group (n=17) and severe group (n=10). There was no significant difference in age or occupational background between the groups. A significant association was found between finger coldness and prevalence of Raynaud's pheno menon (p<001, χ²). The mean skin temperature was significantly lower with the severity of finger coldness (ANOVA, p<0.05). In the cold provocation test, there was no significant difference between skin temperature and coldness at 5 min and 10 min after immersion, though a difference was observed immediately after immersion. No significant difference was observed in the relationship between finger coldness and vibrotactile threshold before, during or after the cold provocation test. Conclusions The severity of coldness in the fingers is significantly related to skin temperature. The severity of finger coldness reflects the extent of peripheral circulatory vasoconstriction. Coldness in the fingers may be a good warning of potential problems in peripheral, circulatory function.     

Interpretation of the finger skin temperature response to cold provocation

Objectives: To compare alternative methods of interpreting the response of finger skin temperature (FST) to cold provocation for the detection of the abnormal cold response observed in vibration-induced white finger (VWF). Method: The FST response to cold provocation was measured in 36 male subjects: 12 office workers, 12 manual workers and 12 manual workers with symptoms of VWF. The FSTs were monitored continuously on the distal phalanges of all five fingers of a test hand for 2 min before, for 5 min during, and for 10 min following, immersion of the test hand in water at 15 °C. Of the fingers investigated, 147 were reported not to exhibit blanching and 33 were reported to exhibit blanching. Twenty-one alternative methods of interpreting the response of FSTs to cold provocation were assessed. These were grouped as: (1) areas above the response profile (i.e. the area above the curve showing the FSTs as a function of time during cooling and recovery), (2) areas below the response profile, (3) absolute temperatures during and following cold provocation, (4) percentage differences in FSTs, (5) the times taken for FSTs to rise by specified amounts and (6) rates of change of FSTs. Differences in the response to cooling between those fingers reported to blanch and the fingers not reported to blanch were tested, and receiver operating characteristics (ROCs) were used to compare the sensitivity and specificity of the various measures to symptoms of VWF. Results: The areas above the response profile, areas below the response profile, percentage FSTs, absolute FSTs and rates of change of FSTs tended to discriminate between healthy and unhealthy subjects on a group basis. However, some of these methods of interpreting the FST response to cold provocation did not show a high sensitivity or specificity to vascular dysfunction on individual fingers. The area above the response profile, the percentage of initial temperature at the fifth minute of recovery and the maximum temperature during the 10-min recovery period, were found to show the highest sensitivity and specificity to symptoms of vascular dysfunction. Conclusions: The method chosen to interpret the FST response to cold provocation affects the ability of the test to detect an abnormal cold response. The area above the response profile, the percentage of initial temperature at the fifth minute of recovery and the maximum temperature achieved during a 10-min recovery period appear to be the most suitable measures for monitoring vascular function in workers exposed to hand-transmitted vibration. It is suggested that the FST response to cold provocation should be interpreted with respect to the state of initial blood flow. Received: 12 June 2000 / Accepted: 28 December 2000     

振动性白指—局部受冷和振动负荷后的末梢循环表现

本研究分为三个组:(1)振动白指组(29例);(2)振动无白指组(105例);(3)对照组(60例)。 研究表明:振动白指组冷水试验的白指再现率为10％,而振动无白指组和对照组无一例出现白指;Ⅰ期振动性白指患者的皮温恢复时间延长者占40％,而Ⅱ期和Ⅲ期振动白指患者皮温恢复时间延长者均为100％;振动白指组的指血流图平均波辐高度冷水试验后显著低于冷水试验前(P<0.01),而振动无白指组和对照组没有这种差异。 本文讨论上述试验在振动性白指诊断中的意义。     

Laser Doppler imaging of skin blood flow for assessing peripheral vascular impairment in hand-arm vibration syndrome

The objective of this study was to evaluate the usefulness of laser Doppler imaging (LDPI) of the skin blood flow for assessing peripheral vascular impairment in the hand-arm vibration syndrome (HAVS). The subjects were 46 male patients with HAVS, aged 50 to 69 yr, and 31 healthy male volunteers of similar age as controls. A cold provocation test was carried out by immersing a subject's hand on his more severely affected side into cold water at a temperature of 10 degrees C for 10 min. Repeated image scanning of skin blood flow of the index, middle, and ring fingers was performed every 2 min before, during, and after the cold water immersion using a PMI-II laser Doppler perfusion imager. The mean blood perfusion values in the distal phalanx area of the fingers were calculated on each image. The patients suffering from vibration-induced white finger (VWF, n=20) demonstrated significantly lower skin blood perfusion at each interval of the test as compared with those without VWF (n=26) and the controls (p<0.01, ANOVA). The blood perfusions in the HAVS patients were associated with the severity of the symptoms as classified by the Stockholm Workshop scale for vascular staging. When a subject was considered to be positive if any of the tested fingers showing a decreased blood perfusion and/or a delayed recovery pattern, the sensitivity was 80.0%, and the specificity was 84.6% and 93.5% for patients without VWF and the controls, respectively. These results suggest that the LDPI technique could provide detailed and accurate information that may help detect the existence of impaired vascular regulation to cold exposure in the fingers of workers exposed to hand-transmitted vibration.     

Preliminary study on the assessment of peripheral vascular response to cold provocation in workers exposed to hand-arm vibration using laser Doppler perfusion imager

Measurements of changes in finger skin blood flow with laser Doppler perfusion imaging (LDPI) in response to cold provocation test (10 degrees C, 10 min) were performed in 12 men suffering from vibration induced white finger (VWF) and 13 exposed controls. The mean perfusion values in both groups reduced markedly as a result of immersion of the hand in cold water. In the controls, however, the mean value increased gradually until the end of the cold provocation, while that in the VWF subjects remained at the lowest level. After removal of the hand from the cold water, the skin blood perfusion in the controls recovered rapidly and nearly reached the baseline value. In the VWF subjects, it had a slight increase immediately following the cold immersion but no tendency to rise as the time span increased. Analysis of covariance controlling for possible confounders revealed that the VWF subjects had significantly lower perfusion values compared to the controls in the last several minutes of the cold provocation and the following recovery. These findings suggest that the LDPI technique enables visualizing and quantifying the peripheral vascular effects of cold water immersion on the finger skin blood perfusion and thus has the potential of providing more detailed and a&curate information that may help detect the peripheral circulatory impairment in the fingers of vibration-exposed workers.     

手臂振动对手部红外图像影响的研究

对３７名手臂振动作业工人和３０名健康对照工人,在冷水试验和振动负荷试验前后,以ＫＹ－３３３型远红外摄像仪进行手都红外摄像,比较研究其图像变化。结果表明,试验前两组基础指温差异不显著;试验后接振组指温下降明显。复温时间延长,冷试后５ｍｉｎ、１０ｍｉｎ;振动负荷后即刻、５ｍｉｎ差异显著。红外图像的改变,有助于振动职业危害的亚临床研究。     

Prevalence of vibration-induced white finger in fluorspar mines in Weardale.

A combined epidemiological and clinical study of vibration-induced white finger (VWF) was carried out involving 115 men in four fluorspar mines. The overall prevalence of VWF was found to be 50% among 42 vibration-exposed subjects, while that of constitutional white finger (CWF) was 5-6% in all men studied. The VWF latent interval was 1-19 years with a mean of 5-6 years. An association was observed between the exposure time and VWF stages which included 18 men in Stage 0, three in the intermediate Stage of 0T/0N, five in Stage 2 and 16 in Stage 3; no men were seen at Stage 1. Among those with VWF in Stage 3, the index, middle and ring fingers were affected in both hands and the little fingers and thumbs were last to be involved. Clinically, on general examination, apart from vibration-induced white finger, the men in the 'vibration' group were not as healthy as those in the 'control' group. The circumference of the index fingers was not significantly different for the different groups. Neurological tests showed that the ridge test and, to a lesser extent, the two-point discrimination and the light touch tests, could be regarded as useful for the diagnosis of VWF.     

A four-year follow-up study on subjective symptoms and functional capacities in workers using hand-held grinders.

Fifty-three grinders in the metal industry were re-examined 4 years after their first examination. Information about age, occupation, daily vibration exposure, drinking and smoking habits, and presence of subjective symptoms such as vibration-induced white finger (VWF), and numbness and pain in the fingers was collected during the first and second examination. Cold provocation test (10 degrees C/10 min) was also employed to evaluate disturbances in the peripheral circulatory and peripheral nerves in all subjects. The frequency-weighted vibration acceleration of various types of hand-held tools was measured. There was no subject with VWF at the first examination; however, during the course of follow-up, two cases (3.8%) of VWF with latent interval of more than 25 years were diagnosed. Prevalence of numbness in the fingers and shoulder stiffness was significantly higher at the second examination. When the prevalence of subjective symptoms was tested by the subjects' total operating time (TOT) during the 4-year follow-up period, those whose TOT was equal to or more than 2500 hours showed higher prevalence compared to the other subgroup. The paired values of recovery rate of finger skin temperature and vibration sensation threshold after the cold water immersion test were significantly different at the first and second examination. On average, the diminution of hand-grip force during the 4-year follow-up course was 7.4%; the difference being significant at 0.01 level. Significant differences in the paired data of pinching power and tapping ability could be detected. The frequency-weighted vibration acceleration of various tools was in the range of 1.1-4.6 m/s2. It was concluded that: (1) prolonged occupational exposure to the vibration of hand-held grinding tools should be considered as a risk factor causing disturbances in the hand-arm system of the operators; (2) the results of recovery rate of finger skin temperature and the vibration sensation threshold seemed to be appropriate indicators for the assessment of peripheral vascular and peripheral nerve disturbances in workers exposed to hand-arm vibration; and (3) to reduce the subjects' physical stress, attention should be paid to ergonomic factors.     

A 4 degrees C-1 min method of cold water immersion test for peripheral circulatory function in fingers]

To assess the validity of a new simplified cold water immersion test (4 degrees C-1 min method) for peripheral circulatory function, comparison was made with the conventional method (10 degrees C-10 min method). These two different methods of cold immersion test were applied to 23 patients with vibration disease and 24 healthy men. Observation was made on finger skin temperature by a thermistor and complaints in the hand by a 5-step self-reported scale method every minute during the test. The patterns of recovery of skin temperature after cold immersion in each group were similar in both methods. Pain in the hand in the 4 degrees C-1 min method was less than that in the 10 degrees C-10 min method. The recovery rate at 5 min in the patients with Raynaud's phenomenon was lower than that in those without Raynaud's phenomenon in the 4 degrees C-1 min method (p < 0.01). However, no significant differences were noted in 10 degrees C-10 min method. The results suggest that the new method is feasible in detecting the response of vasodilation after immersion. In the recovery rate at 5 min after immersion, near values of the sensitivity and specificity were observed between 50% cut-off values in the 4 degrees C-1 min method and 30% value in the 10 degrees C-10 min method. Thus, the 4 degrees C-1 min method is considered to be more useful to evaluate the physiological response after cold immersion than the 10 degrees C-10 min method.     

Normative data for vascular and neurological tests of the hand-arm vibration syndrome

OBJECTIVES: To assist occupational health professionals to interpret the results of standardised tests for components of the hand-arm vibration syndrome by presenting data for healthy subjects and identifying the effects of some of the confounding variables. METHOD: Thermal thresholds, vibrotactile thresholds, the finger skin temperature (FST) response to cold provocation and percentage finger systolic blood pressures (%FSBP) were measured by standardised procedures. Normative data were obtained for healthy men of working age (17-62 years) during 237 experimental sessions encompassing ten different studies. Hot thermal thresholds and cold thermal thresholds were assessed independently with 38 subjects; 152 measurements of both hot and cold thresholds were made. Vibrotactile thresholds were measured at several locations on 81 subjects, giving a total of 216 measurements at 125 Hz and at 31.5 Hz. The FST response to cold provocation at 15 degrees C was monitored by thermocouples throughout a 2-min settling period, a 5-min immersion period and a 10-min recovery period. A total of 302 measurements was made on 70 subjects. The %FSBPs were measured in four test fingers and one reference finger by strain-gauge plethysmography. Measurements were made on 97 subjects. A total of 351 measurements was made at 15 degrees C, with 341 measurements at 10 degrees C. RESULTS: Normative data and some example normal limits are presented from the current data set and from data presented in other studies. Age was found to influence thermal thresholds, vibrotactile thresholds and the FST response to cold provocation; older subjects exhibited deteriorated vascular and neurological function. Room temperature was found to influence %FSBPs and the FST response to cold provocation; warmer environments resulted in improved vascular response to cold. Outdoor temperature had a small effect on the FST response to cold provocation and on the vibrotactile thresholds. Thermal thresholds showed some influence of smoking habits and of the FST measured prior to testing. For all four tests, any differences between measurement locations were small and there were no differences between left-handed and right-handed subjects. CONCLUSIONS: The current data can assist occupational health professionals to interpret the results of the standardised tests. Comparison with the current data is considered valid for men of working age. Age and room temperature should be recognised as being capable of causing changes in neurological and vascular function.     

Circulatory disturbances of the foot in vibration syndrome

Summary Circulatory disturbances of the foot in patients with vibration syndrome were studied by measuring the skin temperature of both index fingers and great toes through a 3-min immersion of the right foot in cold water at 10°C. Subjects included 11 patients with vibration-induced white finger (VWF) [VWF(+) group], 12 patients without VWF [VWF(–) group], and 20 healthy referents not exposed to vibration. Patients were all male chain saw operators who had scarcely been exposed to vibration of the foot. The prevalence of coldness felt in the upper and lower extremities was > 90% in the VWF(+) group, about 60% in the VWF(–) group, and < 10% in the referents. The extent of the coldness was greatest in the VWF (+) group. The skin temperature of both fingers and toes was lowest in the VWF(+) group, somewhat higher in the VWF(–) group, and highest in the referents both before and after immersion. These findings indicate that patients with vibration syndrome, especially those with VWF, have circulatory disturbances in the foot as well as in the hand. The disturbances in the foot may be related to long-term repeated vasoconstriction in the foot induced by hand-arm vibration through the sympathetic nervous system.     

Normal values for finger systolic blood pressures in males and females

Objective

To compare finger systolic blood pressures in males and females and in younger and older persons and provide normal values for all four fingers in younger and older males and females.

Methods

Eighty healthy subjects participated in the study: 20 males and 20 females aged 20–30 years, and 20 males and 20 females aged 55–65 years. Finger systolic blood pressures (FSBPs) were measured using strain-gauge plethysmography following local cooling at 30 and 10°C in accord with International Standard 14835-2. The FSBPs were measured simultaneously in the thumb and the four fingers of the dominant hand and the percentage changes in finger systolic blood pressures (%FSBPs) due to the cold provocation were calculated.

Results

The median finger systolic blood pressures increased with increasing age in both females and males, with the increase highly significant at 30°C but not at 10°C. The %FSBPs were not significantly affected by the age of males, but were significantly lower in older females than younger females. The FSBPs were lower in females than in males at 30°C but there was no significant difference between genders at 10°C. The %FSBPs were higher in younger females than younger males, but only significantly higher in the middle finger and there were no significant differences between the genders in the older age group. There were only minor differences between the four fingers in the FSBPs at 30 and 10°C. The %FSBPs across the four fingers were similar in the younger subjects and in the older females, but varied with finger in the older males.

Conclusion

Although there are some differences in the %FSBPs associated with age, gender, and finger, the differences may be sufficiently small to use a single value criterion when deciding on abnormalities in FSBP associated with cold provocation for persons aged 20–65 years.

     

Cold-provocation testing for the vascular component of hand-arm vibration syndrome in health surveillance

The aim was to investigate whether the use of infra-red thermography (I-R) and measurement of temperature gradients along the finger could improve the diagnostic accuracy of cold-provocation testing (15 degrees C for 5 min) in vascular hand-arm vibration syndrome (HAVS). Twenty-one controls and 33 individuals with stages 2/3V HAVS were studied. The standard measurement of time to rewarm by 4 degrees C (T4 degrees C) and temperature gradients between the finger tip, base and middle (measured using I-R) were calculated. Receiver Operating Characteristics (ROC) analysis to distinguish between the two groups revealed that for T4 degrees C the area under the ROC curve was not statistically significantly different from 0.5 (0.64 95% confidence interval 0.49-0.76). The difference between the tip and middle portion of the finger during the sixth minute of recovery was the most promising gradient with an area of 0.76 (95% confidence interval 0.62-0.87), and sensitivity and specificity of 57.6% and 85.7% respectively. However, this was not significantly different from that for the time to rewarm by 4 degrees C. In conclusion, the cold-provocation test used in this study does not appear to discriminate between individuals with stage 2/3V HAVS and controls and this is not improved by the measurement of temperature gradients along the fingers using I-R.     

Raynaud's phenomenon of fingers and toes of miners exposed to local and whole-body vibration and cold

Summary In a study of 27 underground miners exposed to hand or whole-body vibration, cold or other vasoconstrictive environmental factors, higher prevalences of Raynaud's phenomenon in both fingers and toes were found than in a control group not exposed to vibration. There were no Raynaud-like phenomena among miners not exposed to vibration. There was a positive correlation between the two locations. This may mean a general susceptibility of vasospasm, but it seems more probable that the disorders are caused by vibration exposure to fingers and toes.     

正常人手部温度分布及冷水试验影响的红外图像分析

应用ＫＹ－３３３型远红外摄像仪,对３０名正常人在两种冷水试验前后手部皮肤温度分布进行研究。结果表明,正常人在两种冷水试验前后同手不同手指之间及左右手相应手指之间温度比较,差异无显著性。手背皮温在冷试后即刻及５ｍｉｎ时显著高于各手指皮温,而１５ｍｉｎ后又低于手指皮温。说明正常人左右手之间及不同的手指之间的皮温没有差异,可以测量某一手指皮温来代替手部皮温。     

Changes in cold-induced vasodilatation, pain and cold sensation in fingers caused by repeated finger cooling in a cool environment

To examine how repeated cooling of fingers with a rest pause schedule at work affects cold-induced vasodilatation (CIVD), pain and cold sensation in fingers, six healthy men aged 21 to 23 years immersed their left index fingers six times in stirred water at 10 degrees C for 10 minutes. After each cold-water immersion of the fingers, 5-minute rest pause was taken to observe the recovery process of the indicators. This cold-water immersion/rest pause test was carried out in a range of three ambient temperature conditions: 30 degrees C (warm), 25 degrees C (thermoneutral), and 20 degrees C (cool) as experienced in daily life. At the ambient temperatures of 30 degrees C and 25 degrees C, marked CIVD response occurred and the CIVD reactivity did not significantly change upon repetition of cold-water immersion. The lowered finger skin temperature also tended to recover quickly to the pre-immersion level during each post-immersion rest period. At the ambient temperature of 20 degrees C, however, the CIVD response weakened continuously upon repetition of immersion and almost disappeared during the final immersion. The recovery of finger skin temperature during each post-immersion rest was gradually delayed upon repetition of immersion. At every ambient temperature, finger pain and cold sensation induced by each cold-water immersion significantly decreased upon repetition of immersion and completely disappeared during each post-immersion rest period. Oral temperature during the experiment showed no significant change at the ambient temperatures of 25 degrees C and 30 degrees C, but it decreased significantly at the ambient temperature of 20 degrees C. These results suggest that in a cool work environment where the body core temperature is liable to decrease, repeated finger cooling may weaken CIVD reactivity and delay the recovery of finger temperature during post-immersion rest periods. In such lower ambient temperature work conditions, subjective judgements such as the decrease in finger pain and cold sensation during repeated finger cooling and the absence of them during post-immersion rest may not be reliable indicators for monitoring the risk of progressive tissue cooling and frostbite formation.