Review
The Clinical Features of Hand-arm Vibration Syndrome in a Warm Environment—A Review of the Literature
2012 Volume 54 Issue 5 Pages 349-360
Details
2012 Volume 54 Issue 5 Pages 349-360
The internationally accepted limit values and the health effects of hand-transmitted vibration exposure have been described extensively in the literature from temperate climate countries but not from a tropical climate environment. Objectives: We conducted a systematic review of the health effects of hand-transmitted vibration exposure in tropical countries to determine the characteristics of hand-arm vibration syndrome in a warm environment and compared the findings with the results of the systematic reviews published by the US NIOSH. Methods: We searched major medical databases including MEDLINE, PubMed, Embase, CINAHL, Ovid and Cochrane based on the terms “hand arm vibration syndrome,” “hand transmitted vibration,” “vibration white finger” and “Raynaud” up to January 2011. Only studies conducted in a tropical or subtropical environment were selected for the review. The quality of the selected papers was assessed independently by two investigators using predefined criteria. A standard set of information was abstracted from the papers for review. Results: Only six papers from tropical countries and three papers from subtropical countries were available in the literature. No vibration white finger was reported in the tropical countries. Neurological symptoms were prevalent in the vibration-exposed workers. Finger coldness seems to be an important surrogate for vascular disorder in a tropical environment. Meta-analysis could not be performed due to inadequacy of the information reported in these papers. Conclusions: The current dose-response relationship in ISO5349-1 for hand-transmitted vibration exposure is not applicable to a tropical environment. Further studies on hand-arm vibration syndromes in tropical countries are needed.
The health effects of hand-transmitted vibration (HTV) exposure—hand-arm vibration syndrome (HAVS)—have been described extensively in the literature since the first report of an association between the use of vibrating hand tools and Raynaud's phenomenon by Loriga1) and subsequently by Hamilton2). The United States National Institute of Occupational Safety and Health (NIOSH) has conducted two reviews on studies of HAVS done in different parts of the world from 1969 to 19953, 4). Although the conclusions of both reviews consistently showed a significant association between exposure to HTV and the occurrence of vascular symptoms of HAVS, all studies included in these reviews originated from work done in temperate climate countries where vascular symptoms were commonly seen among vibration-exposed workers.
A national survey conducted by Palmer5) in the United Kingdom reported the prevalence of occupational exposure to HTV was highest in agricultural, construction and manufacturing industries. In Malaysia and Thailand, the total number of workers engaged in these industries was 4.4 and 23.1 million persons respectively based on the 2010 national labor force statistics reports6, 7). The working conditions of the workers using vibrating tools in tropical countries were expected to be of suboptimal standard, as most developing and underdeveloped countries are located in the tropical climate zone. In Malaysia for example, there is no national legislation on HTV exposure for any industry. Besides, most of the workers engaged in these industries were migrant workers who are not covered under national social security schemes. There is no legislative provision on the maintenance and usage of appropriate vibrating tools for workers. Despite the large number of workers engaged in occupations at risk of HTV exposure, the number of cases reported to the Social Security Organisation of Malaysia under the “diseases caused by vibration: disorders of muscles, tendons, bones, joints, peripheral blood vessels or peripheral nerves” was only 34 in 20108). This statistic poses a very important question: is the small number of HAVS notifications attributed to the high incidence of missed diagnosis or reflective of real nonexistence of the condition in the warm environment? Hence, the study of the health effects of HTV exposure in a warm environment is very important to understand the situation and to ensure the appropriate protection of workers using vibrating tools in their daily work.
There are a few reports from tropical climate areas9–11) that have suggested that the clinical features of HAVS in warm climate countries might differ from those of temperate climate countries in terms of the occurrence of vibration white finger (VWF). Hence, data from temperate climate countries may not be applicable to tropical countries in the estimation of the scope of the problems and formulation of preventive measures against HTV hazards in the workplace. The internationally accepted limit values for hand-transmitted vibration (HTV) exposure were determined from the dose-response relationship specified in “ISO 5349-1, Mechanical Vibration—Measurement and Evaluation of Human Exposure to Hand-transmitted Vibration—Part 1: General Requirements (ISO5349-1)” (International Organization for Standardization 2001). The dose-response curve was derived based on Brammer's review12, 13) and was limited to the prevalence of episodic finger blanching from seven epidemiological studies from temperate temperature countries published before 1980. If the clinical features of HAVS differ between the temperate and tropical countries, the ISO5349-1 dose-response curve cannot be applied to HTV-exposed workers from tropical climate countries. Hence, it is important to ascertain the health effects of HTV in a tropical environment in order to decide whether to adopt the existing international standard on human HTV exposure in tropical countries or to formulate a new standard suitable to the tropical environment in an effort to protect workers from the HTV hazard.
There has not been any study done before to compare clinical features of HAVS between temperate and tropical countries. We conducted a literature review of epidemiological studies on HAVS in tropical countries to determine the characteristics of the clinical outcomes of HTV in a warm environment. We compared our findings with the results of the systematic reviews published by the NIOSH3, 4) in the “Discussion” section in this paper.
We searched 23 databases including major databases such as MEDLINE, PubMed, Embase, CINAHL, Ovid and Cochrane for studies published up to January 2011 using medical subject headings and key words based on the following terms: “hand arm vibration syndrome,” “hand transmitted vibration,” “vibration white finger” or “Raynaud.” Broad search terms were used to ensure the inclusion of all relevant studies.
The criteria for inclusion of the papers in the review were as follows: (1) papers published in the English language; (2) epidemiological studies where the primary objective was to determine the prevalence of HAV; (3) exposure information was available; (4) outcome information relevant to HAVS was available with reported prevalence; and (5) the paper was not a case report or case series. The titles of the papers were screened for relevancy and duplicates, and obviously irrelevant studies were eliminated. The abstracts were then reviewed according to the criteria specified above. Papers without an abstract or not meeting the above criteria were excluded. The full text of the remaining papers were then retrieved and reviewed again based on the above inclusion criteria with an additional criterion: (6) the study had to be conducted in a tropical or subtropical climatic environment. Only studies conducted in tropical or subtropical areas were included in the final list of literature for review purposes. In this paper, we define the tropical area as the geographical area on the earth lying between the Tropic of Cancer (latitude 23.5°N) and Tropic of Capricorn (latitude 23.5°S). The reason for applying the criteria to include only the studies from tropical and subtropical areas last was to ensure that we did not miss any relevant studies where the geographical information of the study population might not have been indicated in the title or reported in the abstract. Relevant unpublished work such as conference proceedings and dissertations known to the authors was also included in this review.
The quality of the selected papers was assessed separately by two independent investigators using the seven criteria adapted and modified from Liss and Stock14) and Schweigert15). These criteria were (1) avoidance of bias in the selection of subjects for study group or controls, (2) absence of non-respondent bias, (3) comparability of study and control groups in relation to potential confounding variables, (4) accounting for confounding variables, (5) the use of direct and valid exposure measures, (6) the use of direct and valid outcome measures and (7) application of blinding to assessors. The scoring system used to rate the quality of the papers is presented in Table 1.
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A standard set of information was abstracted from the papers that were finally reviewed. This information included (1) author, (2) date of publication, (3) country, (4) environment temperature, (5) industry, (6) study subject (exposed group and control group), (7) exposure information (type of tools, vibration level and exposure duration), and (8) clinical outcomes (vascular, neurological and musculoskeletal symptoms and the results of hand function tests) with the prevalence rates for each outcome.
The search strategy identified a total of 147 relevant articles. After screening for relevancy and excluding titles without abstracts and those published in a non-English language, 113 abstracts were identified for full text retrieval. All full text papers were reviewed, and studies related to HAVS in tropical or subtropical areas were selected for quality assessment and data extraction. Figure 1 shows the flow diagram of the search strategy and the results of the search.
Flow diagram of the search strategy and search results.
a Included databases = Journals@Ovid, UM Library Journals & LWW, EBM Reviews (Cochrane Database of Systematic Reviews, ACP Journal Club, Database of Abstracts of Reviews of Effects, Cochrane Central Register of Controlled Trials, Cochrane Methodology Register, Health Technology Assessment, NHS Economic Evaluation) Econlit, Geobase and ICONDA.
b Included databases = CINAHL Plus, Dentistry & Oral Sciences Source, Health Business Elite, International Pharmaceutical Abstracts, MEDLINE, PsycARTICLES, Psychology & Behavioral Sciences Collection, SPORTDiscus.
Our literature search identified nine primary studies on which the current review was based. All the papers were epidemiological studies using a cross-sectional design. One of these papers, that of Yamamoto et al.16), should be considered as a case series report. The quality assessment of all the papers is summarized in Table 2. All of the relevant studies identified for this review except for two are of poor quality due to validity deficiencies based on the assessment criteria as specified in the Table 1. Due to the lack of a sufficient number of good quality studies for a meaningful review, all of the studies were considered in this review, and the implications of the limitations are addressed in the “Discussion” section.
| Paper | Avoid selection bias | Avoid non-respondent bias | Comparable study and control groups | Control for confounding bias | Valid exposure measures | Valid outcome measures | Blinding | Overall quality and validity |
|---|---|---|---|---|---|---|---|---|
| Davies et al. 1957 | 1 | 1 | 1 | 1 | 2 | 2 | 1 | P |
| Futatsuka et al. 1991 | 1 | 1 | 1 | 1 | 3 | 2 | 1 | P |
| Futatsuka et al. 1995 | 1 | 1 | 2 | 2 | 1 | 3 | 1 | P |
| Futatsuka et al. 2005 | 1 | 1 | 1 | 1 | 2 | 2 | 1 | P |
| Jamaluddin et al. 2010 | 2 | 1 | 1 | 2 | 3 | 2 | 1 | P |
| Su et al. 2011 | 3 | 2 | 2 | 3 | 3 | 3 | 1 | A |
| Dasgupta et al. 1996 | 1 | 3 | 2 | 1 | 1 | 2 | 1 | P |
| Yamamoto et al. 2002 | 1 | 3 | 1 | 1 | 2 | 3 | 1 | P |
| Nyantumbu et al. 2006 | 3 | 3 | 2 | 1 | 2 | 3 | 3 | A |
A, acceptable; P, poor.
Table 3 shows a summary of all the studies included in this review. From the nine included studies, six were conducted in tropical countries9–11, 17–19), whereas studies from India20), Okinawa, Japan16) and South Africa21) were carried out in subtropical climatic environments. The study conducted in Vietnam by Futatsuka et al.10) was done in the Qui Nhon area located in the southern part of the Vietnam, which has a typical tropical climate. Two other papers published by Futatsuka et al.9, 18) were similar studies whereby the later paper was an extension of the work in the first paper. Hence, strictly speaking, there were only five different epidemiological studies on HAVS done in tropical countries available in the literature.
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Su et al.11) conducted a cross-sectional study among a group of construction workers in Malaysia and reported vibration exposure in terms of daily eight-hour time-weighted average (A (8)) values, years of vibration exposure and lifetime vibration dose. The outcome variables were reported in terms of subjective symptoms (finger color change, finger tingling, finger numbness, musculoskeletal problems of the upper limbs, musculoskeletal problems of the neck, finger coldness, difficulty in handing small objects and difficulty in opening tight jars) and the results of clinical examinations (Tinel's test, Phalen's test, Semmes-Weinstein monofilament test, Rolyan hot and cold discrimination test, two-point discrimination test, Purdue Pegboard test, hand grip strength and neurological examination of upper limbs). There was no special test such as the cold water immersion test, vibrotactile perception test and skin temperature measurement among the subjects. The vibration exposure duration among this group of subjects was rather short, with the majority of the subjects exposed from one to four years.
Jamaluddin et al.19) reported vibrotactile perception threshold levels of a group of shipyard workers in the southern part of peninsular Malaysia and their association with daily A (8) vibration exposure, risk factors and presence of HAVS symptoms. The authors classified the subjects into HAVS and non-HAVS by the presence of neurological symptoms alone, which was not appropriate, as these symptoms cannot confirm the presence of HAVS. The study did not include a comparison group and only reported the prevalence of numbness, tingling and finger whiteness symptoms among shipyard grinders. The average vibration exposure duration among the respondents was two years.
Futatsuka et al.10) studied a total of 73 selected rock drill operators and 29 controls in 50 selected quarry companies in the southern part of Vietnam in 2005. As the subjects were recruited based on the agreement with the workers, employers and workers’ union, selection bias was unavoidable in this study. The authors assessed vibration exposure in terms of vibration acceleration in rock drill operation and total exposure time per working day among the study subjects. The reported outcomes included the relevant subjective symptoms such as coldness of hands and legs, hypoesthesia of fingers, tremor or shivering of fingers, weakness of hands, mobility disturbance of the elbow and shoulder or neck stiffness, and the results of special tests including the vibration and pain sensation level, skin temperature and a nail compression test following cold water immersion. Despite the presence of selection bias, this paper provides estimates on the prevalence of subjective symptoms related to HAVS among the rock drill operators in a tropical environment.
Futatsuka et al.9, 18) conducted two cross-sectional investigations among forestry workers in Papua New Guinea and Indonesia and reported preliminary findings among the foresters in Papua New Guinea in their first paper18) and total findings for both countries in their second paper9). In the first paper, the authors included 16 chain saw operators and 45 controls, whereas in the second paper, a total of 97 chain saw operators and 194 controls were included from both countries. The authors reported skin temperature, finger nail capillary return time and vibration sensation level among the subjects following a cold water immersion test. Although the values of the function test results were reported in the first paper, the authors had further classified the small number of exposed workers into two categories according to the duration of working experience, resulting in too small a number of subjects with a positive outcome in each category for any meaningful data analysis. The authors did not report the results of a cold water immersion test in the second paper. In both papers, the result of principal component analysis was reported and showed a significant association between the duration of chain saw operation and finger nail capillary return time. The authors only reported the prevalence of white finger and finger numbness among the chain saw workers in the second paper.
The earliest work done on HAVS in a tropical climatic environment was carried out by Davis et al.17) in Singapore. The authors investigated 31 dockyard workers, of which one third of them had working experience of more than 15 years, with skin temperature measurement before and after cold water immersion and anteroposterior radiographs of both hands and wrists on subsequent occasions. The results of both tests were reported in a narrative form without detailed presentation of the exact values. The authors selected only three specific controls with different characteristics to describe the differences in the occurrence of vascular symptoms among the dockyard workers and the controls to come to a conclusion. Although the paper has serious methodological deficiencies, it provides some information on the prevalence of HAVS-related symptoms among a group of dockyard workers with a history of using vibrating tools in a warm environment.
The study reported by Nyantumbu et al.21) is of good quality based on the criteria stated in the Table 1. The authors compared the prevalence and severity of HAVS in 156 randomly selected subjects with occupational exposure to vibration in a single South African gold mine against 140 workers with no exposure, and reported the prevalence of HAVS diagnosed by a qualified occupational physician based on the standardized objective tests including thermal aesthesiometry, vibrotactile perception threshold and the cold provocation test following the United Kingdom standardized protocol for HAVS assessment. However, as the study was conducted in a subtropical climatic environment, the presence of intermittent whole body exposure to a winter season might have altered the course of disease experienced by the workers, making it similar to those of workers in temperate climate countries.
Dasgupta and Harrison20) investigated 66 jackhammer drillers and 35 blasters in two open-cast limestone mines in northern India and reported the prevalence of HAVS-related symptoms among the subjects. The authors carried out only two objective assessments— motor conduction velocities and the finger circumference test—on the subjects’ hands as the indicators for neurological and musculoskeletal impairments in the hands of the subjects. Both of these tests were not deployed in any of the other studies included in this review. Hence, we are unable to compare the results of the objective assessments reported in this paper with other papers included in this review. The prevalence of various outcomes reported by the authors does not represent the true picture of the effects of HTV hazard in warm environments because the presence of a winter season might have altered the pathogenesis of the disease as compared with those from equatorial climates.
In the paper published by Yamamoto et al.16), the authors reviewed all 21 medical records of chain saw operators and dam constructors reported as having HAVS by the Okinawa Labour Bureau, Japan. The authors divided the cases into two groups, those who were born and worked mainly in Okinawa and those who were born and worked mainly in other prefectures, and analyzed the results of skin temperature, a nail compression test, vibration perception threshold and the cold water immersion test. There were only six subjects in the first group, and there were 15 subjects in the second group. The authors reported the number of subjects reporting VWF in each group and described the differences in the results of the cold water immersion test. As this study was a review of previous medical records, important methodological deficiencies such as nonrandom sampling, confounding effect, selection bias, recall bias and information bias cannot be avoided. Hence, although this paper suggested a low prevalence of VWF among workers born and working in a subtropical region as compared with those from temperature regions, the results cannot be confidently taken as valid.
Vibration white finger was not reported in the studies done in exclusively tropical environments. Although Futatsuka et al.18) reported one case of white finger among the chain saw operators with more than five years of experience in their paper published in 1991, this result is questionable because the authors also reported two cases of white finger among the workers without chain saw operation experience. In the subsequent paper published in 1995, in which the authors accumulated a bigger sample size of vibration-exposed workers, no VWF was reported. In subtropical countries, Dasgupta and Harrison20) and Nyantumbu et al.21) reported prevalences of finger blanching among the vibration-exposed workers ranging from 5 to 10%. Futatsuka et al.10) and Su et al.11) reported the subjective symptoms of hand and finger coldness as a surrogate for vascular effects among HTV-exposed workers in a tropical environment and reported a prevalence of 20% among rock drill operators and 18% among construction workers respectively. Their terminology, however, does not represent VWF and is likely to overestimate the exact prevalence of HTV-induced vascular disorders.
The prevalence of neurological symptoms (finger tingling, numbness or paraesthesia) was reported in almost all the included studies in the current review and was consistently higher than the prevalence of vascular symptoms. The prevalence ranged from 18 to 68% among the vibration-exposed workers. The reported symptoms for musculoskeletal problems in these papers were very subjective in nature. Different terminologies were used in different papers that might indicate a similar pathology. Hence the reported estimates in these papers cannot be effectively summarized. The prevalence of vascular, neurological and musculoskeletal symptoms is summarized in Table 3.
Only four studies carried out in tropical countries utilized a cold water immersion test in investigation of the hand functions of the vibration-exposed workers9,10,17,18). All of these studies measured finger skin temperature during the cold water immersion test. Out of these four studies, those of Davies et al.17) and Futatsuka et al.9) did not report detailed results for finger skin temperature following the cold water immersion test, whereas Futatsuka et al. in their 1995 paper18) reported the recovery rate of skin temperature at 10 minutes after immersion, and presented a histogram for skin temperature recovery rate of the participants in their 2005 paper10). Futatsuka et al.9, 10, 18) also included a nail compression test and vibration sensation level in the cold water immersion test. The frequency of abnormal results was reported in their first paper in 1991, was not reported in their second paper in 1995 and was presented in a histogram for their vibration sensation level only in the third paper in 2005. Due to inconsistency in data presentation and insufficient information, the results of the cold water immersion tests cannot be aggregated in this review.
Since there were only nine papers found on the epidemiological studies of HAVS in tropical and subtropical countries from our systematic search, all papers were included in the current review despite inconsistent quality. Although all studies were cross sectional in nature, the sampling method and sampled population differed from each other. Futatsuka et al.9, 10, 18), Dasgupta and Harrison20) and Nyantumbu et al.21) compared vibrating tool operators with non-vibrating tool operators; Su et al.11) compared different levels of vibration exposure among a group of construction workers; Yamatomo et al.16) reviewed medical records of chain saw workers and compared those born and working in Okinawa against those from other prefectures; Davies et al.17) investigated a group working as dockyard workers with only three selected controls; and Jamaluddin et al.19) investigated a homogenous group of grinder operators without a comparison group. The exposure information was not reported in all studies. The available exposure and outcome information was not uniform across all studies as shown in Table 3. Hence, we were unable to meaningfully aggregate the results of all studies together and conduct a meta-analysis.
The United States NIOSH has published two systematic reviews on HAVS. The first review was published in 1989 and included 52 cross-sectional studies from Australia, New Zealand, Norway, Finland, Denmark, France, United Kingdom, Sweden, Canada, Italy, United States, Japan, Korea and China from 1969 to 1986. The prevalence of vascular symptoms ranged from 6 to 100%, with 27 studies reporting prevalence rates greater than 40% among workers exposed to hand-arm vibration. The second review was published in 1997 and included 18 studies conducted between 1988 and 1995 from Finland, Canada, Italy, Netherlands, Sweden, United States and Japan. This review found prevalence rates of 15 to 71% for vascular symptoms and a significant relationship between the outcomes and the exposure when comparing the exposed workers with the referents in 13 of the reviewed studies. The result of the current systematic review shows that the prevalence of vascular symptoms of HAVS in tropical countries was very low as compared with the prevalence from temperate climate countries as reported in the two previous systematic reviews done by the NIOSH. None of the studies reported the occurrence of VWF in the tropical environment. Although two papers10, 11) reported higher prevalence of finger coldness among the vibration-exposed workers as compared with controls, the prevalence was low as compared with those in the temperate climate countries. Nevertheless, despite the subjectivity of the term “finger coldness,” this symptom might be an important surrogate indicating the vascular disorders caused by vibration energy among workers living in a warm climatic environment. A previous study22) reported a significant association between the prevalence of finger coldness and the occurrence of Raynaud's phenomenon among workers diagnosed with HAVS. The authors also found a significant association between finger skin temperature and severity of finger coldness reported by the subjects and postulated that the severity of finger coldness is a reflection of the extent of peripheral circulatory vasoconstriction. In the subtropical areas, more objective symptoms such as finger blanching and finger whiteness were reported. In general, the prevalence of vascular symptoms in the subtropical regions was higher than in the tropical areas but lower than in the temperate climate countries.
Although the current review showed that the prevalence of vascular symptoms in the tropical and subtropical countries was lower than in the data from the temperate climate countries published by the NIOSH, a comparison cannot be carried out directly because the exposure and outcome information collection methods were not standardized. A comparative study among vibrating tool workers between a temperate climate country and a tropical climate country using a set of standardized questionnaire and HAVS evaluation modalities would be useful to determine exact differences of the outcomes of HTV between two climatic environments.
From the current review, it is noticed that the prevalence of neurological symptoms in tropical countries differed from the prevalence of vascular symptoms. This supported the suggestion that the neurological and vascular components of HAVS occur and progress independently23). This fact also provides an insight into the question concerning the applicability of dose-response curve as specified in the ISO5349-1 standard. The dose-response curve in the ISO5349-1 documentation was derived based on the occurrence of VWF13) and was used as the basis for the threshold limit value for HTV exposure. Since occurrence of VWF was not seen among workers exposed to HTV in tropical countries, the curve may not represent the outcomes of HTV in a warm environment, indicating that the current version of the ISO5349-1 standard cannot be applied in tropical countries. Hence, there is a need to derive a dose-response curve based on the neurological component of HAVS rather than from VWF alone.
The prevalence of neurological symptoms ranges from 18 to 68% in the tropical environment based on the current review. The type of neurological symptoms reported included finger numbness, tingling, paraesthesia, hypoesthesia, tremor and hyperhidrosis. Although the neurological symptoms of HAVS are subject to variation in perception, a common neurological outcome reported in most of the papers was finger numbness. There were two papers that reported finger tingling and finger numbness separately, but one paper combined finger tingling, numbness and paraesthesia as one entity. In principle, the neurological symptoms of HAVS should comprise a spectrum of clinical symptoms manifested according to the severity of the nerve damage. Hence, it will be more logical to group the symptoms together as finger numbness, tingling and paraesthesia.
We were unable to compare the neurological outcomes to the systematic reviews published by the NIOSH because both NIOSH reports did not address the prevalence of neurological symptoms in detail. The prevalence of neurological symptoms reported by some epidemiological studies24–34)—those conducted by Astrom (Sweden, 2006), Barregard (Sweden, 2003), Jang (Korea, 2002), Bovenzi (Italy, 1994 and 2000), Mirbod (Japan, 1997 and 1999), Palmer (UK, 1998), Anttonen (Finland, 1995), Virokannas (Finland, 1995) and Narini (Canada, 1993)—in temperate weather countries ranged from 12.5 to 78.2%. Although the prevalence of neurological symptoms was almost the same in the tropical and temperate climatic environments, no dose-response relationship based on the neurological symptoms has ever been derived, even in the temperate environment, and we cannot extrapolate the VWF dose-response relationship to that of the neurological outcomes. The subjectivity of the neurological symptoms poses a validity threat to the derivation of dose response relationships based on the symptoms alone. Hence, it is suggested that a dose-response relationship based on the findings from objective tests on the neurological component of HAVS, such as vibrotactile perception threshold, thermal aesthesiometry or nerve conduction test, should be derived for both the tropical and temperate environments.
The clinical features of HAVS in tropical countries differ from those in temperate countries. Vibration white finger was not seen in studies conducted in tropical countries. Rather, the more prevalent condition, which was consistent across all reviewed studies, was finger tingling and numbness. Hence, a dose-response curve as specified in the current version of ISO5349-1 documentation cannot be applied in tropical countries. There is a need to conduct a comparative study to determine the actual differences in the clinical features of HAVS between temperate and tropical climate countries, and to derive a dose-response curve based on the neurological component of HAVS.
The work presented in this paper is part of the research project funded by University of Malaya Research Grant No. RG276/10HTM and a scholarship from the Japan Society for the Promotion of Science (JSPS) RONPAKU Program.
