The influence of vibration on seated human drowsiness.

Although much is known about human body vibration discomfort, there is little research data on the effects of vibration on vehicle occupant drowsiness. A laboratory experimental setup has been developed. Vibration was applied to the volunteers sitting on the vehicle seat mounted on the vibration platform. Seated volunteers were exposed to a Gaussian random vibration, with 1-15 Hz frequency bandwidth at 0.2 ms(-2) r.m.s., for 20-minutes. Two drowsiness measurement methods were used, Psychomotor Vigilance Test (PVT) and Karolinska Sleepiness Scale (KSS). Significant changes in PVT (p<0.05) and KSS (p<0.05) were detected in all eighteen volunteers. Furthermore, a moderate correlation (r>0.4) was observed between objective measurement (PVT) and subjective measurement (KSS). The results suggest that exposure to vibration even for 20-minutes can cause significant drowsiness impairing psychomotor performance. This finding has important implications for road safety.

A cross sectional study on hand-arm vibration syndrome among a group of tree fellers in a tropical environment.

This study aimed to explore the clinical characteristics of hand arm vibration syndrome (HAVS) in a group of tree fellers in a tropical environment. We examined all tree fellers and selected control subjects in a logging camp of central Sarawak for vibration exposure and presence of HAVS symptoms utilizing vibrotactile perception threshold test (VPT) and cold water provocation test (CWP). None of the subjects reported white finger. The tree fellers reported significantly higher prevalence of finger coldness as compared to the control subjects (OR=10.32, 95%CI=1.21-87.94). A lower finger skin temperature, longer fingernail capillary return time and higher VPT were observed among the tree fellers as compared to the control subjects in all fingers (effect size >0.5). The VPT following CWP of the tree fellers was significantly higher (repeated measures ANOVA p=0.002, partial η(2)=0.196) than the control subject. The A (8) level was associated with finger tingling, numbness and dullness (effect size=0.983) and finger coldness (effect size=0.524) among the tree fellers. Finger coldness and finger tingling, numbness and dullness are important symptoms for HAVS in tropical environment that may indicate vascular and neurological damage due to hand-transmitted vibration exposure.

A comparison of hand-arm vibration syndrome between Malaysian and Japanese workers.

OBJECTIVES: The aim of this study was to investigate the clinical characteristics of HAVS in a tropical environment in comparison with a temperate environment. METHODS: We conducted a series medical examinations among the forestry, construction and automobile industry workers in Malaysia adopting the compulsory medical examination procedure used by Wakayama Medical University for Japanese vibratory tools workers. We matched the duration of vibration exposure and compared our results against the Japanese workers. We also compared the results of the Malaysian tree fellers against a group of symptomatic Japanese tree fellers diagnosed with HAVS. RESULTS: Malaysian subjects reported a similar prevalence of finger tingling, numbness and dullness (Malaysian=25.0%, Japanese=21.5%, p=0.444) but had a lower finger skin temperature (FST) and higher vibrotactile perception threshold (VPT) values as compared with the Japanese workers. No white finger was reported in Malaysian subjects. The FST and VPT of the Malaysian tree fellers were at least as bad as the Japanese tree fellers despite a shorter duration (mean difference=20.12 years, 95%CI=14.50, 25.40) of vibration exposure. CONCLUSIONS: Although the vascular disorder does not manifest clinically in the tropical environment, the severity of HAVS can be as bad as in the temperate environment with predominantly neurological disorder. Hence, it is essential to formulate national legislation for the control of the occupational vibration exposure.

Dose-response relationship between hand-transmitted vibration and hand-arm vibration syndrome in a tropical environment.

OBJECTIVES: The dose-response relationship for hand-transmitted vibration has been investigated extensively in temperate environments. Since the clinical features of hand-arm vibration syndrome (HAVS) differ between the temperate and tropical environment, we conducted this study to investigate the dose-response relationship of HAVS in a tropical environment. METHODS: A total of 173 male construction, forestry and automobile manufacturing plant workers in Malaysia were recruited into this study between August 2011 and 2012. The participants were interviewed for history of vibration exposure and HAVS symptoms, followed by hand functions evaluation and vibration measurement. Three types of vibration doses-lifetime vibration dose (LVD), total operating time (TOT) and cumulative exposure index (CEI)-were calculated and its log values were regressed against the symptoms of HAVS. The correlation between each vibration exposure dose and the hand function evaluation results was obtained. RESULTS: The adjusted prevalence ratio for finger tingling and numbness was 3.34 (95% CI 1.27 to 8.98) for subjects with lnLVD≥20 ln m(2) s(-4) against those <16 ln m(2) s(-4). Similar dose-response pattern was found for CEI but not for TOT. No subject reported white finger. The prevalence of finger coldness did not increase with any of the vibration doses. Vibrotactile perception thresholds correlated moderately with lnLVD and lnCEI. CONCLUSIONS: The dose-response relationship of HAVS in a tropical environment is valid for finger tingling and numbness. The LVD and CEI are more useful than TOT when evaluating the dose-response pattern of a heterogeneous group of vibratory tools workers.

Health risk evaluation of whole-body vibration by ISO 2631-5 and ISO 2631-1 for operators of agricultural tractors and recreational vehicles.

This paper presents experimental research evaluation of the vibration exposure for the health risk prediction during vehicle operation. The vibration measurements were carried out on a recreational vehicle and two types of agricultural tractors. The vibration levels were measured for different surfaces and vehicle speed conditions. Based on the analysis of the results in the small agricultural tractor operated in the workplace (frameworks), Sed exceeded 0.80 MPa by ISO2631-5:2004, and Av exceeded 0.89 m/s(2) by ISO2631-1:1997. That means that operators driving small agricultural tractors more than 8 h a day have a high probability of adverse health effects. However, the exposure value for the recreational vehicle had Sed < 0.5 MPa by ISO2631-5:2004 and Av < 0.5 m/s(2) by ISO2631-1:1997 on highways and local roads. That means Recreational Vehicle operators driving more than 8 h a day, have a low probability of adverse health effects. Also, for the recreational vehicle, vibration was taken at different speeds (40-60 km/h, 80 km/h, 100-120 km/h). However, the speed change did not appear to affect the vibration dose variation while driving a vehicle on the highway and road. Finally, the health effect index of ISO2631-5:2004 are almost the same as assessment of health effect by ISO2631-1:1997.

The clinical features of hand-arm vibration syndrome in a warm environment--a review of the literature.

UNLABELLED: 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 characteristics of vibrotactile perception threshold among shipyard workers in a tropical environment.

The objectives of this study are to determine the prevalence of hand-arm vibration syndrome (HAVS) and the characteristics of the vibrotactile perception threshold (VPT) among users of hand-held vibrating tools working in a tropical environment. A cross sectional study was done among 47 shipyard workers using instruments and a questionnaire to determine HAVS related symptoms. The vibration acceleration magnitude was determined using a Human Vibration Meter (Maestro). A P8 Pallesthesiometer (EMSON-MAT, Poland) was used to determine the VPT of index and little finger at frequencies of 31.5 Hz and 125 Hz. The mean reference threshold shift was determined from the reference threshold shift derived from the VPT value. The results show a moderate prevalence of HAVS (49%) among the shipyard workers. They were exposed to the same high intensity level of HAVS (mean = 4.19 ± 1.94 m/s(2)) from the use of vibrating hand-held tools. The VPT values were found to be higher for both fingers and both frequencies (index, 31.5 Hz = 110.91 ± 7.36 dB, 125 Hz = 117.0 ± 10.25 dB; little, 31.5 Hz = 110.70 ± 6.75 dB, 125 Hz = 117.71 ± 10.25 dB) compared to the normal healthy population with a mean threshold shift of between 9.20 to 10.61 decibels. The frequency of 31.5 Hz had a higher percentage of positive mean reference threshold shift (index finger=93.6%, little finger=100%) compared to 125 Hz (index finger=85.1%, little finger=78.7%). In conclusion, the prevalence of HAVS was lower than those working in a cold environment; however, all workers had a higher mean VPT value compared to the normal population with all those reported as having HAVS showing a positive mean reference threshold shift of VPT value.

Gender difference in subjective response to whole-body vibration under standing posture.

PURPOSE: The aim of this study was to examine whether there exist gender differences in subjective response to whole-body vibration (WBV) under standing posture. METHODS: Totally twenty-four participants (twelve males and twelve females) rated the discomfort of the test stimuli. The test stimuli included fore-and-aft (x), lateral (y), and vertical (z) vibration of three intensity levels (0.2, 0.4, and 0.8 m/s(2) r.m.s., unweighted), each of which had a constant power spectrum density at frequencies ranging from 1.0 to 20 Hz. The order of the test stimuli was fully randomized, and each stimulus was repeated three times. Subjective scale for discomfort caused by whole-body vibration exposure was obtained for each direction by using the category judgment method. Also, the mean Stevens' power law exponent was obtained for females and males at each vibration direction. RESULTS: The power exponents for females were significantly higher than those for males under fore-and-aft and lateral WBV exposure. Subjective discomfort scales obtained under fore-and-aft and lateral vibration exposure exhibited significant gender differences: the upper limits of categories up to "4: uncomfortable" for females were observed to be higher than those for males while the upper limits of category "5: very uncomfortable" for females were lower than those for males. In contrast, no significant gender differences were observed in the subjective discomfort scale or in the power law exponent for vertical WBV exposure. CONCLUSIONS: Our results suggest that females are subjectively more sensitive than males for fore-and-aft and lateral WBV exposure, especially at higher vibration magnitude. Therefore, the differential effects in subjective responses to WBV in females and males should be taken into account in the ISO standard currently used in discomfort evaluation.

Subjective ratings of whole-body vibration for single- and multi-axis motion.

Real-world whole-body vibration exposures comprise motion in fore-aft, lateral, and vertical directions simultaneously. There can also be components of roll, pitch, and yaw. If evaluating vibration with respect to human response, most investigators will use methods defined in ISO 2631-1. This uses frequency weightings that were originally derived from laboratory studies of the subjective responses to vibration in one direction at a time. This paper describes experiments that were carried out using a 6 degree-of-freedom vibration simulator to validate the applicability of ISO 2631-1 in multi-axis environments. Fifteen subjects were exposed to 87 stimuli comprising single-axis, dual-axis, and tri-axial random vibration, to which they were required to produce subjective ratings. It is shown that in this study the root-sum-of-squares method of summation of subjective ratings in individual axes was an adequate technique for prediction of subjective rating of multi-axis vibration. Better agreement between objective and subjective measures of vibration was obtained for unweighted vibration than for frequency weighted signals. The best agreement for this study was achieved when axis multiplying factors were set at 2.2 and 2.4 for x- and y-axis vibration, respectively. Different values could be appropriate for other postures, seats, and vibration conditions and should be determined in future studies.

Apparent mass and seat-to-head transmissibility responses of seated occupants under single and dual axis horizontal vibration.

The apparent mass and seat-to-head-transmissibility response functions of the seated human body are investigated under exposures to fore-aft (x), lateral (y), and combined fore-aft and lateral (x and y) axis whole-body vibration. The experiments were performed to study the effects of hands support, back support and vibration magnitude on the body interactions with the seat pan and the backrest, characterised in terms of fore-aft and lateral apparent masses and the vibration transmitted to the head under single and dual-axis horizontal vibration. The data were acquired with 9 subjects exposed to two different magnitudes of vibration applied along the individual x- and y- axis (0.25 and 0.4 m/s(2) rms), and along both the-axis (0.28 and 0.4 m/s(2) rms) in the 0.5 to 20 Hz frequency range, and analyzed to derive the biodynamic responses. A method was further derived to obtain total seated body apparent mass response from those measured at the backrest and the seatpan. The results revealed coupled effects of hands and back support conditions on the responses, while the vibration magnitude effect was relatively small. For a given postural condition, the biodynamic responses to dual-axis vibration could be estimated from the direct- and cross-axis responses to single-axis vibration, suggesting weakly nonlinear behaviour.

Determination of backrest inclination based on biodynamic response study for prevention of low back pain.

Whole-body vibration experiments with subjects under vertical vibration were performed to examine and evaluate effects of backrest inclination on vibration transmitted through seats to the human body by using biodynamic response parameters represented by apparent mass (APMS) and vibration power absorption (VPA). The biodynamic response parameters of twelve male subjects, exposed to vertical random vibration at 0.8 m/s(2) r.m.s., were characterized under three different backrest support conditions, with the upper body supported against backrest inclined at angles of 0 degrees (vertical), 10 degrees, and 30 degrees with respect to the vertical axis. An increased backrest inclination angle resulted in reduction of the total power absorption calculated particularly the frequency range of 1-20 Hz. Normalized APMS magnitudes showed a principal resonance at about 5 Hz for each subject for a backrest supported vertically. A second resonant peak appeared at about 7.5 Hz in addition to the primary resonant peak for a backrest inclined at an angle of 10 degrees and then became much steeper for a backrest inclined at angle of 30 degrees. For a backrest inclined at an angle of 30 degrees, the resonant peak at 5 Hz was less apparent than in other backrest inclination postures. All subjects showed the second resonant peak at about 7.5 Hz in the double-normalized VPA for a backrest inclined at an angle of 30 degrees. According to the evaluation of vibration absorption behavior performed in this study, backrest inclination angle is preferable between 10 degrees and 30 degrees from the viewpoint of prevention of low back pain disorder.

Establishment of one-axis vibration test system for measurement of biodynamic response of human hand-arm system.

Prolonged exposure to hand-arm vibration (HAV) due to use of hand-held power tools leads to an increased occurrence of symptoms of disorders in the vascular, neurological, and osteo-articular systems of the upper limbs called hand-arm vibration syndrome (HAVS). Biodynamic responses of the hand-arm system to vibration can be suggestive parameters that give us better assessment of exposure to HAV and fundamental data for design of low-vibration-exposure power tools. Recently, a single axis hand-arm vibration system has been installed in the Japan National Institute of Occupational Safety and Health (NIOSH). The aims of this study were to obtain the fundamental dynamic characteristics of an instrumented handle and to validate the performance and measurement accuracy of the system applied to dynamic response measurement. A pseudo-random vibration signal with a frequency range of 5-1,250 Hz and a power spectrum density of 1.0 (m/s2)2/Hz was used in this study. First the dynamic response of the instrumented handle without any weight was measured. After this measurement, the dynamic response measurement of the handle with weights mounted on the handle was performed. The apparent mass of a weight itself was obtained by using the mass cancellation method. The mass of the measuring cap on the instrumented handle was well compensated by using the mass cancellation method. Based on the 10% error tolerance, this handle can reliably measure the dynamic response represented by an apparent mass with a minimum weight of 2.0 g in a frequency range of 10.0 to 1,000 Hz. A marked increase in the AM magnitude of the weights of 15 g and 20 g in frequency ranges greater than 800 Hz is attributed not to the fundamental resonance frequency of the handle with weights, but to the fixation of the weight to the measuring cap. In this aspect, the peak of the AM magnitude can be reduced and hence should not be an obstacle to the biodynamic response measurement of the human hand-arm system. On the basis of the results obtained in this study, we conclude that this hand-arm vibration test system can be used to measure biodynamic response parameters of the human hand-arm system.

Vibration-isolating performance of cotton work gloves based on newly issued JIS T8114.

The mean vibration transmissibility values were measured for cotton work gloves commonly used in vibration-generating workplaces to evaluate the vibration isolating performance of cotton work gloves. The mean vibration transmissibility values of work cotton gloves were compared with those of four types of anti-vibration gloves measured in the same way. All the measurements were performed based on the newly issued JIS T8114 that is identical to ISO10819. Also, linear transmissibility values were calculated from the measured data. Cotton work glove samples did not satisfy the requirements specified in JIS T8114. All the test samples showed mean vibration transmissibility values of more than 1.0 for spectra M and H. In contrast, all the anti-vibration gloves tested in this study satisfied the JIS T8114 requirements. The linear transmissibility values of cotton work gloves were consistently higher than those of anti-vibration gloves for spectrum H. The linear transmissibility values of cotton work gloves were steady at about 0.9 up to 200 Hz, then increased with vibration frequency to about 1.0 at 400 Hz. In contrast, the linear transmissibility values of anti-vibration gloves increased with frequency to 1.0 at 30 Hz and then decreased with small peaks at 100 Hz and 300 Hz. Our results suggest that cotton work gloves do not show enough vibration-isolating performance. Therefore, attention should be paid to encouraging the widespread use of anti-vibration gloves in place of cotton work gloves to reduce exposure to hand-arm vibration.

Subjective scaling of hand-arm vibration.

The purpose of this research was to establish a scale for comfort with regard to hand-arm vibration using the category judgment method and to validate the frequency-weighting method of the ISO 5349-1 standard. Experiments were conducted using random signals as stimuli. These stimuli consisted of three types of signal, namely designated stimulus F, with flat power spectrum density (PSD) ranging from 1 to 1,000 Hz, stimulus H with PSD which became 20 dB higher at 1,000 Hz than at 1 Hz, and stimulus L that had a PSD 20 dB lower at 1,000 Hz. These stimuli were selected from the specific spectrum patterns of hand-held vibration tools. These signals were modified by the Wh frequency weighting in accordance with ISO 5349-1, and the R.M.S. values were adjusted to be equal. In addition, the signal levels were varied over a range of five steps to create 15 kinds of individual stimuli. The subjects sat in front of a vibrator and grasped the mounted handle which exposed them to vertical vibrations after which they were asked to choose a numerical category to best indicate their perceived level of comfort (or otherwise) during each stimulus. From the experimental results of the category judgment method, the relationship between the psychological values and the frequency-weighted R.M.S. acceleration according to the ISO 5349-1 standard was obtained. It was found that the subjective response scaling of hand-arm vibration can be used for design-objective values of hand-held tool vibration.

A pilot study of gene expression analysis in workers with hand-arm vibration syndrome.

The purpose of this pilot study was to examine differences in gene expressions by cDNA microarray analysis of hand-arm vibration syndrome (HAVS) patients. Vein blood samples were collected and total RNA was extracted. All blood samples were obtained in the morning in one visit after a standard light breakfast. We performed microarray analysis with the labeled cDNA prepared by reverse transcription from RNA samples, using the Human CHIP version 1 (DNA Chip Research Inc, Yokohama, Japan). There are 2,976 genes on the chip, and these genes were selected from a cDNA library prepared with human peripheral white blood cells (WBC). Different gene levels between the HAVS patients and controls, and between groups of HAVS with different levels of symptoms, were indicated by the randomized variance model. The most up-regulated genes were analyzed for their possible functions and association with the occurrence of HAVS. From the results of this pilot study, although the results were obtained a limited number of subjects, it would appear that cDNA microarray analysis of HAVS patients has potential as a new objective method of HAVS diagnosis. Further research is needed to examine the gene expression with increased numbers of patients at different stages of HAVS.

The apparent mass of the seated human exposed to single-axis and multi-axis whole-body vibration.

Most workplaces where workers are exposed to whole-body vibration involves simultaneous motion in the fore-and-aft (x-), lateral (y-) and vertical (z-) directions. Previous studies reporting the biomechanical response of people exposed to vibration have almost always used single-axis vibration stimuli. This paper reports a study where apparent masses of 15 subjects were measured whilst exposed to single-axis and tri-axial whole-body vibration. Each subject was exposed to 28 vibration conditions comprising every combination of single-axis and tri-axial vibration with magnitudes of 0.4 and 0.8 ms(-2) r.m.s. in each direction, once with backrest contact and once without backrest contact. Results show that increasing the magnitude of vibration in directions orthogonal to that being measured affects the apparent mass, causing a reduction in the resonance frequency as the total magnitude of vibration increases. It is demonstrated that the apparent mass resonance frequency is a function of the total vibration magnitude in all axes rather than a function of the vibration magnitude in the direction being measured. It is also shown that, for individuals, the frequency of the peak in the apparent mass in one direction is not related to the frequency of the peak in another direction. It is concluded that more complex biomechanical models are required in order to simulate human response to multi-axis vibration.

Necessary research for standardization of subjective scaling of whole-body vibration.

Researches into the relationship between the physical quantity of vibration and the subjectively perceived quantity become important in designs for the vibration environment. Subjective experimental methods to obtain the relationship between the physical quantity of vibration and the subjectively perceived quantity are different depending on the design objectives which consider the human sense of vibration characteristic. In this review, the following are outlined: (i) fundamental methods for obtaining the design objectives for vibration environments; (ii) reported findings on the physical quantity of vibration environments and the human characteristics of sense vibration; and (iii) problems with and limits of the ISO 2631-1 standard, which defines the subjective response of the ride comfort in public transportation. Finally, the directions of research into the subjective experimental methods for obtaining design objectives in the vibration environment considering of the human characteristics of sense vibration are described.

Effect of backrest and torso twist on the apparent mass of the seated body exposed to vertical vibration.

Occupational exposure to whole-body vibration is often combined with a requirement to perform twisting actions. This paper reports a study where the effect of twisting on the biomechanical response of the seated person was investigated. Twelve male subjects were exposed to vertical random whole-body vibration at 0.4 m/s2 r.m.s. Each subject sat in four different postures: 'back-on', 'back-off', 'twist' (where subjects were required to twist the torso by 90 degrees) and 'move' (where subjects were required to performing a moving task with extended arms). Similar apparent masses were measured for the 'back-on', 'back-off' and 'twist' conditions, where a peak occurred at about 6 Hz. For the 'move' condition, the peak in the apparent mass was attenuated indicating a different biomechanical response in this posture. The 6 Hz peak in fore-and-aft cross-axis apparent mass was eliminated in the 'move' condition. It is suggested that the change in biomechanical response is due to either the extended arms acting as a passive vibration absorber or that the twisting action interferes with the usual acceleration-muscle feedback system. Further work will be required to test these hypotheses.

Comparison of the apparent mass during exposure to whole-body vertical vibration between Japanese subjects and ISO 5982 standard.

OBJECTIVE: The purpose of this study was to investigate the apparent mass of the sitting human body and to compare it with current experimental data and the ISO 5982 standard impedance model. METHOD: The apparent mass of the seated human body in the vertical direction was measured. Twelve male subjects were exposed to random whole-body vibration of frequency range (1-20 Hz), with a vibration excitation level of 1.0 m/s2 r.m.s. The body posture was upright with no backrest contact. RESULTS: The obtained apparent masses were compared to the International Standard, (ISO 5982). The biodynamic response of the seated Japanese subjects peaked in the 4-6.5 Hz frequency range, which is little bit higher than the reported range of fundamental frequencies (4.5-5 Hz) in most other studies which used different experimental conditions. The outcomes show a clear difference between apparent mass of Japanese subjects and ISO 5982 data. CONCLUSION: It is not sufficient to apply the ISO 5982 standard to Japanese vehicle design or dummy design.