The influence of biodynamic factors on the mechanical impedance of the hand and arm

 The purpose of this study was to investigate the mechanical impedance of the human hand-arm system during exposure to random vibration under various experimental conditions and to evaluate statistically whether these experimental conditions have any influence on magnitude and phase of the mechanical impedance. A further aim was to compare the obtained results with other investigations where sinusoidal excitation has been used. The mechanical impedance was estimated in ten healthy subjects during exposure to random vibration, with a constant velocity spectrum within the frequency range 4–2000 Hz, by use of a specially designed laboratory handle. In the study, the influence of various conditions, such as vibration direction ( X_h, Y_h, Z_h), grip force (25–75 N), feed force (20–60 N), frequency-weighted acceleration level (3, 6, 9, 12 m/s²) and hand and arm posture (five flexions, two abductions) were studied. The outcome showed that the vibration direction and the frequency of the vibration stimuli have a strong significant influence on the impedance of the hand. An increased vibration level resulted in a significantly lower impedance for frequencies over 100 Hz. Increased grip and feed forces led on the other hand to an increased impedance for all frequencies. With regard to hand and arm posture, the results show that the flexion and abduction had a significant contribution for frequencies below 30 Hz. Furthermore, the influence of some of the studied variables had a non-linear effect on the impedance but also differed between different exposure directions. It was concluded, moreover, that the vibration response characteristics of the hand and arm differ, depending upon whether the signal is a discrete frequency signal or a signal consisting of several frequencies. Received: 2 August 1996/Accepted: 20 September 1996     

Acute effects of vibration from a chipping hammer and a grinder on the hand-arm system.

OBJECTIVES--The purpose of this study was to compare various effects on the hand-arm system of vibration exposure from a chipping hammer and a grinder with the same frequency weighted acceleration. Grip and push forces were measured and monitored during the exposure. The various effects were: muscle activity (measured with surface electrodes), discomfort ratings for different parts of the hand-arm system (made during and after exposure), and vibration perception threshold (for 10 minutes before and 10 minutes after the exposure). RESULTS--No increase in muscle activity due to exposure to vibration was found in the hand muscle studied. In the forearm, conversely, there was an increase in both muscle studied. For the upper arm the muscle activity only increased when exposed to impact vibration. Subjective ratings in the hand and shift in vibration perception threshold were effected more by the grinder than the hammer exposure. CONCLUSION--These results show that the reaction of the hand-arm system to vibration varies with frequency quantitatively as well as qualitatively. They do not support the notion that one single frequency weighted curve would be valid for the different health effects of hand-arm vibration (vascular, musculoskeletal, neurological, and psychophysiological).     

Mechanical impedance and absorbed power of hand-arm under x(h)-axis vibration and role of hand forces and posture

The biodynamic responses of the hand-arm system under x(h)-axis vibration are investigated in terms of the driving point mechanical impedance (DPMI) and absorbed power in a laboratory study. For this purpose, seven healthy male subjects are exposed to two levels of random vibration in the 8-1,000 Hz frequency range, using three instrumented cylindrical handles of different diameters (30, 40 and 50 mm), and different combinations of grip (10, 30 and 50 N) and push (0, 25 and 50 N) forces. The experiments involve grasping the handle while adopting two different postures, involving elbow flexion of 90 degrees and 180 degrees, with wrist in the neutral position for both postures. The analyses of the results revealed peak DPMI magnitude and absorbed power responses near 25 Hz and 150 Hz, for majority of the test conditions considered. The frequency corresponding to the peak response increased with increasing hand forces. Unlike the absorbed power, the DPMI response was mostly observed to be insensitive to variations in the excitation magnitude. The handle diameter revealed obvious effects on the DPMI magnitude, specifically at frequencies above 250 Hz, which was not evident in the absorbed power due to relatively low velocity at higher frequencies. The influence of hand forces was also evident on the DPMI magnitude response particularly at frequencies. above 100 Hz, while the effect of hand-arm posture on the DPMI magnitude was nearly negligible. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the excitation level over the entire frequency range, while the influence of hand-arm posture on the total absorbed power was observed to be important. The effect of variations in the hand forces on the absorbed power was relatively small for the bent elbow posture, while an increase in either the grip or the push force coupled with the extended arm posture resulted in considerably higher energy absorption. The results suggested that the handle size, hand-arm posture and hand forces, produce coupled effect on the biodynamic response of the hand-arm system.     

Measurements of the impedance of the hand and arm

Summary The mechanical impedance of the hand and arm was studied on ten healthy subjects during exposure to sinusoidal vibration within the frequency range of 2 to 1000 Hz. A special handle for the measurements was constructed. The influence of vibration direction, handle grip, grip force, vibration level, hand-arm posture and sex as well as anthropometric data were studied. The results show that the impedance of the hand-arm mainly depends on the frequency and direction of the vibration stimuli. Higher vibration levels, as well as more firm hand-grips, resulted in higher impedance. Furthermore, the outcome shows that experiments conducted with different hand-arm postures had an active influence on the mechanical impedance. Moreover, the subjects' sex and constitution of the hand and arm affected the impedance to a large extent.     

Transmission of vibration energy to different parts of the human hand-arm system

The aim of this study was to investigate the transmission of vibration energy to three selected points along the hand and arm (knuckle, wrist and elbow) and to compare the energy transmission for two different kinds of vibration exposures, i.e. random and sinusoidal. The transmission of vibration energy was estimated for ten subjects during exposure to random (within the frequency range 20–5000 Hz) and sinusoidal vibration at eight different frequencies (20, 40, 80, 160, 320, 630, 1250 and 1600 Hz). The random and sinusoidal vibrations had a frequency-weighted acceleration level of 3 m/s². The energy transmission was determined by simultaneous vibration measurements at the vibrating handle and in the hand-arm system. The measurements were made with a laser-velocity transducer and specially constructed equipment. The grip and feed forces were held constant at 40 N. The results show that the energy transmission decreases with the distance from the source. The results also show that the energy transmission is dependent on the frequency for the random vibration exposures. No clear frequency dependence of the energy transmission could be found for the sinusoidal vibrations. It may also be concluded that there are differences in the energy transmission due to types of exposure, sinusoidal vibration showing higher transmission of energy to the hand-arm system than random vibration, especially at higher frequencies. Received: 16 October 1996 / Accepted: 7 February 1997     

Vibration perception thresholds in workers exposed to vibration

Summary The vibration perception thresholds (VPT) at six frequencies from 16 to 500 Hz were examined in 77 workers exposed to hand-arm vibration and in 77 controls using a limits procedure. A dose-response relationship between VPTs and exposure to vibration was found, and the age-adjusted VPTs at each frequency were higher in workers exposed to vibration than in controls. Carpal tunnel syndrome (at 250 Hz) and consumption of alcohol (at 125 Hz) significantly increased the VPT, but vibration-induced white finger was not correlated with VPT. Indices for low (16 and 32 Hz) and high (63–500 Hz) VPT frequencies were calculated to evaluate the entire vibrogram, which consisted of several frequencies with two numbers. The results showed that hand-arm vibration disturbs first the high frequencies, and that the disturbance spreads thereafter to the low frequencies. The characteristics of the VPT test regarding vibration exposure and the association between VPT and nerve symptoms in the hand support the view that VPT is a useful measure for vibration-induced sensory nerve damage.     

Combined effects of hand-arm vibration and noise on temporary threshold shifts of hearing in healthy subjects

 Object: To investigate whether hand-arm vibration and noise have a combined effect on temporary threshold shift (TTS) of hearing among healthy subjects. Method and design: Nineteen healthy subjects with an average age of 25.7 (SD 7.7) years were exposed to vibration (30 m/s², 60 Hz), noise [90 dB(A)] and both, respectively. The subject’s right hand was placed on the plate of a vibrator and the right ear exposed to noise via headphones. Subjects were exposed to vibration and/or noise for 3 min and after a 1-min pause the exposure was repeated five times. Hearing thresholds at 1, 4 and 6 kHz were measured during the time periods before, between (during pauses) and after exposure. Results: Exposure to vibration alone caused almost no hearing threshold changes at every frequency tested. But exposure to noise or a combination of vibration and noise caused a significant increase in TTSs at 4 and 6 kHz. Moreover, exposure to a combination of vibration and noise caused significantly higher TTSs than exposure to noise at 4 and 6 kHz. Conclusion: The present results demonstrate the combined effects of hand-arm vibration and noise on hearing: simultaneous exposure to hand-arm vibration and noise can enhance the TTS of hearing more than noise exposure, though hand-arm vibration alone may hardly affect TTS. Received: 14 May 1996/Accepted: 20 September 1996     

Studies of combined effects of sinusoidal whole body vibrations and noise of varying bandwidths and intensities on TTS2 in men

Summary This study analyses the data from three laboratory experiments concerning the separate and combined effects on temporary threshold shifts in hearing (TTS2) of sinusoidal low-frequency (5 Hz — 2.12 m/s² and 10 Hz —2.65 m/s²), whole body vibration (along the Z-axis), and continuous (white) noise with eight different bandwidths and intensity levels of 85 dB(A), 90 dB(A) and 98 dB(A). Altogether 370 separate personal experiments were performed using a one-man exposure chamber system. A single experiment consisted of a 30-min pre-exposure period, three 16-min exposure periods, and a 15-min post-exposure period. The data suggested that the TTS₂ induced by noise was increased by vibration. Actually, vibration at a frequency of 5 Hz and noise with bandwidths of 1–4 kHz, 1–8 kHz or 0.2–16 kHz comprised the most significant exposure combinations. After such exposures, the increase in TTS₂ values was defined most clearly for 4 kHz and 6 kHz test frequencies. The increase of thresholds was most marked during the first 16-min exposure period, even though most TTS₂ values determined after the third consecutive exposure period were higher than after the first and second exposures. Figures obtained after the third exposure period proved that exposure to simultaneous vibration and broad band noise (i.e. noise with a bandwidth of 0.2–16 kHz) increased TTS₂ values 1.2–1.5 times more in the 4 kHz audio range than such a broad band noise alone. No single vibration condition induced the same amount of TTS₂.     

Autonomic and peripheral nervous system dysfunction in workers exposed to hand-arm vibration: a study of R-R interval variability and distribution of nerve conduction velocities

Summary To assess the effects of vibrating-tool operation on the autonomic and peripheral nervous system, we measured the variability in the electrocardiographic R-R interval (CV_RR) and the distribution of nerve conduction velocities (DCV) in 24 men who were vibrating-tool operators and in 17 healthy adult men (control group). Of the 24 tool operators, 13 had a history of vibration-induced white finger [VWF(+) group] and 11 had no such history [VWF(–) group]. Two components of CV_RR, i.e. C-CV_RSA and C-CV_MWSA, which have been considered to reflect parasympathetic and sympathetic activities, respectively, were also examined. Both the CV_RR and the C-CV_RSA in the VWF(+) group and the CV_RR in the VWF(–) group were found to be significantly depressed as compared with the control values; moreover, a significant difference in the C-CV_RSA was observed between the VWF(+) group and the VWF(–) group. The faster DCVs and the sensory median nerve conduction velocity were significantly slowed in the VWF (+) and VWF(–) groups. The C-CV_MWSA was significantly correlated with most of the DCV parameters and with the median nerve conduction velocities in all 24 vibrating-tool operators. These data suggest that operation of vibrating tools, which involves exposure to combined stressors of local vibration, heavy work, climate, and noise, affects both the faster myelinated nerve-fiber activity and the parasympathetic activity; the sympathetic activity at rest in workers exposed to hand-arm vibration may be related to depression of peripheral nerve conduction.     

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.     

Dose-response relation between exposure to two types of hand-arm vibration and sensorineural perception of vibration.

OBJECTIVES--31 railway workers and 32 lumberjacks were examined to compare the dose-response relation between the exposure to two types of hand-arm vibration and the sensory disturbances in peripheral nerves as evaluated by the vibration perception thresholds (VPTs). METHODS--Clinical examinations were carried out that included measurements of the VPTs, and electroneuromyography (ENMG), and an inquiry to confirm the use of vibrating tools. Diseases of the central nervous system and neuropathies were checked by inquiry and a clinical examination, diabetes was excluded by a blood sample analysis, and the subjects with carpal tunnel syndrome confirmed with ENMG were excluded from the study. RESULTS--Lifetime use of hand held tamping machines (railway workers) and chain saws (lumberjacks) had a significant correlation with the VPTs at frequencies from 32 to 500 Hz. The increase of the VPTs (250 Hz) in relation to use of vibrating tools was 1.8-fold higher on average in the whole group and 2.3-fold higher in the young (< 45) railway workers who had used hand held tamping machines, than in the corresponding groups of lumberjacks, who had used chain saws, whereas the frequency weighted acceleration of vibration in tamping machines was fourfold. CONCLUSION--There was a significant dose-response relation between the exposure to hand-arm vibration and the VPTs. The VPTs as a function of the frequency weighted acceleration of vibration and the exposure to vibration gave promising results for assessment of the risk of damage to sensory nerves induced by vibration.     

The Effects of Impact Vibration on Peripheral Blood Vessels and Nerves

Research regarding the risk of developing hand-arm vibration syndrome after exposure to impact vibration has produced conflicting results. This study used an established animal model of vibration-induced dysfunction to determine how exposure to impact vibration affects peripheral blood vessels and nerves. The tails of male rats were exposed to a single bout of impact vibration (15 min exposure, at a dominant frequency of 30 Hz and an unweighted acceleration of approximately 345 m/s²) generated by a riveting hammer. Responsiveness of the ventral tail artery to adrenoreceptor-mediated vasoconstriction and acetylcholine-mediated re-dilation was measured ex vivo. Ventral tail nerves and nerve endings in the skin were assessed using morphological and immunohistochemical techniques. Impact vibration did not alter vascular responsiveness to any factors or affect trunk nerves. However, 4 days following exposure there was an increase in protein-gene product (PGP) 9.5 staining around hair follicles. A single exposure to impact vibration, with the exposure characteristics described above, affects peripheral nerves but not blood vessels.     

Effects of sinusoidal whole-body vibration on the lumbar spine: the stress-strain relationship

Summary The aim of this experimental study was to estimate the strain in the lumbar spine due to whole-body vibration (WBV). Four male subjects were exposed to vertical sinusoidal WBV with frequencies ranging from 1 to 15 Hz at two intensities (I₁ = 1.5 ms^–2 rms; I₂ = 3.0 ms^–2 rms). The compressive forces acting on the disc L3-4 during the extreme values of acceleration were predicted on the basis of anthropometric data, EMG of back muscles and the acceleration of the upper trunk, using a simple biomechanical model. The estimated mechanical activity of back muscles was not able to protect the spine under many exposure conditions. The highest compressive forces were predicted for WBV with 7.5, 8 and 4.5 Hz. The results suggest the possibility of fatigue failures at the endplates of lumbar vertebrae after intense long-term exposure to WBV.The authors gratefully acknowledge the help and assistance of G. Menzel, R. Vizcaino, and A. Weissmüller     

Assessment of hand-arm vibration exposure among traffic police motorcyclists

 The aims of this study were (1) to evaluate subjective symptoms in the hand-arm system of all traffic police motorcyclists of a city located in the central part of Japan and (2) to assess their hand-arm vibration exposure associated with traffic police motorcycle riding. The study population consisted of 119 motorcycling traffic policemen and 49 male controls. By means of a questionnaire, information on the occupational history and the presence of subjective symptoms in the hand-arm system of all subjects was obtained. Vibration was measured on the handlebars of the representative motorcycles and on the hands of the riders. The 4- and 8-h energy-equivalent frequency-weighted acceleration as well as the lifetime vibration dose were calculated for all police motorcyclists. The prevalence of finger blanching in the traffic police motorcyclists was 4.2%, but none of the controls had this symptom. The rates of finger numbness (19.3%), finger stiffness (16.0%), shoulder pain (13.4%), and shoulder stiffness (45.4%) were significantly higher among police motorcyclists as compared with controls. The root-mean-square (rms) frequency-weighted acceleration on the handlebars of police motorcycles was in the range of 2.2–4.9 m/s² rms. The computed 4- and 8-h energy-equivalent frequency-weighted acceleration values were 2.8– 4.5 and 2.0 –3.2 m/s² rms, respectively. A pattern of increasing percentage prevalence with increasing cumulative vibration dose was noticed. The subjects with a lifetime vibration dose of more than 20.1 m² h ³ s^-4 (ln scale) showed significantly higher prevalence rates for symptoms in the fingers and shoulders as compared with the control group. As occupational vibration exposure of traffic police motorcyclists might be considered a risk factor for the development of symptoms in the hand-arm system of the riders, its evaluation and control is needed for prevention methodology evolution. Received: 15 April 1996/Accepted: 8 November 1996     

Acute effects of continuous and intermittent vibration on finger circulation

Objectives To compare the acute response of finger circulation to continuous and intermittent vibration having the same total duration of vibration exposure and the same energy-equivalent acceleration magnitude.Methods Finger blood flow (FBF) was measured in the middle and little fingers of both hands of ten healthy men. Finger skin temperature (FST) was measured in the middle right finger. With a static load of 10 N, the middle finger of the right hand was exposed to 125 Hz at 44 m s^–2 root mean square (r.m.s.) in five conditions: (1) 30 min continuous exposure, (2) two periods of 15 min, separated by a 15 min period with no vibration, (3) four periods of 7.5 min, separated by 7.5 min periods with no vibration, (4) eight periods of 3.75 min, separated by 3.75 min periods with no vibration, (5) 16 periods of 1.88 min, separated by 1.88 min periods with no vibration. All five exposures correspond to an 8 h energy-equivalent frequency-weighted acceleration magnitude of 1.4 m s^–2 r.m.s. according to International Standard ISO 5349–1 (2001). Finger circulation was measured in all four digits before the application of vibration and at fixed intervals during vibration exposure and during a 45 min recovery period.Results The FST did not change during vibration exposure, whereas all vibration conditions produced significant reductions in FBF of the vibrated finger when compared with the pre-exposure FBF. During vibration exposure, the vibration caused a similar degree of vasoconstriction in the vibrated finger without evidence of cumulative effects during intermittent exposure. After the end of exposure to 30 min of continuous vibration there was a progressive decrease in the FBF, whereas there was no statistically significant reduction following exposure to intermittent vibration.Conclusions For the vibration stimuli investigated (exposure durations varying from 1.88 min to 30 min, with rest periods varying from 1.88 min to 15 min), the reduction of FBF during exposure was the same for continuous and intermittent vibration. The after effect of vibration was greater following the continuous vibration exposure. Although some evidence from this study is consistent with the notion that intermittent vibration has a less severe effect than continuous vibration, this evidence is not yet conclusive.     

Bioresponses in men after repeated exposures to single and simultaneous sinusoidal or stochastic whole body vibrations of varying bandwidths and noise

Summary This study deals with the changes in temporary hearing threshold (TTS₂), upright body posture sway amplitudes in the X and Y direction, heart rate (HR), R-wave amplitude (RWA), systolic (SBP) and diastolic (DBP) blood pressure, pulse pressure (PP) and the index characterizing haemodynamic activity (HDI), when the subjects were exposed to noise alone, to vibrations alone or to simultaneous noise and vibrations. The experiments were carried out in an exposure chamber and the number of exposure combinations was 12. Seven healthy, male students volunteered as subjects, making a total number of 84 experiments. For each person the experiment consisted of a 30-min control period, five consecutive 16-min exposures, between which there was a 4-min measuring interval, and a 15-min recovery period. The noise was broadband (bandwidth 0.2–16.0 kHz) A-weighted (white) noise. The noise categories were: (1) no noise and (2) noise with an intensity of 90 dBA. The categories of low-frequency whole body vibration in the direction of the Z-axis were: (1) vibration within the range 4.4–5.6 Hz, (2) vibration within the range 2.8–5.6 Hz, (3) vibration within the range 2.8–11.2 Hz, (4) vibration within the range 1.4–11.2 Hz and (5) sinusoidal vibration with a frequency of 5 Hz. The (rms) acceleration in all the vibration models was 2.12 m/s². The results showed that the (TTS₂), values at 4 and 6 kHz increased as a result of simultaneous exposure to noise and vibration significantly more than as a result of exposure to noise alone. The (TTS₂), values increased more intensely during the first 16-min exposure. The means of the variances in the amplitudes of body upright posture sway changed not only after exposures to vibration alone, but also after exposure to noise alone. The means of the sway variances in the X and Y directions at 0.1 Hz and within the range 0.06 to 2.00 Hz increased only when the vibration in the noise-vibration combination was sinusoidal. The changes in the heart rate, R-wave amplitude and blood pressure values also depended on the bandwidth of the vibration, the number of consecutive exposures and on whether the subjects were simultaneously exposed to noise in addition to vibration. As a rule, the effects of sinusoidal vibration differed from those due to stochastic vibrations.Some preliminary results from measurements were presented in Moscow at the International Working Meeting Criteria of evaluation of the effects of whole-body vibration on a man, 12–16 March, 1984.     

Different acute effects of single-axis and multi-axis hand-arm vibration

Under laboratory conditions the effects of single-axis and multi-axis hand-arm vibration exposure on several strain parameters were tested in up to 20 male subjects. As parameters of these acute effects, the biodynamic vibration behavior of the hand-arm system, the electrical activity of the most affected muscle groups, the skin temperature, the vibration sensitivity of the fingertips, and the subjective vibration sensation were measured. When comparing simulated three-axis vibration exposure with single-axis vibration exposure, synergistic effects in the form of an increasing reaction could be found. It could be proven that the vector sum of the frequency-weighted acceleration in the three axes represents the acute effects better than does the weighted acceleration in the main axis alone. This summation has to take into account the relatively lower effects of vibration in the x- or y-direction compared with the z-direction. On the basis of the experimental results a new proposal for frequency weighting of the three different axes and an energetic summation procedure are derived. Application of this knowledge in the International Standard ISO 5349 is proposed.     

Response of finger circulation to energy equivalent combinations of magnitude and duration of vibration

OBJECTIVES—To investigate the acute response of finger circulation to vibration with different combinations of magnitude and duration but with the same "energy equivalent" acceleration magnitude according to current standards for hand transmitted vibration.
METHODS—Finger skin temperature (FST) and finger blood flow (FBF) were measured in the middle fingers of both hands of 10 healthy men who had not used hand held vibrating tools regularly. With a static load of 10 N, the right hand was exposed to 125 Hz vibration with the following unweighted root mean square (rms) acceleration magnitudes and durations of exposure: 44 m/s² for 30 minutes; 62 m/s² for 15 minutes; 88 m/s² for 7.5 minutes; 125 m/s² for 3.75 minutes; and 176 m/s² for 1.88 minutes. These vibration exposures produce the same 8 hour energy equivalent frequency weighted acceleration magnitude (~1.4 m/s² rms) according to international standard ISO 5349 (1986). Finger circulation was measured in both the right (vibrated) and the left (non-vibrated) middle fingers before application of the vibration, and at fixed intervals during exposure to vibration and during a 45 minute recovery period.
RESULTS—The FST did not change during exposure to vibration, whereas vibration with any combination of acceleration magnitude and duration produced significant percentage reductions in the FBF of the vibrated finger compared with the FBF before exposure (from −40.1% (95% confidence interval (95% CI) −24.3% to −57.2%) to −61.4% (95% CI −45.0% to −77.8%). The reduction in FBF during vibration was stronger in the vibrated finger than in the non-vibrated finger. Across the five experimental conditions, the various vibration stimuli caused a similar degree of vasoconstriction in the vibrated finger during exposure to vibration. There was a progressive decrease in the FBF of both fingers after the end of exposure to vibration with acceleration magnitudes of 44 m/s² for 30 minutes and 62 m/s² for 15 minutes. Significant vasoconstrictor after effects were not found in either finger after exposure to any of the other vibration stimuli with greater acceleration magnitudes for shorter durations.
CONCLUSIONS—For the range of vibration magnitudes investigated (44 to 176 m/s² rms unweighted; 5.5 to 22 m/s² rms when frequency weighted according to ISO 5349), the vasoconstriction during exposure to 125 Hz vibration was independent of vibration magnitude. The after effect of vibration was different for stimuli with the same energy equivalent acceleration, with greater effects after longer durations of exposure. The energy equivalent acceleration therefore failed to predict the acute effects of vibration both during and after exposure to vibration. Both central and local vasoregulatory mechanisms are likely to be involved in the response of finger circulation to acute exposures to 125 Hz vibration.


Keywords: finger circulation; energy equivalent acceleration magnitude; vibration frequency; magnitude; and duration     

Recent advances in biodynamics of human hand-arm system

The biodynamics of human hand-arm system is one of the most important foundations for the measurement, evaluation, and risk assessment of hand-transmitted vibration (HTV) exposure. This paper presents a new conceptual model relating factors influencing cause-effect relationships for HTV exposure, a new study strategy, and a comprehensive review of the recent advances in the biodynamics closely associated with HTV exposure. The review covers the following five aspects: theoretical modeling of biodynamic responses, vibration transmissibility, driving-point biodynamic responses, evaluation of anti-vibration gloves, and applied forces. This review finds that some significant advances in each of these aspects have been achieved in the recent years. Several important issues and problems in the biodynamic measurement have been identified and resolved, which has significantly helped improve the reliability and accuracy of the experimental data. The results reported in recent years suggest that, from the point of view of biodynamics, the frequency weighting specified in ISO 5349-1 (2001) overestimates the low frequency effect but underestimates the high frequency effect on the fingers and hand. The major problems, issues, and topics for further studies are also outlined in this paper. It is anticipated that the further studies of the biodynamics of the system will eventually lead to establishment of a robust vibration exposure theory. Although this review focuses on the biodynamics of the hand-arm system, the fundamental concepts and some methodologies reviewed in this paper may also be applicable for the study of whole-body vibration exposure.     

Effects of combined hand-arm vibration and cold on skin temperature

Summary Under laboratory conditions 14 healthy male subjects were exposed to hand-arm vibration (a_hzw = 6.3 m/s²) at different air temperatures (5°, 12°, 18° and 25°C). Static load (grip force 15 N, push force 40 N) was kept constant. Finger tip temperature as an indirect criterion of the peripheral blood circulation was measured. As expected, low air temperatures (5°, 12° and 18°C) cause a strong decrease of skin temperature. Under additional stress of vibration connected with static load, a further decrease of the mean skin temperature was noted. At this, static load proved to have a predominant influence on the acute diminution of skin temperature. The individual reaction to the stressors varied considerably. Field tests during practical work with a chain saw at low air temperatures showed results similar to those of the laboratory tests. The protective effect of a grip heating system could be demonstrated.Paper presented at the United Kindom and French joint meeting on Human Response to Vibration, 26–28 September 1988, INRS, Vandeuvre, France