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A vibrotactile test for assessing the presence or absence of sensory symptoms in the hand has been developed from thresholds believed mediated by Merkel disks and Meissner corpuscles at the fingertips. It is constructed from the summed differences between the thresholds recorded at the fingertip of an individual and the mean values of the threshold for healthy persons at the same stimulation frequencies. The summed normalized threshold shift, TS(Sum(SD)), is shown to be related to reports by subjects of numbness and pain using three statistical tests for evaluating the significance of associations in 2x2 contingency tables. The small number of subjects (15) restricts direct calculation of a fence value for TS(Sum(SD)), t, between the presence and absence of symptoms: accordingly, interpolation between calculated t values has been performed graphically. A common range of t values can be identified that is judged significantly by each statistical test (3.3

Two tools for assessing tactile sensory disturbances in the hands have been constructed from mechanoreceptor-specific vibrotactile threshold shifts, and thresholds changes with time, and employed in a prospective study of forest workers (N=18). Statistically significant positive threshold shifts (i.e., reductions in sensitivity compared to the hands of healthy persons) were found in five hands at study inception (13.9%), and 15 hands at follow-up (41.7%). Four patterns of threshold shift could be identified, involving selectively the median and/or ulnar nerve pathways and/or end organs. Statistically significant positive threshold changes (i.e., reductions in sensitivity with time) were recorded in 69.4% of the hands over a five-year period, even though a majority of the workers remained symptom free. If the thresholds recorded from subjects not working with power tools are used to control for aging, lifestyle, and environmental factors during the five year period, then 40% of the remaining subjects are found to be experiencing work-related threshold changes in their hands. The ability of the threshold shift metric to predict the numbness reported by these subjects shows that it is closely associated with the tactile sensory changes occurring in their hands.

Hypothesis: The sensorineural hearing loss (HL) after middle ear surgery has been explained by the noise generated by drilling, without considering the vibration generated by the burr., Background: The role of temporal bone vibration in the etiology of the HL was evaluated., Methods: An electromagnetic shaker was used to vibrate the bony external ear canal of guinea pigs at different frequencies ranging from 32 to 1,000 Hz and at intensities ranging from 4.2 to 18.8 m/s for 15 minutes. The hearing threshold was measured with auditory evoked responses. A total of 30 animals were tested., Results: After vibration, 60% of the guinea pigs developed a threshold shift (TS) exceeding 10 dB at two frequencies, with average TS of 8.8 dB across all frequencies and animals. The exposure to vibration at higher frequencies (range, 500-1,000 Hz) produced stronger TS than did the exposure to lower frequencies (range, 32-250 Hz). The vibration-induced TS showed prominent recovery so that after 7 days, TS was 2.4 dB on average and 27 of 30 animals had recovered. After 14 days, the TS was 1.3 dB. The vibration excitation measurements showed that at lower frequencies, the vibration transmission into the skull was significantly greater than at higher frequencies, at which the transmission was heavily attenuated. There were no acoustic resonances detected in the skull. The frequency of vibration and the hearing frequency in auditory brainstem response were significant determinants in the model explaining the vulnerability of vibration on hearing. Hearing loss primarily occurred at higher frequencies. The HL was mostly reversible, consistent with the results observed after human temporal bone surgery., Conclusion: We conclude that in the guinea pig model, the temporal bone vibration at higher frequencies produced a more severe HL than did the vibration at lower frequencies, although the vibration at higher frequencies caused less efficient transmission from the vibrating probe to the temporal bone. The guinea pig model may be useful in the development of surgical techniques and in the understanding of temporal bone pathology.

Two metrics, expressing the change in mechanoreceptor-specific vibrotactile thresholds at a fingertip over a time interval of months or years, and the shift in threshold from the mean values recorded from the fingertips of healthy persons, have been constructed for thresholds measured from individual fingers. The metrics assume the applicability of the acute adaptation property of mechanoreceptors, which has been confirmed by thresholds obtained from 18 forest workers on two occasions, separated by 5 years. Hence, when expressed in decibels, both threshold changes and threshold shifts may be averaged at frequencies mediated by the same receptor population to improve precision. Differences between threshold changes at frequencies mediated by the same receptor population may be used to identify inconsistent subject performance, and hence potentially erroneous results. For this group of subjects, the threshold changes and threshold shifts at frequencies believed mediated by the slowly adapting type I (SAI) (4 and 6.3 Hz) and rapidly adapting type I (FAI) (20 and 32 Hz) receptors within each finger were correlated. In these circumstances, which may be expected to occur for some work-induced and systemic peripheral neuropathies, both threshold changes and threshold shifts may be summed over SAI and FAI receptors to improve precision, and hence the potential for interpretation.

Transcranial vibration was applied for seven animals at a frequency of 250 Hz for 15 min, and five animals were used as normal controls to investigate cellular and molecular mechanism linked to vibration-induced hearing loss in animal model. Compound action potential (CAP) thresholds were measured by round window niche electrode. The expression of tumour necrosis factor alpha (TNF-alpha) and its receptors (TNF R1, TNF R2), vascular endothelium growth factor (VEGF) and its receptors (VEGF R1, VEGF R2) were analysed by immunohistochemistry. Transcranial vibration caused expression of TNF-alpha, TNF R1 and TNF R2 in the cochlea and the expression of TNF R2 was stronger than that of TNF R1. Vibration also induced VEGF and VEGF R2 expression in the cochlea. The average immediate hearing loss was 62 dB and after three days still 48 dB. It is concluded that transcranial vibration as during temporal bone drilling produces cochlear shear stress that is connected with up-regulation of TNF-alpha and its receptors. Also VEGF and VEGF R2 are up-regulated. These responses may be linked to both the damage and repair process of the cochlea.

Sensorineural hearing loss following a variety of acoustic trauma, including middle ear surgery, is well known. Current literature, which points to the deleterious influence of noise on the inner ear during surgery, has yet to assess the influence of vibration generated by the burr. The purpose of the study reported here was to establish an animal model that mimics drilling and can be used to explore methods of hearing loss prevention and treatment. A specially developed electromagnetic vibrator was calibrated and used in 59 guinea pigs to induce hearing loss. Both young and old guinea pigs were used. The bony external ear canal of guinea pigs were exposed to vibration or sound of varying duration and intensity. The vibration of the temporal bone and noise level in the middle ear were measured. Electrocochleography was recorded to evaluate the hearing loss. Among the young animals, 90% developed a significant threshold shift (TS > 20 dB), when vibrated with 250 Hz at an intensity of 6.2 m/s2 for 15 min. An average of 42 dB TS was observed. With 10 min exposure 63% showed a TS. The older animals vibrated for 5 min developed the same TS (mean TS 34 dB) as the young animals when vibrated for 10 min. The vibration-induced TS showed no recovery within 3 days of observation. In the contralateral ear 4 out of 5 animals showed TS > 20 dB. When exposed to sound levels exceeding the vibration-generated sound in the middle ear (119 dB at 250 Hz) only 2 out of II animals (18%) showed TS. The frequency of TS and level of TS were significantly greater in the vibrated animals than in sound-only exposed animals (p < 0.01). The degree of vibration-induced TS in the present animal model could be controlled by vibration intensity and duration. The older animals were more susceptible to vibration-induced inner-ear damage than younger animals. This model will be used in further studies to find methods for prevention and treatment of hearing loss during ear surgery.

To evaluate distant effects of hand-arm vibration we studied Finnish forestry workers using chain saw during the years 1972 through 1990. The hearing was tested annually and individual regression curves for sensorineural hearing loss (SHL) were calculated. Robinson's model was used in prediction of SHL. The heart rate variation (HRV) indexes at rest and during deep breathing test were analyzed to measure autonomic nervous function. In Robinson's model the measured SHL (17.8 dB) respected the predicted SHL (17.2 dB). The subjects with VWF had on average, 10 dB greater hearing loss than those who did not have VWF. The regression model based increase of hearing loss during follow up correlated with ageing, not to VWF. The intercept differed significantly in those with VWF from those without VWF. We found a significant difference between HRV indexes during deep breathing test in those with the shortest and those with the longest vibration exposure. The HRV decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with HRV indexes. Our results suggest that prolonged exposure to vibration caused by chain saw has negative effects an autonomic functions. The aggravated hearing loss in subjects with VWF may be due to vibration induced changes in the autonomic nervous system or internal factors of the blood vessels.

The number of annually compensated occupational diseases due to exposure to hand-arm vibration (HAV) has decreased during the last 15 years. The number of exposed workers has been declining in Finland, especially in forestry work, as harvesters have increasingly replaced manual chain saw operations. During the entire 1970s, forest work caused more cases of vibration-induced occupational diseases than all industrial branches together. The decrease is mainly due to the technical development of chain saws, but also to the effective health care services in Finland. Other factors such as warm transport, warm rest cabins in which to take pauses at work, warm meals, adequate protective clothing, and vocationally adjusted early medical rehabilitation have helped to cut down health hazards, especially in forest work. The number of new cases has been decreasing in Finland not only in forestry but also in other industries. In Finland a considerable amount of research has been conducted to hand-arm vibration, resulting in the increased awareness of the health risks related to certain occupations. This has helped to carry out the Primary Health Care Act (1972) followed by the Occupational Health Care Act (1979) which obligates employers to arrange occupational health care for their employees. We believe that the research activity has contributed significantly to achieving the present health in Finnish work places. The purpose of the present paper is to describe the cases of occupational exposure to HAV, and the effectiveness of different preventive measures in Finland.

The EEG and heart rate reactions to vibration stimulus were studied in 14 patients during moderately deep surgical isoflurane anaesthesia, at a level when EEG showed a burst suppression pattern. Vibration applied to the palm of the hand induced bursts in EEG in 12 patients, usually with a latency of about 0.5 sec from the onset, or from the end of the 3 sec stimulus. Increases in heart rate were seen at bursts related to both vibration onset and offset, as well as at spontaneous bursts. With spontaneous bursts, an initial positive wave was frequently seen. In 6 patients the vibration induced bursts were different in shape from the spontaneous bursts; no initial positive wave was seen before the negative DC shift in Cz-Fz recording. We conclude that EEG bursts can be evoked by a non-noxious stimulus such as vibration in patients during isoflurane anaesthesia.

The effect of a fore-aft oscillating platform on postural stability was studied in nine healthy volunteers. The force platform technique was used with automatic analysis that evaluated the position of the center point of force as a function of time. The duration of stimulation lasted 90 s and the perturbation frequencies ranged from 8 to 24 Hz, and were given at constant rms acceleration of 4 m/s2. When compared with a vibration-free baseline stance, horizontal vibration of the platform caused significantly worse postural stability in all subjects. Test frequencies of 8 and 10 Hz produced greater sway velocities than perturbation at frequencies of 14 and 16 Hz. The results indicate that horizontal perturbation of the support surface leads to postural instability that is frequency-dependent.

A longitudinal study on vibration syndrome among professional forest workers was carried out in Finland from 1972 to 1990. In the course of the follow-up the weighted vibration acceleration of chain saws decreased from about 14 to 2 m/s2. The prevalence of vibration-induced white finger (VWF) decreased gradually from 40% to 5%. Numbness occurred mainly at night, and its prevalence decreased from 78% to 28%. During part of the follow-up period (1975-1990) the complaints of hand muscle weakness decreased from 19% to 9%. Disorders of the musculoskeletal system were considered to cause more disability than VWF. The decreased vibration acceleration and the lighter weight of chain saws were considered the main reasons for the decrease in the prevalence of vibration-induced symptoms.

The importance to postural control of the mechanoreceptors of the soles was investigated in thirteen healthy subjects. Body-sway velocity was evaluated before and after exposing the subject's feet to hypothermia, and when calf muscles were exposed to vibration at frequencies between 20 and 100 Hz. Subjects were tested both with eyes open and closed. Body-sway velocity was found to increase significantly during hypothermia of the feet. The difference in body-sway between hypothermal and normothermal conditions was less prominent when the subject's eyes were open though the difference was significant in both cases. The present results indicate the importance of the mechanoreceptors of the soles to postural control and elucidate their interaction with compensatory visual input in maintaining postural control. These findings also suggest, that factors affecting pressor input should be taken into consideration when assessing patients with complaints of dysequilibrium.

The presence of carpal tunnel syndrome (CTS) in 125 forestry workers with exposure to vibration was examined clinically by electromyography and by determining vibration detection thresholds. Numbness of the hands was present in 43%, history of diminished hand muscle force in 15%, and Raynaud's phenomenon in 27%. The muscle weakness correlated significantly with motor nerve conduction velocity in the median nerve in both hands. In 25 forestry workers CTS was diagnosed. The condition was bilateral in 48%; otherwise it was more common on the right side. Fifteen patients were referred for surgery but because of spontaneous recovery or refusal by the patients only five underwent surgery; of these four improved. The motor conduction velocity of the ulnar nerve was decreased among patients with CTS supporting the idea that entrapment neuropathies in the hands may be due to tissue swelling caused by vibration at work. Total exposure time to vibration correlated with the decrease in motor conduction velocity in the ulnar nerve.

Raynaud's phenomenon has been considered to be due to activation of the central sympathetic vasoconstrictor reflex, and may represent part of a larger dysfunction of higher autonomic centers. Symptoms, such as sweating disturbances, orthostatic hypotension, insomnia and impotence have been reported to be more common among vibration exposed workers. We studied 217 male forest workers and selected samples of this population for electromyographic (N = 80), autonomic nervous system function, controlled breathing, tilting bed and valsalva manoeuvre (N = 88) tests, and a full clinical neurological examination. Mean alcohol consumption was estimated to be 3.0 kg absolute alcohol/year. The total mean vibration exposure time was 14,100 hours. The prevalence of Raynaud's phenomenon was 5%. The variations in heart rate (HRV) at rest and during deep breathing were observed. The traditional indexes of HRV (CV, CVS, MEAN) were computerized and calculated. There was a significant difference (p less than 0.001) between the HRV indexes during the deep breathing test in those with the shortest and the longest exposure to vibration. The values of HRV indexes were age dependent; and in multiple regression analysis, the total exposure time to vibration had an independent negative association to HRV. Also association of sensory neural hearing loss to Raynaud's phenomenon among vibration exposed workers indicates that there is an involvement of the central nervous system in the pathogenesis of vibration syndrome. The question, does vibration cause permanent changes in autonomic centers of the brain or do these centers only mediate vibration stress to end organs, remains unsettled.

A measuring method for the vibration perception threshold (VPT) of fingers has been developed. The VPTs of 118 and 149 professional forest workers were measured during a compulsory annual health examination in 1979 and 1983, respectively. Also the VPTs of eight pedestal grinders, who were suffering vibration-induced white finger (VWF), were measured in 1979 and 1983. The control group consisted of 20 research workers who had no vibration exposure in the past and no symptoms in their hands. The measuring system for VPT gave repeatable results. The frequency of the most sensitive VPT of vibration exposed workers alternated between 63 and 125 Hz instead of 125 Hz of subjects without vibration exposure. The VPT of the pedestal grinders and forest workers with decreased hand grip force and with vibration-induced white finger were significantly higher than those of the controls. The VPTs of the forest workers decreased slightly and that of the grinders increased from 1979 to 1983. In spite of long vibration exposure in the past and continuing lower level vibration exposure, the increased VPT of forest workers does not seem to be permanent.

Vibration detection threshold (VPT) of 149 professional forest workers was measured during a compulsory annual health examination. The authors' earlier developed measuring method for VPT of finger was modified. The blood circulation of the hand was obstructed for 6 min and VPT was measured 4 min after releasing the obstruction. VPTs of all forest workers increased during obstruction. In forest workers suffering from decreased hand grip force (decreased HGF) the increase of VPT differed significantly from forest workers without symptoms, and VPT in the former group still increased after releasing the obstruction. VPT remained also at the raised level after releasing the obstruction with forest workers suffering from vibration-induced white finger (VWF). Nevertheless, on an individual basis even the modified measuring method failed to discriminate subjects without symptoms from those with symptoms of hand-arm vibration syndrome. The raised VPT and sensitivity for obstruction of blood circulation suggest that the reason for decreased HGF in forest workers may be a consequence of an injury in the peripheral nerves.

The neurological findings of 217 forestry workers were evaluated during a compulsory annual health examination. Vibration detection thresholds were determined for the left hand and foot. The handgrip forces were measured for both hands. A reduction in the vibration detection threshold or handgrip force was not associated with clinical neuropathy. Polyneuropathy was found in 4% of the lumberjacks whereas neuropathy restricted to the arms was found in 7.5% of the lumberjacks. The neuropathic findings were not linked with alcohol consumption but were associated with a history of numbness in the hands and diminished muscle force. The findings support the concept that local vibration can cause neuropathy in the arms, but the mechanism of vibration-induced neuropathy still remains uncertain.

Postural control is maintained by sensory feedback from visual, vestibular and somatosensory receptors. Recently several methods for evaluating postural control have been devised, utilizing an imposed perturbation. Most of these methods use stimuli which simultaneously affect more than one of the sensory feedback loops. In the present paper a posturographic technique is presented with specific loading of the proprioceptive system, using a computer controlled vibratory stimulus and computerized analysis of the results.

Peripheral neuropathy represents a well-known complication from long-term exposure to vibration. In the present study an experimental model is presented with the purpose of analyzing the formation of intraneural edema following vibration exposure. Vibration (82 Hz, peak-to-peak amplitude 0.21 mm) was induced in the hind limb of rats by the use of vibrating electric motors during 4 h/d for 5 d. Tracer techniques (with albumin Evans blue and horseradish peroxidase) were used to study the permeability of intraneural microvessels after the vibration exposure on day 5. It was found that the vibration trauma in this model induced epineurial edema in the sciatic nerve. It is hypothesized that the formation of intraneural edema may be an important pathophysiological factor in the occurrence of vibration-induced neuropathy.

A Békésy audiometer was modified for use in analysis of vibrotactile sensibility of the hand at frequencies ranging from 8 to 500 Hz. In control subjects the "digital vibrogram" has a typical shape, which differs characteristically in patients with carpal tunnel syndrome (CTS). Changes in digital vibrogram usually parallel or precede abnormalities in neurophysiologic tests, and appear long before changes in two-point discrimination (2PD). One-hundred-thirty-two hands of 76 patients diagnosed as having CTS were tested with a vibrometer. Of 113 hands with normal 2PD, the digital vibrogram showed abnormal in 86 cases. Of 19 hands with abnormal 2PD, the digital vibrogram showed abnormal in all but three cases. Twenty-six hands with neurophysiologically normal appearance had abnormal digital vibrogram in 14 cases, while 53 hands neurophysiologically classified as CTS showed abnormal digital vibrogram in 44 cases. It is concluded that the digital vibrogram is a useful tool for early diagnosis of CTS.

The variation in heart rate (HRV) at rest and during deep breathing (6 cycles a minute) of 88 professional lumber jacks was studied using a computer technique. The traditional indexes of HRV (CV, CVS, MEAN) were calculated and the spectral components of the HRV were also computed. There was a significant difference (p less than 0.001) between the HRV indexes during the deep breathing test in those with the shortest (CV = 10.1 +/- 1.1) and those with the longest (CV V 6.2 +/- 0.4) exposures to vibration. The values of the HRV indexes decreased with age, but multiple regression analysis showed that the total exposure time to vibration had an independent negative association with the HRV. There were significant differences in all the frequency bands (frequency related power, FRP) of the heart rate between those with the longest and those with the shortest exposures. The HRV during a deep breathing test is associated with the activity of the parasympathetic nervous system and is decreased in autonomic neuropathies. Our results suggest that prolonged exposure to the vibration caused by a chain saw has a negative effect on the parasympathetic activity and thus causes autonomic dysfunction.

A detailed analysis of risk factors for the development of sensory-neural hearing loss (SNHL) was carried out on 122 forest workers. These forest workers were selected from a larger group (n = 217) by restricting the age range to 30-55 years. The hearing threshold of the left ear at 4000 Hz was measured and the effect of age, exposure, systolic and diastolic blood pressure (DBP), presence of vibration-induced white finger (VWF), tobacco smoking and use of earmuffs were evaluated in multiple linear regression analysis. Robinson's nonlinear model was used to evaluate the rate of hearing loss. Aging was the major risk factor and it explained 15.4% of the variance of the SNHL. The presence of VWF was the second most important single risk factor and explained a further 5.2% of the SNHL. Elevation of DBP correlated significantly with SNHL and explained an additional 4.1% of the SNHL. These main factors were able to explain about 26% of the spread of SNHL. Additional factors in the analysis, e.g. smoking, systolic blood pressure, did not significantly contribute to the genesis of SNHL. When Robinson's model was applied to the SNHL data, on a group basis, we did not observe any exaggerated risk of hearing loss due to combination of noise and vibration. In combined exposure subjects with VWF as well as subjects with enhanced DBP will run a higher risk for SNHL.

On the basis of experience accumulated over the past few years, a revision has been made in the currently used Taylor-Pelmear scale for the staging of Raynaud's phenomenon in persons exposed to vibration from hand-held tools, while retaining as much as possible of the well-established advantages of the scale for research and its proved usefulness for clinical and medicolegal purposes. The 0T and 0N stages of symptoms have been omitted, together with the parallel disability scale. A separate staging for neurological disorders connected with the syndrome was proposed and accepted at the workshop "Symptomatology and Diagnostic Methods in the Hand-Arm Vibration Syndrome," held in Stockholm in 1986. The criteria descriptions have been changed so as to minimize their reliance on seasonal factors. The new staging system--a stage 0 and four stages (1-4) with attacks of cold-induced Raynaud's phenomenon--clearly defines the differences in the descriptions of the stage criteria in order to improve their clinical usefulness. A numerical scoring based on the extent and distribution of finger blanching was not, however, introduced, whereas a score based on the number of affected fingers on each hand was proposed, considered, and accepted.

Impulsiveness is defined as the difference between peak and root-mean-square signals. As the difference varies in time, the cumulative distribution function has been used to describe the probability of achieving a certain value of impulsiveness. To make numerical comparison of different vibration signals possible, an impulse index has been selected from the cumulative distribution function. Symptoms of vibration-induced white finger were observed and compared to those expected on the basis of measurements taken according to guidelines of the International Organization for Standardization (ISO). Agreement was found for chain-saw vibration. In the case of pedestal grinding, the ISO draft underestimated the hazardous effects of vibration. Stone workers using pneumatic hammers were exposed to highly impulsive but asymmetrical vibration. The corresponding asymmetry was not, however, observed between the symptoms of the left and right hands, a finding which indicates that coupling between the tool and the hand is important for impulse vibration. The results suggest that the impulse character of vibration increases the risk of vibration-induced pathology. The analysis of high-impulse acceleration peaks obtained by the method presented in this study could provide additional data necessary to improve risk assessment.

A longitudinal study of hearing loss was conducted among a group of lumberjacks in the years 1972 and 1974--8. The number of subjects increased from 72 in 1972 to 203 in 1978. They were classified according to (1) a history of vibration-induced white finger (VWF), (2) age, (3) duration of exposure, an (4) duration of ear muff usage. The hearing level at 4000 Hz was used to indicate the noise-induced permanent threshold shift (NIPTS). The lumberjacks were exposed, at their present pace of work, to noise, Leq values 96-103 dB(A), and to the vibration of a chain saw (linear acceleration 30-70 ms-2). The chain saws of the early 1960s were more hazardous, with the average noise level of 111 dB(A) and a variation acceleration of 60-180 ms-2. When classified on the basis of age, the lumberjacks with VWF had about a 10 dB greater NIPTS than subjects without VWF. NIPTS increased with the duration of exposure to chain saw noise, but with equal noise exposure the NIPTS was about 10 dB greater in lumberjacks with VWF than without VWF. With the same duration of ear protection the lumberjacks with VWF consistently had about a 10 dB greater NIPTS than those without VWF. The differences in NIPTS were statistically significant. The possible reason for more advanced NIPTS in subjects with VWF is that vibration might operate in both of these disorders through a common mechanism--that is, producing a vasoconstriction in both cochlear and digital blood vessels as a result of sympathetic nervous system activity.

Pulse wave changes were examined among 63 professional lumberjacks. The tests were carried out in connection with an annual health examination. A photoelectric plethysmographic method was used to measure pulse wave changes during contralateral muscle work and vibration exposure from a dynamic shaker with a strain-gauge dynamometer. The relative changes in pulse wave amplitude were counted, and the changes were classified as dilatations, constrictions, or constant pulse wave amplitude. Contralateral muscle work caused vasodilatation, but vibration exposure could cause vasoconstrictions in the right hand. Most of the vasospasms were recorded at 60 and 100 Hz. The strongest vasospasms were seen at 200 Hz. The occurrence of vasospasms in the contralateral hand correlated with the severity of white finger symptoms rated according to an index for traumatic vasospastic disease.

A computerized posturography system is composed of a custom made strain gauge force platform and it utilizes commercially available amplifiers. The body sway response signals are digitized for the calculation of the following parameters by a computer: average velocity of body sway, mean value for fore-aft and lateral body sway, and maximal amplitude of body sway. Calf muscles were exposed to vibration to disturb the postural control. The program contains appropriate filters to remove transient and quantification noise.

The hand grip forces at the front and rear handles of a chain saw were measured during work, in 89 professional lumberjacks. The symptoms caused by vibration to the upper limbs were compared with the hand grip force (HGF) during work. To allow better comparison between subjects we used the ratio of hand grip force (HGF) to the maximal voluntary compression force (MVC), HGF/MVC expressed as a percentage. The mean HGF during sawing varied from 5 to 12 N in all subjects. The variation in HGF was greater at the front handle than at the rear handle, during sawing. The lumberjacks who had vibration-induced white fingers (VWF), had a higher HGF/MVC in both hands than the lumberjacks without VWF. Those lumberjacks affected by VWF used over 12% of their MVC at work. Subjects without HGF/MVC ratio. The lumberjacks with and without numbness in their hands had equal HGF/MVC ratios.

Eye movements and the electroencephalogram (EEG) were recorded in intact rabbits during an optokinetic test when the animals were exposed to pure-tone sound (85 dB at 4,000 Hz), impulse noise (159 dB), and vibration directed to the abdomen (at an amplitude of 0.9 mm at frequencies of 40 to 140 Hz). The frequency and velocity of optokinetic nystagmus significantly increased in response to these stimuli. The increase seen with vibration was greater than that resulting from sound, and the response was strongest when sound and vibration were combined. The increase of optokinetic nystagmus seen with induced vibration was progressive and dependent on the frequency. The increase was weakest during vibration at 40 Hz and strongest during vibration at 140 Hz. Electroencephalograms (EEGs) of the amygdaloid complex, dorsal hippocampus, midbrain reticular formation, and frontal motor cortex all were activated during exposure to sound and vibration, but activation of the hippocampal EEG was most closely related to the increase of optokinetic nystagmus. During optokinetic tests, impulse noise regularly triggered nystagmic beats. When the rabbits were not in the test apparatus, nystagmus was produced in response to about 18 per cent of the presentations of impulse noise, while activation of the EEG was constant. Thus, vibration and noise, when excessive, may interfere with visual orientation and hence disturb equilibrium. These findings can be related to the nonspecific dizziness that occurs in aerospace or industrial workers exposed to excessive noise and vibration.

Finger systolic blood pressure (FSBP), finger arterial inflow (FAI), finger venous opening pressure (FVOP), and finger peripheral resistance (FPR) were evaluated in 56 workers exposed to chain-saw vibration. Twenty-one of the workers were free from vibration-induced white finger (VWF). In 17 subjects VWF had ceased; 12 of the subjects had active VWF; 6 subjects had Raynaud's disease. The subjects were examined in a supine position under thermoneutral conditions with strain-gauge plethysmography. Cold provocation of the finger caused a significant reduction in FSBP in the groups with Raynaud's disease and active VWF. The finger circulation of the subjects with active VWF and that of those with Raynaud's disease showed a significantly reduced FAI when compared with that of the symptom-free referents. Finger cooling produced a gradual reduction in the FVOP and a significantly increased FPR of the subjects with active VWF and in those with Raynaud's disease. FPR was already increased in the Raynaud's disease group at the beginning of the test, whereas it increased in the VWF group as the temperature fell. The results suggest that in Raynaud's disease the fault is in the level of activity of the sympathetic outflow and in VWF it is peripheral mechanisms controlling the vessel tone.

The relation between noise-induced permanent threshold shift (NIPTS) and vibration-induced dysfunction in the digital circulation was examined in a longitudinal survey among forest workers. The survey was based on annual examinations done between 1972 and 1983. Thirty-two forest workers with digital vasospasms were compared with referents matched for age, exposure, and use of ear protectors. No significant differences between the groups were observed at 1,000 or 2,000 Hz. The forest workers with digital vasospasms had significantly greater NIPTS at 4,000 and 8,000 Hz than the symptom-free referents. During the follow-up period, the gap in NIPTS between the two groups did not increase. Vibration measurements from chain saws manufactured in different years indicated that chain saws manufactured after 1970 had a tenfold reduction in vibration, whereas the reduction in noise levels was only slight. The results suggest that vibration-induced activation of the autonomic nervous system, which is thought to elicit digital vasospasms, may also contribute to the development of NIPTS.

Neurological findings were examined in 186 forestry workers with a mean exposure to chain saw vibration of 16.6 hours. The prevalence of active vibration induced white fingers was 5%, parethaesias of the hands 53%, and muscle weakness 13%. Clinical polyneuropathy was observed in 16 forestry workers in the hands (7.5%) which did not correlate with alcohol consumption. Seventy nine forestry workers of the total population were selected for electromyographic examination. Generalised EMG based polyneuropathy in the hands was observed in only two of the 79 forestry workers (2.5%). The carpal tunnel syndrome was found in 20 of the 79 forestry workers (26%). Headache and vertigo were not linked with exposure to vibration in forestry and a significant part of the numbness reported may be due to the carpal tunnel syndrome. Sensorimotor polyneuropathy is rare among forestry workers. The rise in the vibration detection thresholds was linked to the carpal tunnel syndrome.

At present it seems likely that the different components of the hand-arm vibration syndrome, eg, vibration-induced white finger (VWF), numbing of the hands and arms, muscular fatigue, and occasionally prevalent bone degeneration, may arise independently, and therefore they should be evaluated separately. Evidence of changes caused in the autonomic nervous functions of the body by local vibration is not conclusive. The vascular history should be confirmed objectively with a cold provocation test under laboratory conditions. In individual diagnostics it is useful to record (with modern plethysmographic techniques) the recovery of digital temperature, digital blood pressure, and flow after local cooling. Vibrotactile perception measurement seems to be suitable for group diagnosis. Much of the diagnostic weight for VWF can be obtained from accurate case histories, although, for early changes, the history may be atypical. The lack of simple objective tests for evaluating the hand-arm vibration syndrome makes it difficult to, eg, confirm the history of its different components objectively and estimate the extent of the disability it causes.

The relationship between electroencephalogram (EEG) and eye movements was studied in rabbits during optokinetic, vestibular, and optovestibular tests. EEG was recorded through permanently implanted electrodes. Exposure to noise and vibration increased the frequency and the velocity of optokinetic nystagmus (OKN). The increase was greater during vibration but greatest during combined noise and vibration. EEG activity was closely linked to changes in OKN and was particularly evident with the appearance of theta waves in the dorsal hippocampus. Also, rotation of the rabbit produced considerable activation in the EEG.

Isometric maximal hand grip force was measured with a strain gauge dynamometer in 91 lumberjacks and 31 controls during a 2-min compression-relaxation task. Measurements were carried out on both hands with and without simultaneous vibration exposure. The muscle forces of older subjects were smaller than those of younger men, independent of occupational vibration exposure. The fatigue curves of lumberjacks and control subjects had the same shape. During vibration exposure in the test, the forces diminished in the left hand significantly in the lumberjacks but not in the control subjects. The force level of fatigue curves of the lumberjacks with a history of diminished grip force was lower and decreased more during vibration exposure than in the lumberjacks with a history of normal grip force. The reduction in the hand grip force during vibration exposure in the lumberjacks seemed to be linked to lesions in the peripheral nerves and to activation of a tonic vibration reflex, but probably not to circulation disturbances. The fatigue mechanism seemed to be the same in lumberjacks and control subjects.

Two types of cold provocation tests, a classical test with immersion of the hand in cold water and the evaluation of finger systolic blood pressure (FSBP) during local cooling, were administered to forest workers. Raynaud's phenomenon in the classical test correlated positively with the number of disabled phalanges, recovery time, and frequency of attacks. It did not correlate with the severity of paresthesia of the hands and arms. Repetition of the test enhanced the number of positive results. A significant reduction in the FSBP was observed in 22 and 25% of the subjects with inactive and active forms of vibration-induced white finger (VWF), respectively. In the same groups of subjects the classical cold provocation test yielded positive results in 7 and 25% of the subjects, respectively. A cold provocation test was found to produce a positive result even some years after the cessation of VWF attacks. The rather low severity of VWF among the examined subjects may explain the lack of positive test results. FSBP measurement was not superior to cold provocation by water immersion, but it is recommended because it is easier to standardize and more convenient for the test subject.

A review of current knowledge on the pathophysiological and hygienic aspects of the hand-arm vibration syndrome is given. Hemodynamic measurements indicate that the primary factor in vibration-induced white finger is an increase in the peripheral resistance of finger circulation that is present after local and general cooling. The reason for this increase is not known, but it is postulated that an excessive affinity of vasoactive substances for the efferent receptors exists, this affinity being potentiated during local cooling of the digits. So far, the hygienic rating of hazardous vibration in individual work phases is of limited value in diagnosing possible cases, but this rating does provide guidelines for general risk assessment. A consideration of several factors, eg, intermittency of the work, duration of daily exposure, impact of vibration, individual physiological responses, climate, etc, might improve the accuracy of the rating, but the influence of these factors on the development of the vibration syndrome is still poorly understood. Of various preventive measures, only those that significantly reduce vibration will be beneficial in the long run.

Vasomotor oscillation at different ambient temperatures, with and without anesthesia of the finger nerves, was studied in six persons with vibration-induced white finger (VWF) and in 10 referents. The power spectral density (PSD) of the Fourier transform of the laser-Doppler flowmeter signal from the finger pad vessels was analyzed. In both groups, the PSD of the vasomotor oscillation in the frequency range of 0.05-0.25 Hz was more pronounced in a cold than in a hot environment. Without finger nerve anesthesia, the oscillations of the referents were significantly greater (p less than 0.01) than those of the VWF subjects (PSD -34.4 dB and -41.6 dB, respectively). With anesthesia of the finger vasomotor nerves, the PSD was reduced in both groups. In the anesthetized finger there was no statistically significant group difference. Thus the myogenic component of the vasomotor activity was the same in the referents as in the VWF subjects. The results show that the autonomic neural influence on vasomotor oscillation in skin of the finger pad is weaker in persons with VWF. This weakness may be a sign of peripheral neuropathy, which may lead to a denervation syndrome causing hypersensitivity of the adrenoceptors to cold.

Central nervous, sympathetic mechanisms and local factors influencing the vascular response to cold in the finger skin were studied with plethysmographic and laser-Doppler methods in a chamber with controlled temperatures from 45 to about 5 degrees C, with and without sympathetic finger blockade. Blood flow and pressure were assessed after finger occlusion, together with finger heating and cooling, in workers with vibration-induced white finger (VWF) and in healthy persons not exposed to cold or vibration. Finger blood flow at vasodilatation, as measured by finger arterial inflow (FAI) after occlusion was smaller in the VWF group than in the reference subjects both with and without anesthesia, and capillary flux in the anesthetized finger tended to be smaller. At vasoconstriction, with or without anesthesia, the VWF subjects had lower FAI values than the referents. The studied flow and pressure variables differed considerably between the groups. The peripheral resistance of the VWF subjects was higher than that of the referents. This difference was the most pronounced after finger anesthesia. A possible pathogenetic mechanism in VWF is an increase in peripheral resistance due to a local defect in the vessels, with subsequent reduction in flow and intramural pressure.

The peripheral circulation was studied in 19 lumberjacks and in 12 control subjects. Twelve of the lumberjacks were free from vascular symptoms and seven had vibration induced white finger (VWF). Using the strain-gauge plethysmographic technique, the digital circulation was examined at rest, during cooling of the upper body, and during heating of the upper body. At rest and during vasodilatation no significant differences were found between the lumberjacks and the controls. During reflexive vasoconstriction, digital blood flow in the upper body was more reduced in lumberjacks with VWF than in control subjects. Furthermore, digital blood pressure of the lumberjacks with VWF fell more than in the control group. The peripheral resistance also increased more, but this difference was not statistically significant. There was no evidence that the exaggerated vasoconstriction of VWF resulted from a narrowing of the lumen of arterioles due to hypertrophy of the vessel wall. The present findings suggest that VWF is produced by the highly sensitive responsiveness of the affected vessel to normal vasoconstrictor stimuli.

Eye movements and electroencephalographs (EEG) were recorded in intact rabbits during an optokinetic test. The animals were exposed to pure tone noise (85 dB at 4000 Hz), impulse noise (159 dB), and vibration directed at the abdomen (amplitude 0.9 mm at frequencies of 40, 80, and 120 Hz). The velocity of optokinetic nystagmus (OKN) significantly increased with these stimuli. The increase seen with vibration was greater than the noise-induced increase. The response was strongest when noise and vibration were combined. The increase in OKN induced by vibration was successive and dependent on frequency. The increase was weakest during exposure to vibration at 40 Hz and strongest at 120 Hz. EEGs of the dorsal hippocampus, amygdaloid complex, midbrain reticular formation, and frontal motor cortex were all activated during noise and vibration exposure, but activation of the hippocampal EEG was the most closely related to the increase in OKN. Combination of the different stimuli indicated that their interaction could not be predicted on the basis of responses to single stimuli, and, in most cases, the result was indifference due to the high alerting effect of vibration alone. The findings can be related to the non-specific dizziness found in aerospace workers exposed to excessive noise and vibration.

An analysis of electroneurographic studies of workers who operate hand-held vibrating power tools reveals that, when controlled for polyneuropathy and the effects of heavy manual work, significantly reduced sensory nerve conduction velocities occur within the hands. This finding is compatible with the available pathophysiological evidence. The detection of this presumed vibration-induced neuropathy and its distinction from compression neuropathies involving a localized primary lesion, such as carpal tunnel syndrome, thus requires a detailed investigation of nerve conduction within the hands. A technique well adapted to the detection of abnormalities in the most peripheral sensory nerve fibers and mechanoreceptors has been developed based on vibrotactile stimulation of a fingertip. The compound action potentials recorded noninvasively at the base of the finger and wrist from healthy male subjects possess peak-to-peak amplitudes of no more than 0.5 and 0.25 microV, respectively.

The vibrotactile perception threshold has been evaluated in 20 manual workers not exposed to occupational vibration and in 27 workers using hand-held vibrating tools. Threshold values were evaluated with a Békesy type of vibrometer at frequencies ranging from 8 to 500 Hz. The earliest sign of vibration lesion was a reduction of sensation at frequencies of 125 to 250 Hz, indicating dysfunction in receptors of the fast adapting type II (stage 1 curve), followed in more severe cases by a prominent loss of sensation at all frequencies higher than 65 Hz (stage 2 curve). The stage 3 curve indicated the most severe loss of sensation in which the function of slowly adapting type I receptors, as well as fast adapting type I receptors, was deteriorated; consequently the vibrotactile thresholds at low-, median-, and high-frequency ranges were impaired. The vibrotactile changes corresponded well to numbness and the presence of vibration-induced white finger.

A longitudinal survey on the prevalence of vibration syndrome among professional forest workers was conducted from 1972 (118 workers) to 1983 (206 workers). The prevalence of vibration-induced white finger (VWF) was 40% among the workers in 1972; it gradually declined to 5% in 1983. Three new workers developed VWF symptoms during the follow-up period. They had only used saws equipped with antivibration handles. The prevalence of VWF has decreased mainly due to the reduction of chain-saw vibration. The prevalence of paresthesias of the hands and arms declined from 78% in 1972 to 37% in 1976, and then increased to 51% in 1983. The recent increase was thought to be due to static muscle load and the ageing of the workers. No correlation was found between the severity of VWF and peripheral nerve symptoms. No significant changes in muscle fatigue occurred during the follow-up period; it was present in about 10-15% of the workers. The forest workers subjectively assessed musculoskeletal load and strain as being more harmful than the symptoms of vibration syndrome. The preventive measures aimed at reducing chain-saw vibration, implemented since 1970, have been beneficial and explain the decreased prevalence of VWF.

At one Finnish foundry all the workers had typical symptoms of vibration induced white finger (VWF) after they began using a new type of pedestal grinding machine. The objectives of this study were to establish the severity of the symptoms and the difference in vibration exposure between the new and the old machines. Vibration detection thresholds and grip forces were measured, as well as the vibration in the casting and in the wrist simultaneously. The mean latency for VWF among the grinders was 10.3 months after the change of pedestal grinding machines. All the grinders had numbness in their hands. The vibration detection threshold was significantly higher for the grinders than for their referents. At the same circle speed, the new wheels caused vibration levels up to 12 dB more than the old wheels. The circle speed had a slight influence on the vibration. The vibration levels of light (0.5 kg) casting were up to 25 dB higher than the heavy (5 kg) casting. The use of a pneumatic pressing device decreased the vibration levels in the wrist by 5-10 dB. The increase in vibration, which occurred when the new wheels were taken into use, was too small to explain such a dramatic outbreak of VWF. This led to the conclusion that some other feature such as the impulse character of the vibration also contributed to the effects of vibration.

A review of current knowledge on the pathophysiological aspects of peripheral circulatory derangements in the hand-arm vibration syndrome is presented. Hemodynamic measurements indicate that the primary factor in vibration-induced white finger is an increase in peripheral resistance of finger circulation, present after local and general cooling. The reason for this increase is not known, but it is postulated that there is an excess affinity for the efferent receptors of vasoactive substances and that this affinity is potentiated during local cooling of the digits.