Vibrotactile Perception Thresholds Research Articles

Vascular and nerve damage in workers exposed to vibrating tools. The importance of objective measurements of exposure time

The aim of the present study was to compare the development of vibration white fingers (VWF) in workers in relation to different ways of exposure estimation, and their relationship to the standard ISO 5349, annex A. Nineteen vibration exposed (grinding machines) male workers completed a questionnaire followed by a structured interview including questions regarding their estimated hand-held vibration exposure. Neurophysiological tests such as fractionated nerve conduction velocity in hands and arms, vibrotactile perception thresholds and temperature thresholds were determined. The subjective estimation of the mean daily exposure-time to vibrating tools was 192 min (range 18–480 min) among the workers. The estimated mean exposure time calculated from the consumption of grinding wheels was 42 min (range 18–60 min), approximately a four-fold overestimation (Wilcoxon's signed ranks test, p<0.001). Thus, objective measurements of the exposure time, related to the standard ISO 5349, which in this case were based on the consumption of grinding wheels, will in most cases give a better basis for adequate risk assessment than self-exposure assessment.

Vibration perception thresholds of human maxillary and mandibular central incisors

Tactile information from dental mechanoreceptors contributes to the perception of food bolus textures and the control of mastication. While numerous studies have measured the light-touch sensory thresholds of teeth, little information is available about the vibrotactile perception thresholds of teeth. This study uses an adaptive psychophysical procedure to determine thresholds of vibratory stimulation of maxillary and mandibular central incisors in 16 healthy human subjects. An electromechanical vibrator delivered labiolingual forces perpendicular to the long axis of the maxillary and mandibular incisors at 10 stimulation frequencies between 40 and 315 Hz. The median thresholds ranged between 44 and 104 mN. A linear regression analysis revealed a significant increase in the vibrotactile thresholds with increasing frequencies for stimulation of the maxillary and mandibular incisors. No significant differences were found between regression slopes of the thresholds of the maxillary and mandibular incisors. These results indicated that maxillary and mandibular incisors should be able to discriminate effectively among a variety of textures based on their ability to encode a wide range of vibration frequencies.

Effects of Static Compression on the Vibration Modes of a Fingertip

The vibrotactile perception threshold measurement technique is used to diagnose sensory neuropathy of the hand. The vibration perception threshold of a human finger could be most sensitive in the vicinity of one or more of its resonant frequency. The purpose of the present study is to investigate, theoretically, the effects of deformation (compression) on the free vibration behaviour of fingertips. An in-plane finite element model of the fingertip tissue has been formulated on the basis of the anatomical structure and the nonlinear elastic material properties of the soft tissue. The vibration modes of a fingertip model have been analyzed under different deformation states. Our results show that the modal vibration characteristics of the fingertip are deformation-dependent; the eigenfrequencies of the fingertip increase with the increasing preload. The present study suggests, from a theoretical point of view, that the static deformation state will influence the vibration modes and thus the perception threshold of fingertips.

Vibrotactile perception thresholds in four non-exposed populations of working age

The purpose of this study was to establish a basis for the use of a device for measuring vibrotactile perception thresholds for epidemiological purposes on a series of non-exposed populations. Vibrotactile perception thresholds (VPTs) were measured with a vibrometer in 218 men and 160 women belonging to two non-exposed male blue collar populations, one white-collar population and one age and gender stratified sample of the general population. VPTs were measured on the middle and the little finger of the dominant hand at 31.5 and 125 Hz. The VPTs were expressed in dB and the effect of a series of factors including the population, age, gender and digital temperature was assessed in a regression analysis weighted by the inverse variance of the measurements. Adjusted for age, no significant difference between the VPTs in the four male populations was observed. At frequency 125 Hz, the effect of age (0.3 dB per year) was more important than at frequency 31.5 Hz (0.2 dB per year). In the two female populations, the results were less stable than among males and the VPTs were higher than among males. However, the age-dependence was similar among males and females. The within-test variance is a valuable indicator of the quality of the VPT measurements. Weighting by its inverse improved the fit of the regression models. Normal values for VPTs in non-exposed populations were obtained, which were reproducible in four separate populations.

Vibrotactile perception thresholds in four non-exposed populations of working age

The purpose of this study was to establish a basis for the use of a device for measuring vibrotactile perception thresholds for epidemiological purposes on a series of non-exposed populations. Vibrotactile perception thresholds (VPTs) were measured with a vibrometer in 218 men and 160 women belonging to two non-exposed male blue collar populations, one white-collar population and one age and gender stratified sample of the general population. VPTs were measured on the middle and the little finger of the dominant hand at 31.5 and 125 Hz. The VPTs were expressed in dB and the effect of a series of factors including the population, age, gender and digital temperature was assessed in a regression analysis weighted by the inverse variance of the measurements. Adjusted for age, no significant difference between the VPTs in the four male populations was observed. At frequency 125 Hz, the effect of age (0.3 dB per year) was more important than at frequency 31.5 Hz (0.2 dB per year). In the two female populations, the results were less stable than among males and the VPTs were higher than among males. However, the age-dependence was similar among males and females. The within-test variance is a valuable indicator of the quality of the VPT measurements. Weighting by its inverse improved the fit of the regression models. Normal values for VPTs in non-exposed populations were obtained, which were reproducible in four separate populations.

Changes over a workshift in aesthesiometric and vibrotactile perception thresholds of workers exposed to intermittent hand transmitted vibration from impact wrenches.

OBJECTIVES: To investigate the changes over a workshift in fingertip tactile perception thresholds in users of impact wrenches exposed to intermittent hand transmitted vibration. A further aim was to assess...

Health effects in the upper extremeties of persons operating low-vibration power tools

A group of manual workers (N=18) who operate low-vibration power tools (|ahw|max&amp;lt;2 m s−2) has been examined for objective evidence of work-related changes in hand and arm function. The subjects were drawn from and selected to be representative of a cohort of chain saw operators (N=124) whose health has been followed prospectively, 30% of whom reported experiencing numbness in the upper extremities. A method for detecting a statistically sufficient change in tactile acuity from measurements of mechanoreceptor-specific vibrotactile perception thresholds conducted over a 5-yr interval has been developed, together with any shift in acuity from the value occurring in healthy persons. A progressive deterioration in acuity was found in 12/36 hands, which is predicted to result in abnormal acuity in 39% of the group after a further 5 yr of work. The subjects predicted to be most severely affected currently exhibit reduced hand grip, and reduced hand and arm strength.

Method and system for identifying vibrotactile perception thresholds of nerve endings with inconsistent subject response rejection

ABSTRACT A method of identifying vibrotactile perception thresholds of nerve endings at a skin site of a subject to assess sensory change in tactile sensory nerve function is disclosed. The method comprises applying two known frequencies in the frequency ranges mediated by three types of nerve ending groups to obtain a sensory response from a subject as the amplitude of these frequencies is increased and decreased. These responses are converted into threshold signals of which threshold shift values are established, the deviation of which is then compared with a stored reference inconsistency limit value which was derived from healthy intra-subject variability, in order to determine the acceptanc or rejection of the threshold signal values derived from the subject. If the threshold signal valu? are rejected, the test is repeated several times until acceptable threshold signal values are obtained thereby providing a true tactogram response of the subject.

Changes in mechanoreceptor‐specific vibrotactile thresholds with ongoing occupational exposure to hand‐transmitted vibration

The purpose of this paper is to explore the influence of occupational exposure to hand‐transmitted vibration on mechanoreceptor acuity, for possible future use as a screening test for early symptoms of the hand–arm vibration syndrome (HAVS). Mechanoreceptor‐specific vibrotactile thresholds were determined using the tactometer at frequencies mediated by the SAI receptors (4 Hz), FAI receptors (32 Hz), and FAII receptors (100 Hz) [A. J. Brammer and J. E. Piercy, ‘‘Measuring vibrotactile perception thresholds at the fingertips of power‐tool operators,’’ Proc. U.K. Informal Group Meeting on Human Response to Vibration, Buxton (1991)]. Thresholds were obtained from 33 seasonal operators of chain saws and brush cutters, who had so worked for up to 39 years. Twenty‐three of the workers were judged clinically to suffer from mild to moderate symptoms of HAVS. A progressive reduction in acuity with increasing years of exposure was observed, on average, in this group, for each mechanoreceptor population. A reduction in acuity remained even after correcting for changes in threshold with age.

Age-related changes in mechanoreceptor-specific vibrotactile thresholds for normal hands

Mechanoreceptor-specific vibrotactile perception thresholds have been measured at the fingertips using the tactometer [A. J. Brammer and J. E. Piercy, in Proc. UK Informal Group Meeting on Human Response to Vibration, Buxton (September 1991)]. Thresholds were obtained from the left and right hands of healthy male white-collar workers, aged from 25 to 73 years, without signs, symptoms, or history of neurological disease, or of exposure to vibration. Groups were formed from: (1) oriental professionals (mean age 34±5.9 years, N=24); (2) occidental professionals (mean age 40±5.0 years, N=18); and (3) oriental workers (mean age 62±5.6 years, N=24). A preliminary analysis of the data suggests that there is little effect of age on thresholds mediated by the SAI and FAI receptors. Thresholds mediated by the FAII receptors decreased in sensitivity at a average rate of 2.6 dB per decade increase in age. There are also a tendency for the SAI and FAI receptor thresholds in groups 1 and 3 to be more sensitive than those in group 2.

Vibrotactile perception threshold measurements for diagnosis of sensory neuropathy. Description of a reference population.

Recognition of the fact that impairment of the tactile sense may occur independently of other disturbances in the vibration syndrome has rekindled an interest in developing a diagnostic method for early detection of vibration-induced neuropathy. There is also evidence suggesting that vibrotactile measurements represent a valuable diagnostic tool in compressive neuropathies, such as the carpal tunnel syndrome. The method may also become useful for diagnosing sensory neuropathies caused by other factors, such as solvents, pesticides, heavy metals, alcoholism, and diabetes. However, before vibrotactile measurement can be accepted and established as a tool for clinical diagnostic purposes, for screening, and in research, the level and the shape of the normal threshold curve have to be specified. With the purpose of assembling normative data, the vibrotactile perception thresholds (8-500 Hz) of the right index fingertip were measured in 171 healthy males (19-75 years) not exposed to vibration. A Békésy audiometer was modified to operate in combination with a vibration exciter, instead of headphones, at frequencies lower than usual (8-500 Hz). The results showed that the perception thresholds increased from about 100 dB to about 140 dB (rel. 10(-6) m/s2rms) as a function of frequency and age. The frequency-dependent changes were not linear, however, but displayed a peak in sensitivity at 125 Hz. Threshold changes due to aging were most pronounced at the highest frequencies. It is of the utmost importance that these natural changes are taken into account when making comparisons between groups or individuals.

Measurement precision of a portable instrument to assess vibrotactile perception threshold

The objective of the present study was to evaluate the reliability of a modified version of the commercially available Biothesiometer, and to examine vibrotactile perception thresholds with respect to age and gender. A standardized protocol for measuring vibrotactile perception threshold was administered to 80 subjects, once a week over 4 weeks. Inter-session variability was stable (analysis of variance for repeated measures; P greater than 0.05) and correlations were high (Pearson's: 0.87 less than or equal to r less than or equal to 0.90; P less than or equal to 0.001). For sites on both hands and feet, there was a significant increase with age (0.19 less than or equal to r2 less than or equal to 0.52; P less than or equal to 0.001). Five factor analysis of variance model showed that vibrotactile perception threshold was significantly different with stimulus site, age category and gender; no differences were observed with alcohol consumption or smoking status. The findings indicate that the measurements from this device are highly reproducible and sensitive to expected threshold differences with age and gender. The authors attribute this to technical improvements of the original apparatus, rigid adherence to test protocol and maintenance of standard conditions. This type of instrument would be useful in assessing vibrotactile perception loss in occupational health studies.

Detection of peripheral sensory nerve dysfunction: A preliminary comparison of nerve conduction and mechanoreceptor-specific vibrotactile thresholds

Using the method described previously, mechanoreceptor-specific vibrotactile perception thresholds have been determined at the fingertips (digits 3 and 5) of a series of 24 chain saw operators, 83% of whom reported symptoms of intermittent or persistent numbness, and/or episodic white fingers. Motor and sensory nerve conduction velocities were then recorded from the median and ulnar nerves in each hand and arm, as well as motor distal latencies, following conventional procedures. If the results are compared with normative values from nonvibration exposed, symptom-free, manual workers (and the limit of normality is taken to be two standard deviations from the mean value), 71% and 29% of sawyers reported symptoms are found to possess abnormal vibrotactile thresholds and sensory nerve conduction velocities, respectively. Of the workers at present not reporting symptoms, 50% and 89% are found to possess normal vibrotactile thresholds and sensory velocities, respectively. Performance measures of the two objective tests will be discussed that attempt to account for the subjective nature of symptom reporting.

Assessment of peripheral neuropathies by mechanoreceptor-specific vibrotactile thresholds

Mechanoreceptor-specific vibrotactile perception thresholds have been determined at the fingertips of 79 workers who regularly operate pulpwood chain saws (in Ontario), large-timber chain saws (in coastal British Columbia), or rock drills. The measurement procedure, which involves establishing the sensitivity of three receptor populations (types SAI, FAI, and FAII) from thresholds determined at up to six frequencies from 4 to 200 Hz, has been described elsewhere (A. J. Brammer and J. E. Piercy, Proceedings of the 5th International Conference on Hand-Arm Vibration, Kanazawa, 1989). Even after repeated screening to exclude peripheral neuropathies unrelated to work, and neuropathies confined to either the median or ulnar nerve, the results continue to reveal two patterns of abnormality. Within the group, 21% of hands exhibit similarly elevated thresholds at all frequencies, which is consistent with peripheral nerve degeneration. Thirty-seven hands (26%) exhibit elevated thresholds at frequencies mediated by only one or two receptor populations (almost always SAI and/or FAII types), which is suggestive of receptor-specific degeneration at or near the nerve endings. Seventy-one hands (50%) possess thresholds within the limits of normality.

Vibrotactile perception thresholds in hands occupationally exposed to vibration: Interpretation of sensorineural loss

The tactile performance of the hand is now known to be critically dependent on neural activity in one population of slow‐adapting (SAI) and two populations of fast‐adapting (FAI, FAII) mechanoreceptors. A technique has recently been developed to establish the sensitivity of these receptor populations at the fingertip from vibrational perception thresholds determined psychophysically with sinusoidal stimulation [A. J. Brammer et al., J. Hand Surg. 12A, 870–875 (1987)]. A comparison of data from 98 vibration‐exposed and 34 normal hands, all screened to exclude confounding factors, has revealed two patterns of abnormal threshold elevation. The first, involving similarly elevated thresholds at all frequencies (2–200 Hz), is indicative of sensorineural losses of similar magnitude in each type of receptor‐nerve system, and so is suggestive of peripheral nerve degeneration. The second pattern involves elevated thresholds at frequencies mediated only by one or sometimes two receptor types (commonly SAI and/or FAII). A mechanoreceptor‐specific mechanism is unlikely to occur within a nerve trunk, and so this frequency‐dependent pattern is suggestive of selective damage to the nerve endings.

Tactile perception in hands occupationally exposed to vibration

The sensory changes that occur in hands occupationally exposed to vibration have been assessed clinically by conventional neurologic tests and, independently, by improved techniques for the determination of tactile spatial resolution (gap detection) and vibrotactile perception thresholds at frequencies from 2 to 400 Hz. Data from 10 forest workers who were exposed to chain saw vibration and seven laboratory workers of similar age, all of whom were screened to exclude confounding factors, revealed, for the first time, three patterns of response, two of which are associated with a vibration-induced neuropathy. The first appears to be characterized by normal or better than normal thresholds in SAI, FAI, and FAII mechanoreceptor types, while a second, extreme response involves elevated thresholds in all three receptor systems (and abnormal two-point discrimination). The third pattern appears to be characterized by elevated thresholds in SAI and/or FAII receptor types.

Sensorineural stages of the hand-arm vibration syndrome.

Recent work has shown that the vascular signs and neurological symptoms commonly associated with exposure of the hand to vibration may develop independently. A classification for the neurological component of the hand-arm vibration syndrome has been developed for those symptoms dominated by sensory afferent involvement, based on the results of objective tests on 634 hands. The first symptomatic stage (1SN) consists essentially of episodic finger numbness with or without tingling, the second involves, in addition, reduced sensory perception (2SN), while the most severe stage (3SN) focuses on reduced tactile discrimination and/or manipulative dexterity. Consistent implementation of this classification by means of objective tests requires one, or more, precise, quantitative measure of peripheral somatosensory dysfunction, in addition to the traditional neurological tests (fine touch, pain, and temperature). Measurements of tactile function by means of esthesiometry or vibrotactile perception appear suited to this purpose. A procedure for staging individual hands may then be based on combining numerical scores assigned to the results of the traditional neurological tests and, additionally, esthesiometer and/or vibrotactile perception thresholds.

A new principle for assessing vibrotactile sense in vibration-induced neuropathy.

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.

Assessment of impaired tactile sensation. A pilot study.

Three methods are compared for assessing impaired tactile sensation in vibration-exposed workers: a medical examination including traditional neurological tests and refined measures of vibrotactile perception and gap detection. Of 18 subjects only 12 were judged free of confounding factors--five forestry workers exposed to chain-saw vibration, aged 28 (SD 5) years, and seven laboratory workers not exposed to vibration, aged 36 (SD 7) years. Each method identified the same subject as suffering the most from tactile impairment, but they differed in their ranking of the severity of sensory changes. The ranking by gap detection and vibrotactile perception at low frequencies was the most consistent [Spearman rank correlation coefficient (r) = 0.90]. The clinical results, when staged according to the neurological component of vibration-induced white finger, ranked the thresholds for gap detection and low-frequency vibrotactile perception equally well (r = 0.70). In contrast, the Taylor-Pelmear staging of the clinical results poorly represented the ranking of tactile thresholds recorded for these workers (r = 0.00 and -0.20, respectively). It also appeared that improved techniques for measuring vibrotactile and gap perception thresholds can detect sensory changes in the fingers not consistently found by conventional clinical tests.

Physiological noise and its influence on vibrotactile perception thresholds.

Vibration of physiological origin (physiological noise) was studied when a small diameter probe, attached to a vibrator and accelerometer for the determination of vibrotactile perception thresholds, was held in contact with a fingertip. The acceleration spectrum consisted of a broad plateau between 0.1 and 10 Hz, where the power spectral density was about -20 dB re 1 (m/s2)2/Hz, and it fell rapidly with increasing frequency above 10 Hz. Substantial contributions from respiration (0.2-1 Hz), blood circulation (1-5 Hz), and hand tremor (6-8 Hz) could be identified. The physiological noise was largely independent of subject, contact force, and probe diameter, and it was approximately equal in amplitude to the threshold of the vibrotactile perception. Current knowledge of the masking and adaptation of vibrotactile signals indicates that vibrotactile thresholds in the frequency range 2-250 Hz may be influenced by the magnitude of this physiological noise under some conditions of flesh stimulation.