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

Near-wall hemodynamic parameters of finger arteries altered by hand-transmitted vibration

BACKGROUND

Sustained exposure to high-level hand-transmitted vibrations may result in angioneurotic disorders, which partly originate from vibration-altered hemodynamics in the finger arteries when repeating these disturbances throughout working life. Hence, the aim of this study is to assess the most relevant hemodynamic descriptors in the digital arteries, determine the relationship between the latter and vibration features, and gain better understanding of the physiological mechanisms involved.

METHODS

An experimental setup, mainly comprised of an ultra-high frequency ultrasound scanner and a vibration shaker, was used to image the digital proper volar arteries of the forefinger. Raw ultrasound data were post-processed by custom-made numerical routines to supply a pulsatile fluid mechanics model for computing the hemodynamic descriptors. Twenty-four healthy volunteers participated in the measurement campaign. Classical statistical methods were then applied to the dataset and also the wavelet transform for calculating the signal power in the frequency bands matching cardiac, respiratory, myogenic and neurogenic activities.

RESULTS

The artery diameter, the wall shear stress - WSS - and the WSS temporal gradient - WSSTG - were found to be the most relevant descriptors. Vibration-induced WSS was divided by three compared to its basal value whatever the vibration frequency and it was proportional to log2 of the acceleration level. Marked increases in WSSTG when stopping vibration might also lead to adverse health effects. Vibration caused a drop in WSS power for the frequency band associated with the neurogenic activity of the sympathetic nervous system.

CONCLUSION

This study may pave the way for a new framework to prevent vibration-induced vascular risk.

Afferent volley from the digital nerve induces short-latency facilitation of perceptual sensitivity and primary sensory cortex excitability

The present study examined whether the perceptual sensitivity and excitability of the primary sensory cortex are modulated by the afferent volley from the digital nerve of a conditioned finger within a short period of time. The perceptual threshold of an electrical stimulus to the index finger (test stimulus) was decreased by a conditioning stimulus to the index finger 4 or 6 ms before the test stimulus, or by a stimulus to the middle or ring finger 2 ms before that. This is explained by the view that the afferent volleys from the digital nerves of the fingers converge in the somatosensory areas, causing spatial summation of the afferent inputs through a small number of synaptic relays, leading to the facilitation of perceptual sensitivity. The N20 component of the somatosensory-evoked potential was facilitated by a conditioning stimulus to the middle finger 4 ms before a test stimulus or to the thumb 2 ms before the test stimulus. This is explained by the view that the afferent volley from the digital nerve of the finger adjacent to the tested finger induces lateral facilitation of the representation of the tested finger in the primary sensory cortex through a small number of synaptic relays.

Assessment of thermotactile and vibrotactile thresholds for detecting sensorineural components of the hand-arm vibration syndrome (HAVS)

BACKGROUND

Thermotactile thresholds and vibrotactile thresholds are measured to assist the diagnosis of the sensorineural component of the hand-arm vibration syndrome (HAVS).

OBJECTIVES

This study investigates whether thermotactile and vibrotactile thresholds distinguish between fingers with and without numbness and tingling.

METHODS

In 60 males reporting symptoms of the hand-arm vibration syndrome, thermotactile thresholds for detecting hot and cold temperatures and vibrotactile thresholds at 31.5 and 125 Hz were measured on the index and little fingers of both hands.

RESULTS

In fingers reported to suffer numbness or tingling, hot thresholds increased, cold thresholds decreased, and vibrotactile thresholds at both 31.5 and 125 Hz increased. With sensorineural symptoms on all three phalanges (i.e. numbness or tingling scores of 6), both thermotactile thresholds and both vibrotactile thresholds had sensitivities greater than 80% and specificities around 90%, with areas under the receiver operating characteristic curves around 0.9. There were correlations between all four thresholds, but cold thresholds had greater sensitivity and greater specificity on fingers with numbness or tingling on only the distal phalanx (i.e. numbness or tingling scores of 1) suggesting cold thresholds provide better indications of early sensorineural disorder.

CONCLUSIONS

Thermotactile thresholds and vibrotactile thresholds can provide useful indications of sensorineural function in patients reporting symptoms of the sensorineural component of HAVS.

Graphical message transmission using the monotonic vibration function of a smart phone

This study aimed at evaluating four vibrotactile capabilities for perceiving graphical information presented on a smart phone. Thirty-two blindfolded college students participated in four experiments to test their capabilities of two-point discrimination, relative and absolute judgments of line thickness, and recognition of basic shapes. All the information was received through the default vibration function of the phone, sensed by their scanning fingers. The results showed a good two-point discrimination accuracy rate, reaching 98.8% when the distance between two points was set at 3.2 mm; the relative judgment of line thickness reached the level of 78.3% accuracy when the two-line width difference ratio was set at 3%; the absolute judgment reached the level of 78.8% when the participants recognised line thickness from one of two. Overall, especially for the shapes judgment, the information transmitted by the various codes may be quite low. These findings should inspire advanced investigations and provide design guidelines.

PRACTITIONER SUMMARY

This study tested four vibrotactile capabilities for perception of graphical information when solely using the monotonic vibration function of a smart phone. The results show low information transmission. These findings encourage advanced investigations of new coding systems so that relevant mobile applications could be developed to help the visually impaired.

A Novel Device to Evaluate the Vibrotactile Threshold

This paper presents the initial prototype design of a vibrotactile threshold evaluator for the workplace (VTEW), which is portable and configurable in terms of the probe diameter (2–10 mm), applied frequency (1–500 Hz), angle of probe (0–120 deg), and displacement of probe (1–1500 μm), and is operated with a customizable LABVIEW interface. The vibrotactile threshold is the minimum amplitude of vibration that is perceived at a particular frequency by a subject and is analogous to a hearing test. It can be used to evaluate neuropathy, for instance due to carpal tunnel syndrome or peripheral neuropathy secondary to diabetes. The vibrotactile threshold (VT) at 50 Hz was evaluated using VTEW and an established device, the Vibrotactile Tester (VTT). These results were compared for validation of VTEW. Each subject underwent Phalen’s and Tinel’s test, and the results of these clinical evaluations for carpal tunnel syndrome were used to classify subjects as symptomatic and asymptomatic. The results of the VTEW and the VTT were statistically similar and the age correction developed for both devices from this study were similar to the previously conducted studies. The mean VT values from the VTEW showed an increased VT for symptomatic subjects. The low frequency range of the VTEW was used to evaluate the VT at 4 Hz, and a comparison of VT at 4 Hz and 50 Hz showed a higher sensitivity of subjects to 50 Hz as compared to 4 Hz. The gender effect on VT was also studied and discussed, along with recommendation for further investigation. A novel and highly customizable device for testing the vibrotactile threshold is presented, with results demonstrating identification of symptomatic subjects. This device could be used to regularly test workers at risk for developing carpal tunnel syndrome (e.g. assembly line workers) to monitor for elevations in VT. Other applications include using the low frequency to evaluate peripheral neuropathy.

Progress in vibrotactile threshold evaluation techniques: a review

Vibrotactile threshold (VT) testing has been used for nearly a century to investigate activation of human somatosensory pathways. This use of vibrotactile stimuli provides a versatile tool for detecting peripheral neuropathies, and has been broadly used for investigation of carpal tunnel syndrome. New applications include investigation of drug-induced neuropathies and diabetes-related neuropathies. As a feedback device, the vibrotactile stimuli could be used as an information delivery system for rehabilitative feedback devices for upper limb musculoskeletal disorders or as information channels for the visually impaired. This review provides a comprehensive review of the advancement in VT measurement techniques over time and a comparison of these techniques in terms of various hardware features used and the testing protocols implemented. The advantages and limitations of these methods have been discussed along with specific recommendations for their implementation and suggestions for incorporation into clinical practice.

Reductions in finger blood flow in men and women induced by 125-Hz vibration: association with vibration perception thresholds

Vibration of one hand reduces blood flow in the exposed hand and in the contralateral hand not exposed to vibration, but the mechanisms involved are not understood. This study investigated whether vibration-induced reductions in finger blood flow are associated with vibrotactile perception thresholds mediated by the Pacinian channel and considered sex differences in both vibration thresholds and vibration-induced changes in digital circulation. With force and vibration applied to the thenar eminence of the right hand, finger blood flow and finger skin temperature were measured in the middle fingers of both hands at 30-s intervals during seven successive 4-min periods: 1) pre-exposure with no force or vibration, 2) pre-exposure with force, 3) vibration 1, 4) rest with force, 5) vibration 2, 6) postexposure with force, and 7) recovery with no force or vibration. A 2-N force was applied during periods 2-6 and 125-Hz vibration at 0.5 and 1.5 ms(-2) root mean square (r.m.s.; unweighted) was applied during periods 3 and 5, respectively. Vibrotactile thresholds were measured at the thenar eminence of right hand using the same force, contact conditions, and vibration frequency. When the vibration magnitude was greater than individual vibration thresholds, changes in finger blood flow were correlated with thresholds (with both 0.5 and 1.5 ms(-2) r.m.s. vibration): subjects with lower thresholds showed greater reductions in finger blood flow. Women had lower vibrotactile thresholds and showed greater vibration-induced reductions in finger blood flow. It is concluded that mechanoreceptors responsible for mediating vibration perception are involved in the vascular response to vibration.

Normal values for thermotactile and vibrotactile thresholds in males and females

OBJECTIVES

This study was undertaken to compare normal values of thermotactile and vibrotactile thresholds in males and females and in younger and older age groups. In addition, for thermal thresholds, the effects of the contact area (small and large) and stimulus location (glabrous and non-glabrous skin) were investigated.

METHOD

Eighty healthy subjects participated in the study: 20 males and 20 females aged 20-30 years, and 20 males and 20 females aged 55-65 years. Subjects attended one 45 min experimental session consisting of acclimatisation for 10 min followed by 35 min of testing. Using the method of limits, hot thresholds and cold thresholds were measured on the non-dominant upper limb at three locations (the distal phalanx of the middle finger, the thenar eminence, and the dorsal surface of the forearm) using two circular contactors 1.0 and 2.8 cm in diameter. Using the von Békésy method, vibrotactile thresholds at 31.5 and 125 Hz were measured on the distal phalanx of the middle finger of the non-dominant hand.

RESULTS

Among the younger subjects there were significant gender differences in thermotactile thresholds but not vibrotactile thresholds. Age did not have any significant effect on thermotactile or vibrotactile thresholds. Hot thresholds were significantly higher and cold thresholds significantly lower when the larger stimulus area was used. The thresholds exceeded by 18% of the population (the mean plus one standard deviation) and by 2.5% (the mean plus two standard deviations) are provided and may be used to consider whether measured thresholds are within a "normal" range.

CONCLUSIONS

For males and females the same ranges of normal values may be used for vibrotactile thresholds but different ranges of normal values may be required for thermotactile thresholds. An age correction may not be needed for thermotactile or vibrotactile thresholds in persons aged 20-65 years. Contact area has an influence on thermotactile thresholds and should be controlled.