Sensory perception testing by monofilaments in the digits of controls and workers with HAVS

Applied Force Alters Sensorineural and Peripheral Vascular Function in a Rat Model of Hand-Arm Vibration Syndrome

OBJECTIVE

This study described the effects of applied force (grip) on vascular and sensorineural function in an animal model of hand-arm vibration syndrome (HAVS).

METHODS

Rat tails were exposed to 0, 2, or 4 N of applied force 4 hr/d for 10 days. Blood flow and sensitivity to transcutaneous electrical stimulation and pressure were measured.

RESULTS

Applied force increased blood flow but reduced measures of arterial plasticity. Animals exposed to force tended to be more sensitive to 250-Hz electrical stimulation and pressure applied to the tail.

CONCLUSIONS

Effects of applied force on blood flow and sensation are different than those of vibration. Studies examining co-exposures to force and vibration will provide data that can be used to determine how these factors affect risk of workers developing vascular and sensorineural dysfunction (ie, HAVS).

On the mechanics of monofilaments used in touch sensory perception

The buckling of a slender monofilament is a standard clinical method used to assess touch sensory perception, with specific applications to somatosensory impairment in patients after a stroke, detecting carpal tunnel syndrome, and as a prognosis tool for diabetic peripheral neuropathy. The basis of this approach is the Semmes-Weinstein monofilament, which comprises a calibrated set of thin, polycarbonate rods with different diameters. Application of a monofilament onto the surface of the skin with increasing pressure causes the rod to buckle. That is, at a specific force of pushing down on the far end, the monofilament suddenly bows out sidewards - the buckling load. The ability of a patient to detect increasingly finer monofilament buckling (pressure threshold) is then used to assess sensory deterioration. This paper addresses the underlying mechanics of the buckling process. Despite the accuracy and repeatability problems that have been reported in the literature, and the necessarily subjective aspects of sensory physiology, the mathematical modeling of the monofilament buckling is unambiguous and provides some fundamental insight into the parameters that underlie this approach.

Concordance between the Stockholm Workshop Scale and the International Consensus Criteria for grading the severity of neurosensory manifestations in hand-arm vibration syndrome in a Swedish clinical setting

OBJECTIVES

Occupational exposure to vibration using hand-held tools may cause hand-arm vibration syndrome (HAVS). Correct diagnosis and grading of severity are crucial in protecting the individual's health and for workers' compensation claims. The International Consensus Criteria (ICC) has been suggested to replace the widely used Stockholm Workshop Scale (SWS). The aims were to, in a clinical setting, assess the concordance between the SWS and the ICC neurosensory severity grading of vibration injury, and to present the clinical picture according to symptoms, type of affected nerve fibres and the relation between vascular and neurosensory manifestations.

METHODS

Data were collected from questionnaires, clinical examination and exposure assessment of 92 patients with HAVS. The severity of neurosensory manifestations was classified according to both scales. The prevalence of symptoms and findings was compared across groups of patients with increasing severity according to the SWS.

RESULTS

Classification with the ICC resulted in a shift towards lower grades of severity than with the SWS due to a systematic difference between the scales. Affected sensory units with small nerve fibres were far more prevalent than affected units with large nerve fibres. The most prevalent symptoms were numbness (91%) and cold intolerance (86%).

CONCLUSIONS

Using the ICC resulted in lower grades of the severity of HAVS. This should be taken into consideration when giving medical advice and approving workers' compensation. Clinical examinations should be performed to detect affected sensory units with both small and large nerve fibres and more attention should be paid to cold intolerance.

A Review of Hand-Arm Vibration Studies Conducted by US NIOSH since 2000

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.