Cardiovascular responses to autonomic stimuli in workers with vibration-induced white finger

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.

Systemic Effects of Segmental Vibration in an Animal Model of Hand-Arm Vibration Syndrome

OBJECTIVE

Epidemiology suggests that occupational exposure to hand-transmitted (segmental) vibration has local and systemic effects. This study used an animal model of segmental vibration to characterize the systemic effects of vibration.

METHODS

Male Sprague Dawley rats were exposed to tail vibration for 10 days. Genes indicative of inflammation, oxidative stress, and cell cycle, along were measured in the heart, kidney, prostate, and liver.

RESULTS

Vibration increased oxidative stress and pro-inflammatory gene expression, and decreased anti-oxidant enzymes in heart tissue. In the prostate and liver, vibration resulted in changes in the expression of pro-inflammatory factors and genes involved in cell cycle regulation.

CONCLUSIONS

These changes are consistent with epidemiological studies suggesting that segmental vibration has systemic effects. These effects may be mediated by changes in autonomic nervous system function, and/or inflammation and oxidative stress.

Modeling of the interaction between grip force and vibration transmissibility of a finger

It is known that the vibration characteristics of the fingers and hand and the level of grip action interacts when operating a power tool. In the current study, we developed a hybrid finger model to simulate the vibrations of the hand-finger system when gripping a vibrating handle covered with soft materials. The hybrid finger model combines the characteristics of conventional finite element (FE) models, multi-body musculoskeletal models, and lumped mass models. The distal, middle, and proximal finger segments were constructed using FE models, the finger segments were connected via three flexible joint linkages (i.e., distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP), and metacarpophalangeal (MCP) joint), and the MCP joint was connected to the ground and handle via lumped parameter elements. The effects of the active muscle forces were accounted for via the joint moments. The bone, nail, and hard connective tissues were assumed to be linearly elastic whereas the soft tissues, which include the skin and subcutaneous tissues, were considered as hyperelastic and viscoelastic. The general trends of the model predictions agree well with the previous experimental measurements in that the resonant frequency increased from proximal to the middle and to the distal finger segments for the same grip force, that the resonant frequency tends to increase with increasing grip force for the same finger segment, especially for the distal segment, and that the magnitude of vibration transmissibility tends to increase with increasing grip force, especially for the proximal segment. The advantage of the proposed model over the traditional vibration models is that it can predict the local vibration behavior of the finger to a tissue level, while taking into account the effects of the active musculoskeletal force, the effects of the contact conditions on vibrations, the global vibration characteristics.

Assessment of two alternative standardised tests for the vascular component of the hand-arm vibration syndrome (HAVS)

Background

Vibration-induced white finger (VWF) is the vascular component of the hand–arm vibration syndrome (HAVS). Two tests have been standardised so as to assist the diagnosis of VWF: the measurement of finger rewarming times and the measurement of finger systolic blood pressures (FSBPs).

Objectives

This study investigates whether the two tests distinguish between fingers with and without symptoms of whiteness and compares individual results between the two test methods.

Methods

In 60 men reporting symptoms of the HAVS, the times for their fingers to rewarm by 4°C (after immersion in 15°C water for 5 min) and FSBPs at 30°C, 15°C and 10°C were measured on the same day.

Results

There were significant increases in finger rewarming times and significant reductions in FSBPs at both 15°C and 10°C in fingers reported to suffer blanching. The FSBPs had sensitivities and specificities >90%, whereas the finger rewarming test had a sensitivity of 77% and a specificity of 79%. Fingers having longer rewarming times had lower FSBPs at both temperatures.

Conclusions

The findings suggest that, when the test conditions are controlled according to the relevant standard, finger rewarming times and FSBPs can provide useful information for the diagnosis of VWF, although FSBPs are more sensitive and more specific.

Reductions in finger blood flow induced by 125-Hz vibration: effect of area of contact with vibration

To investigate whether the Pacinian channel is involved in vibration-induced reductions of finger blood flow (FBF), vibrotactile thresholds and vasoconstriction have been studied with 125-Hz vibration and two contact areas: 3- or 6-mm-diameter vibrating probes with 2-mm gaps to fixed surrounds. Fifteen subjects provided thresholds for perceiving vibration at the thenar eminence of the right hand with both contact areas. With both contact areas, FBF was then measured in the middle fingers of both hands during five successive 5-min periods: (i) no force and no vibration, (ii) force and no vibration, (iii) force with vibration 15 dB above threshold, (iv) force and no vibration, and (v) no force and no vibration. Thresholds were in the ranges of 0.16-0.66 ms(-2) r.m.s. (6-mm probe) and 0.32-1.62 ms(-2) r.m.s. (3-mm probe). With the magnitude of vibration 15 dB above each individual's threshold with the 3-mm probe, the median reduction in FBF with the 6-mm probe (to 70 and 77 % of pre-exposure FBF on the exposed right hand and the unexposed left hand, respectively) was greater than with the 3-mm probe (79 and 85 %). There were similar reductions in FBF when vibration was presented by the two contactors at the same sensation level (i.e. 15 dB above threshold with each probe). The findings are consistent with reductions in FBF arising from excitation of the Pacinian channel: increasing the area excited by vibration increases Pacinian activation and provokes stronger perception of vibration and greater vasoconstriction.

Test battery for assessing vascular disturbances of fingers

The diagnosis of vibration-induced white finger (VWF) is difficult, often relying on medical interview and history. The condition is characterized by an exaggerated vasoconstriction of digital arteries in response to cold. The complete closure of digital arteries is episodic and results in a characteristic blanching that is rarely observed by a clinician. Objective measurements of the response of the digital circulation to cold can assist in evaluating a patient for VWF. Finger systolic blood pressure (FSBP) following local cooling is a measure of cold-induced vasoconstriction in digital arteries and is an assessment of vasomotor tone. Low FSBPs following cooling are indicative of dysfunction. Finger skin temperature (FST) following hand cooling is a measure of cutaneous blood flow. The mechanism underlying the recovery of cutaneous blood flow following cooling is as yet not fully understood, but a delayed recovery is believed to arise from persistent vascular disturbances of the fingers or from a resulting in conflicting opinions concerning the utility of the measurements, a scarcity of comparable data from epidemiological investigations, and limited normative data to aid clinicians in decision-making. This review of evidence on which the tests are based is aimed at providing clinicians and researchers with an understanding of the factors that must be considered when conducting the tests, interpreting the results, and comparing results between different studies.

Dynamic interaction between a fingerpad and a flat surface: experiments and analysis

Many neural and vascular diseases in hands and fingers have been related to the degenerative responses of local neural and vascular systems in fingers to excessive dynamic loading. Since fingerpads serve as a coupling element between the hand and the objects, the investigation of the dynamic coupling between fingertip and subjects could provide important information for the understanding of the pathomechanics of these neural and vascular diseases. In the present study, the nonlinear and time-dependent force responses of fingertips during dynamic contact have been investigated experimentally and theoretically. Four subjects (2 male and 2 female) with an average age of 24 years participated in the study. The index fingers of right and left hands of each subject were compressed using a flat platen via a micro testing machine. A physical model was proposed to simulate the nonlinear and time-dependent force responses of fingertips during dynamic contact. Using a force relaxation test and a fast loading test at constant loading speed, the material/structural parameters underlying the proposed physical model could be identified. The predicted rate-dependent force/displacement curves and time-histories of force responses of fingertips were compared with those measured in the corresponding experiments. Our results suggest that the force responses of fingertips during the dynamic contacts are nonlinear and time-dependent. The physical model was verified to characterize the nonlinear, rate-dependent force-displacement behaviors, force relaxations, and time-histories of force responses of fingertips during dynamic contact.

Factors influencing autonomic nervous function during cold-water immersion test in patients with hand-arm vibration syndrome

OBJECTIVES

Factors influencing autonomic nervous function in patients with hand-arm vibration syndrome (HAVS) in response to cold-water immersion test with different water temperatures and immersion times were investigated in the summer and winter seasons.

METHODS

Fourteen HAVS patients with vibration-induced white finger (VWF) and 14 healthy control subjects individually age-matched to the patients consented in writing and participated in this study. Patients and controls immersed their left hands in water at 10 degrees C for 10 min and at 15 degrees C for 3 min in summer and in winter in a room with temperature maintained at 21+/-1 degrees C. Electrocardiographic (ECG) data were recorded during the test period and the R-R intervals were analyzed with a fast Fourier transformation (FFT) program. Percentage of very low frequency (VLF%; indicator of both sympathetic and parasympathetic nervous function, and function of rennin-angiotensin system), low frequency (LF%; indicator of both sympathetic and parasympathetic nervous function), high frequency (HF%; indicator of parasympathetic nervous function), and LF/HF ratio (indicator of sympathetic nervous function) were calculated. The results by three-way analysis of variance (ANOVA) were reported elsewhere. In the present study, repeated measures ANOVA was used to re-analyze the factors of data measurement time (time factor) and group (group factor), and their interaction for each test method (water at 10 degrees C for 10-min immersion time; water at 15 degrees C for 3-min immersion time) in summer and winter.

RESULTS

The HF% of HAVS patients tended to be lower than that of healthy controls throughout the cold-water immersion tests except for during tests involving water at 10 degrees C for 10-min immersion in summer. The group factor for HF% was statistically significant with an exception during the test involving water at 10 degrees C and 10-min immersion time in summer. The time factor for HF% was statistically significant with an exception during the test involving water at 15 degrees C and 3-min immersion time in winter.

CONCLUSIONS

The findings of the present study indicated lower cardiac parasympathetic activity in HAVS patients than in healthy controls, especially in winter. The response of the autonomic nervous system to cold stimulation was to some extent more clearly observed during the immersion test with water at 10 degrees C and 10-min immersion time than during the immersion test with water at 15 degrees C and 3-min immersion time. The results revealed by three-way analysis in a previous study were similar to those in the present study with data analysis by repeated measures ANOVA.

Haemodynamic changes in ipsilateral and contralateral fingers caused by acute exposures to hand transmitted vibration

OBJECTIVES

To investigate changes in digital circulation during and after exposure to hand transmitted vibration. By studying two frequencies and two magnitudes of vibration, to investigate the extent to which haemodynamic changes depend on the vibration frequency, the vibration acceleration, and the vibration velocity.

METHODS

Finger skin temperature (FST), finger blood flow (FBF), and finger systolic pressure were measured in the fingers of both hands in eight healthy men. Indices of digital vasomotor tone-such as critical closing pressure and vascular resistance-were estimated by pressure-flow curves obtained with different hand heights. With a static load of 10 N, the right hand was exposed for 30 minutes to each of the following root mean squared (rms) acceleration magnitudes and frequencies of vertical vibration: 22 m.s-2 at 31.5 Hz, 22 m.s-2 at 125 Hz, and 87 m.s-2 at 125 Hz. A control condition consisted of exposure to the static load only. The measures of digital circulation and vasomotor tone were taken before exposure to the vibration and the static load, and at 0, 20, 40, and 60 minutes after the end of each exposure.

RESULTS

Exposure to static load caused no significant changes in FST, FBF, or indices of vasomotor tone in either the vibrated right middle finger or the non-vibrated left middle finger. In both fingers, exposure to vibration of 125 Hz and 22 m.s-2 produced a greater reduction in FBF and a greater increase in vasomotor tone than did vibration of 31.5 Hz and 22 m.s-2. In the vibrated right finger, exposure to vibration of 125 Hz and 87 m.s-2 provoked an immediate vasodilation which was followed by vasoconstriction during recovery. The non-vibrated left finger showed a significant increase in vasomotor tone throughout the 60 minute period after the end of vibration exposure.

CONCLUSIONS

The digital circulatory response to acute vibration depends upon the magnitude and frequency of the vibration stimulus. Vasomotor mechanisms, mediated both centrally and locally, are involved in the reaction of digital vessels to acute vibration. The pattern of the haemodynamic changes in the fingers exposed to the vibration frequencies used in this study do not seem to support the frequency weighting assumed in the current international standard ISO 5349.

Acute effects of vibration on digital circulatory function in healthy men

OBJECTIVES

To investigate the local and central pathophysiological mechanisms involved in the acute effects of unilateral vibration on the digital circulation of healthy men.

METHODS

Finger blood flow (FBF) and finger skin temperature (FST) in thermoneutral conditions, and the percentage change in finger systolic pressure (FSP%) after local cooling from 30 to 10 degrees C were measured in the fingers of both hands in eight men (aged 23-47 years) who were not occupationally exposed to hand transmitted vibration. The right hand was exposed for 30 minutes to sinusoidal vibration with a frequency of 125 Hz and an acceleration of 87.5 m.s-2 rms (root mean square). A control condition consisted of exposure to static load only (10 N) without vibration. The measures of digital circulation were taken before exposure to vibration and static load and at 0, 30, 60, and 90 minutes after the end of each exposure.

RESULTS

Exposure to static load caused no significant changes in FBF, FST, or FSP% in either the test right or the control left finger. Immediately after vibration exposure, there was a temporary increase in FBF in the vibrated right finger, whereas the non-vibrated left finger showed no vasodilation. In both the vibrated and non-vibrated fingers, FBF and FST were significantly reduced during the recovery time. A large variability between subjects was found for FBF and, to a lesser extent, for FST. In the vibrated right hand the decrease in FBF was significantly related to cold induced vaso-constriction in the digital vessels. Such a relation was not found in the non-vibrated left hand.

CONCLUSIONS

The results of this investigation suggest that acute vibration can disturb the function of digital vessels through two different and opposite mechanisms. Vibration seems to produce local vasodilation and to trigger a central sympathetic reflex vasoconstriction that can be recorded in the ipsilateral and the contralateral finger to vibration. Both local and central vasoconstrictor mechanisms are likely to be involved in the responsiveness to cold found in the digital vessels of a vibrated finger.

Raynaud's syndrome, an enigma after 130 years

The recent literature concerning Raynaud's syndrome is reviewed. Raynaud's syndrome is as common as hypertension and diabetes. In spite of its generally benign character, it causes a lot of discomfort to individuals and sickness absenteeism to society, especially in the colder regions of the world. The etiology remains an enigma 130 years after its first description, perhaps even more so than ever before, the many new theories proposed in the literature. Clearly, in a condition where seventy different etiologic theories are advocated, the culprit lesion is obviously missing, or there is not a culprit lesion but an accumulation of conditions having nothing in common but a few symptoms. Moreover a Raynaud attack may result, not from a single event, but from a cascade of events, just as, for example, hemostasis does. Controversy about diagnosis exists all over. For example, how does one make a diagnosis? Patient history has been considered unreliable. A standardized cold test, though highly reproducible in the authors' hands, is far from common property. Raynaud's syndrome is a condition for which thirty-eight therapies have been advocated in the last three years, but the curative answer is still to come.