Effect of the magnitude and frequency of hand-transmitted vibration on finger blood flow during and after exposure to vibration

Finger blood flow (FBF) measurement among vibration-exposed groundskeepers: a pilot study in the southeastern USA

OBJECTIVES

This study assessed finger blood flow (FBF) among groundskeepers using laser Doppler flowmetry (LDF) and evaluated the association of the FBF with hand-arm vibration (HAV) exposure dose.

METHODS

Baseline FBF measured before a work shift (FBFbaseline) and daily changes in FBF before and after a work shift (ΔFBFdaily) were measured among 17 groundskeepers and 10 office workers using LDF (PeriFlux 6000, Perimed, Järfälla, Sweden) for 3 days. Study participants' health-related information was obtained through questionnaires, while HAV exposure and demographic information were pulled from our previous study conducted in parallel with the present study. Linear mixed models were employed to estimate the association between HAV exposure dose and FBF.

RESULTS

The average FBFbaseline for right and left hands was 241.5 and 239.9 perfusion units (PUs), respectively, among the exposure group and 305.6 and 307.3 PU, respectively, among the reference group. The average ΔFBFdaily for right and left hands was 44.2 and 25.4 PU, respectively, among the exposure group and -35.2 and -33.2 PU, respectively, among the reference group. A significant negative association between lifetime HAV exposure and FBFbaseline was observed in the linear mixed model after adjusting for age, body mass index, race/ethnicity and hypertension (right hand: β=-0.0006 and p=0.0055; left hand: β=-0.0009 and p=0.0068). Inconsistent significances were observed between lifetime HAV exposure and ΔFBFdaily and between daily HAV exposure and ΔFBFdaily.

CONCLUSIONS

A significant negative association between lifetime HAV exposure and baseline FBF among groundskeepers was observed, supporting FBF measurement using LDF as a promising health indicator for vascular disorders induced by HAV.

Force-induced tissue compression alters circulating hormone levels and biomarkers of peripheral vascular and sensorineural dysfunction in an animal model of hand-arm vibration syndrome

Workers regularly using vibrating hand tools may develop a disorder referred to as hand-arm vibration syndrome (HAVS). HAVS is characterized by cold-induced vasospasms in the hands and fingers that result in blanching of the skin, loss of sensory function, pain, and reductions in manual dexterity. Exposure to vibration induces some of these symptoms. However, the soft tissues of the hands and fingers of workers are compressed as a result of the force generated when a worker grips a tool. The compression of these soft tissues might also contribute to the development of HAVS. The goal of this study was to use an established rat tail model to determine the mechanisms by which compression of the tail tissues affects (1) the ventral tail artery (VTA) and ventral tail nerves (VTN), (2) nerves and sensory receptors in the skin, (3) dorsal root ganglia (DRG), and (4) spinal cord. Tissue compression resulted in the following changes (1) circulating pituitary and steroid hormone concentrations, (2) expression of factors that modulate vascular function in the skin and tail artery, and (3) factors associated with nerve damage, DRG, and spinal cord. Some of these observed effects differed from those previously noted with vibration exposure. Based upon these findings, the effects of applied force and vibration are different. Studies examining the combination of these factors might provide data that may potentially be used to improve risk assessment and support revision of standards.

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.

Vascular response to the microcirculation in the fingertip by local vibration with varied amplitude

Objectives: We investigated the effect of local vibration intensity on the vascular response to the microcirculation of the finger. Materials and methods: We performed hand-transmitted vibration experiments combined with laser Doppler flowmetry (LDF) to measure the blood perfusion signals of fingertips in the vibrated hand and the contralateral middle finger under the same frequency and different amplitude vibration, and to analyze the changes of microcirculatory blood perfusion levels in the fingers, and to investigate the effects of vibration stimulation on the endothelial, neural and myogenic regulatory frequency ranges of fingertips based on wavelet analysis. Furthermore, the transparent silicone films were fabricated and cultured with vascular endothelial cell (EC), which will undergo the local vibration with varied amplitude. And the expression of inflammatory factors was detected in the ECs. Results: Low-frequency vibration leads to a decreased blood flow in fingertip, and the degree of reduction in fingertip blood flow increases as the amplitude gradually increases, and the period required for blood flow to return to normal level after hand-transmitted vibration gradually increases. The decrease in blood flow is more pronounced in the vibrating hand than in the contralateral hand. In addition, nuclear factor-κB (NF-κB) expression increased significantly with the increase of vibration amplitude. Conclusion: High amplitude vibrations caused the inflammatory reaction of ECs which will lead to the altered endothelial regulatory activity. The endothelial regulatory activity is closely related to the blood perfusion in the microcirculation.

Acute physiological and functional effects of repetitive shocks on the hand-arm system - a pilot study on healthy subjects

PURPOSE

Exposure to hand-transmitted shocks is a widespread phenomenon at the workplace. Separate risk assessments for shocks do not exist in current international hand-arm vibration regulations, leading to a potential underestimation of associated health risks.

METHODS

In a pilot study approach, N = 8 healthy males were exposed to sets of 3×5 minutes of repetitive shocks and 1×5 minutes of random vibration, controlled at a weighted vibration total value of 10 m/s² respectively. Baseline and post-exposure measurements of vibration perception thresholds, finger skin temperature, maximal grip / pinch force and the Purdue Pegboard test were conducted. Muscle activity was monitored continuously by surface electromyography.

RESULTS

Shock exposures evoked a temporary increase of vibration perception thresholds with high examination frequencies. A decrease of skin temperature was hinted for 1 s^-1 and 20 s^-1 shocks. Electromyographical findings indicated an additional load on two forearm muscles during shock transmission. Maximum grip force and manual dexterity were not affected, pinch force only partially reduced after the exposures.

CONCLUSION

Physiological effects from shock exposure conform to those described for hand-arm vibration exposure in principle, although some divergence can be hypothesized. Randomized designs are required to conclusively assess the need of occupational health concepts specifically for hand-transmitted shocks.

Acute Vascular Response of Hand to Force and Vibration

This study aimed to investigate the acute effect of grip and feed exertions on the vascular system at the fingers during exposure to hand-arm vibration (HAV), and to identify which active hand force situation would have the most effect on finger vascular function. A total of 12 individuals attended the test, and each of them were subjected to eight sets of force-and-vibration situations: four with combinations of forces and vibration, and four control ones with only hand forces applied. The vibration stimulus was applied on the right hand at 2.75 m/s2 with a frequency of 125 Hz for three minutes, during which the application of grip and feed forces were set at either 10 N or 50 N. The weakening of the finger vascular function was reflected by a reduction in the finger blood flow (FBF) and finger skin temperature (FST). They were tested on both hands at fixed intervals before, during and after the exposure for in-time measurement. Hand forces resulted in clear reductions in FBF and FST in exposed right fingers whether the force was exerted solely or combined with vibration. The greater the hand force (especially grip force), the stronger the vascular response, while the additional reductions in FBF and FST from vibration were not significant. In the non-exposed left fingers, no significant changes in finger circulation occurred in response to force or vibration. Generally, vibration-induced acute finger vasoconstriction was affected by the hand forces, in which hand force seemed to play a more important part than vibration. A larger grip force would lead to a greater loss in the digital circulation than feed force. Thus, the level of hand force exerted on the tool handle should be limited to reduce the risk of harm from HAV.

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.

Vibration-induced injuries in workers exposed to transient and high frequency vibrations

Background

The risk of developing vibration white fingers and neurosensory symptoms increases with the duration and intensity of the exposure. The aim of this study was to investigate the risk of developing vibration white fingers (VWF), neurosensory symptoms and musculoskeletal disorders among workers exposed to transient and high frequency vibrations.

Methods

The study included 38 vibration exposed workers from a loader assembly plant in Sweden (30 males and 8 females). All participants answered questionnaires and had a structured interview about work and medical history. A following medical examination included the determination of vibration and temperature perception thresholds and musculoskeletal symptoms in the neck, shoulder, elbow and hands. The individual vibration exposure expressed as A (8)-values and vibration exposure in minutes per day, were obtained from questionnaires answered by the participants.

Results

The prevalence of VWF was 30% among the male workers and 50% among the females. The corresponding prevalence of neurosensory symptoms was 70% among the males and 88% among the females. Musculoskeletal findings were common among the male workers. Dominant symptoms/syndromes were tension neck syndrome, biceps tendinitis, carpal tunnel syndrome and ulnar entrapment in hand/wrist. A total of 32 diagnoses were observed among the male workers and four diagnoses among the female workers. Numbness in fingers and age had the strongest impact on perceived work ability.

Conclusions

ISO 5349-1 considerably underestimates the risks of VWF for this group of workers exposed to transient and high frequency vibrations. It is therefore important to develop a risk assessment standard also covering this frequency range.

Skin temperature responses to hand-arm vibration in cold and thermoneutral ambient temperatures

Hand-arm vibration (HAV) from hand-held vibrating machines increases the risk of injury in the form of vasoconstriction in the fingers, commonly named as vibration induced white fingers (VWF). Cold temperature may increase that risk. This experimental study examined and compared the effects of the skin temperature of the hands during and after exposure to HAV in thermoneutral and cold conditions. Fourteen subjects were exposed to three conditions: 25°C with HAV, 5°C with HAV or 5°C without HAV. Their skin temperatures were continuously recorded for the thumbs, index fingers, palms, and back of hands. After 20 min of acclimatization, the subjects held, for five min, two handles where the right handle could vibrate at 5 m/s² and the left was stationary. Finally, they released their grip and stood still for 10 more min. HAV had no additional cooling effect in cold during gripping of the handles. After the subjects released the handles there was only a HAV-induced cooling effect in the left palm with on average 0.5°C colder skin temperature. A single exposure to HAV will not cause an injury such as VWF, but as the present study show: short-term exposure to HAV causes some changes in skin temperature.

Risk assessment of vascular disorders by a supplementary hand-arm vascular weighting of hand-transmitted vibration

PURPOSE

To provide an updated epidemiological validation for a supplementary method for assessing the risk of vascular disorders from hand-transmitted vibration.

METHODS

The occurrence of vibration-induced white finger (VWF) in the vibration-exposed workers of the Italian cohort of the EU VIBRISKS study was related to measures of daily vibration exposure expressed in terms of r.m.s. acceleration magnitude normalised to an 8-h day, frequency weighted according to either the frequency weighting W_h defined in international standard ISO 5349-1:2001 [A_h(8) in ms^- 2] or the hand-arm vascular frequency weighting W_p proposed in the ISO technical report (TR) 18570:2017 [A_p(8) in ms^- 2]. To estimate a threshold value for vascular hand-arm vibration risk, the W_p-weighted vibration exposure value E_p,d (in ms^- 1.5) was calculated according to the ISO/TR document. The difference in the predictions of VWF between the exposure measures calculated with the frequency weightings W_h or W_p was investigated by means of logistic modelling.

RESULTS

Measures of daily vibration exposure constructed with the frequency weighting W_p [A_p(8) and E_p,d], which gives more importance to intermediate- and high-frequency vibration, were better predictors of the occurrence of VWF in the vibration-exposed workers than the metric derived from the conventional ISO frequency weighting W_h [A_h(8)]. There was some epidemiological evidence for a threshold value of E_p,d for the onset of VWF in the vibration-exposed workers.

CONCLUSIONS

Measures of daily vibration exposure evaluated with the vascular weighting W_p performed better for the predictions of VWF than those obtained with the frequency weighting W_h recommended in ISO 5349-1.

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

PURPOSE

This study investigated whether the reductions in finger blood flow induced by 125-Hz vibration applied to different locations on the hand depend on thresholds for perceiving vibration at these locations.

METHODS

Subjects attended three sessions during which vibration was applied to the right index finger, the right thenar eminence, or the left thenar eminence. Absolute thresholds for perceiving vibration at these locations were determined. Finger blood flow in the middle finger of both hands was then measured at 30-s intervals during five successive 5-min periods: (i) pre-exposure, (ii) pre-exposure with 2-N force, (iii) 2-N force with vibration, (iv) post-exposure with 2-N force, (v) recovery. During period (iii), vibration was applied at 15 dB above the absolute threshold for perceiving vibration at the right thenar eminence.

RESULTS

Vibration at all three locations reduced finger blood flow on the exposed and unexposed hand, with greater reductions when vibrating the finger. Vibration-induced vasoconstriction was greatest for individuals with low thresholds and locations of excitation with low thresholds.

CONCLUSIONS

Differences in vasoconstriction between subjects and between locations are consistent with the Pacinian channel mediating both absolute thresholds and vibration-induced vasoconstriction.

Relation between vibrotactile perception thresholds and reductions in finger blood flow induced by vibration of the hand at frequencies in the range 8-250 Hz

PURPOSE

This study investigated how the vasoconstriction induced by vibration depends on the frequency of vibration when the vibration magnitude is defined by individual thresholds for perceiving vibration [i.e. sensation levels (SL)].

METHODS

Fourteen healthy subjects attended the laboratory on seven occasions: for six vibration frequencies (8, 16, 31.5, 63, 125, or 250 Hz) and a static control condition. Finger blood flow (FBF) was measured in the middle fingers of both hands at 30-second intervals during five successive periods: (i) no force or vibration, (ii) 2-N force, no vibration, (iii) 2-N force, vibration, (iv) 2-N force, no vibration, (v) no force or vibration. During period (iii), vibration was applied to the right thenar eminence via a 6-mm diameter probe during ten successive 3-min periods as the vibration magnitude increased in ten steps (-10 to +40 dB SL).

RESULTS

With vibration at 63, 125, and 250 Hz, there was vasoconstriction on both hands when the vibration magnitude reached 10 dB SL. With vibration at 8, 16, and 31.5 Hz, there was no significant vasoconstriction until the vibration reached 25 dB SL. At all frequencies, there was greater vasoconstriction with greater magnitudes of vibration.

CONCLUSIONS

It is concluded that at the higher frequencies (63, 125, and 250 Hz), the Pacinian channel mediates vibrotactile sensations near threshold and vasoconstriction occurs when vibration is perceptible. At lower frequencies (8, 16, and 31.5 Hz), the Pacinian channel does not mediate sensations near threshold and vasoconstriction commences at greater magnitudes when the Pacinian channel is activated.

The primary vascular dysregulation syndrome: implications for eye diseases

Vascular dysregulation refers to the regulation of blood flow that is not adapted to the needs of the respective tissue. We distinguish primary vascular dysregulation (PVD, formerly called vasospastic syndrome) and secondary vascular dysregulation (SVD). Subjects with PVD tend to have cold extremities, low blood pressure, reduced feeling of thirst, altered drug sensitivity, increased pain sensitivity, prolonged sleep onset time, altered gene expression in the lymphocytes, signs of oxidative stress, slightly increased endothelin-1 plasma level, low body mass index and often diffuse and fluctuating visual field defects. Coldness, emotional or mechanical stress and starving can provoke symptoms. Virtually all organs, particularly the eye, can be involved. In subjects with PVD, retinal vessels are stiffer and more irregular, and both neurovascular coupling and autoregulation capacity are reduced while retinal venous pressure is often increased. Subjects with PVD have increased risk for normal-tension glaucoma, optic nerve compartment syndrome, central serous choroidopathy, Susac syndrome, retinal artery and vein occlusions and anterior ischaemic neuropathy without atherosclerosis. Further characteristics are their weaker blood–brain and blood-retinal barriers and the higher prevalence of optic disc haemorrhages and activated astrocytes. Subjects with PVD tend to suffer more often from tinnitus, muscle cramps, migraine with aura and silent myocardial ischaemic and are at greater risk for altitude sickness. While the main cause of vascular dysregulation is vascular endotheliopathy, dysfunction of the autonomic nervous system is also involved. In contrast, SVD occurs in the context of other diseases such as multiple sclerosis, retrobulbar neuritis, rheumatoid arthritis, fibromyalgia and giant cell arteritis. Taking into consideration the high prevalence of PVD in the population and potentially linked pathologies, in the current article, the authors provide recommendations on how to effectively promote the field in order to create innovative diagnostic tools to predict the pathology and develop more efficient treatment approaches tailored to the person.

Association between vasoconstriction during and following exposure to hand-transmitted vibration

OBJECTIVES

This study investigated whether reductions in finger blood flow (FBF) during and after vibration are similarly dependent on the magnitude and duration of the vibration.

METHODS

FBF on the left and right hand was measured every minute during, and for 1 h following, exposure of the right hand to one of three magnitudes of 125-Hz sinusoidal vibration (0, 22, or 88 ms(-2) rms) for one of two durations (7.5 or 15 min). Each of five experimental sessions was comprised of five periods: (i) no force and no vibration (5 min), (ii) 2-N force and no vibration (5 min), (iii) 2-N force and vibration (7.5 or 15 min), (iv) 2-N force and no vibration (5 min), and (v) no force and no vibration (60 min).

RESULTS

Vibration reduced FBF in the exposed and unexposed hands, both during and after vibration. With increased magnitude of vibration, there was increased vasoconstriction in all fingers during and after exposure, and longer recovery times after vibration exposure. With increased duration of vibration, there were no changes in vascular responses during exposure but increased vasoconstriction after exposure and prolonged recovery times. With the greater vibration magnitude, the reduction in FBF during exposure was correlated with the time taken to recover after exposure.

CONCLUSIONS

Subjects with greater reduction in blood flow during vibration exposure also have stronger and longer vasoconstriction during subsequent recovery. The correlation between vascular changes during and after vibration exposure suggests similar mechanisms control FBF during and after vibration exposure.

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.

Acute effects of mechanical shocks on finger blood flow: influence of shock repetition rate and shock magnitude

OBJECTIVES

Finger blood flow is reduced by hand-transmitted vibration but there has been little study of the peripheral vascular response to repetitive mechanical shocks. This study investigated how reductions in finger blood flow depend on shock repetition rate and the peak and rms magnitude of acceleration.

METHODS

Subjects attended seven sessions: six with repetitive mechanical shocks and a control session with no shocks. Each session comprised five successive 5-min periods: (1) no force and no vibration, (2) force and no vibration, (3) force and vibration, (4) force and no vibration and (5) no force and no vibration. During the second-fourth periods, the palm of the right hand applied 2-N force to a vibrator. During the third period, a 125-Hz mechanical shock was applied with one of four repetition rates (1.3, 5.3, 21 or 83.3/s) and one of three acceleration magnitudes (2.5, 5 or 10 ms(-2) rms, unweighted). Finger blood flow was measured every 30 s in the middle and little fingers of the right (exposed) hand and the left (unexposed) hand.

RESULTS

Different repetition rates (1.3-83.3 s(-1)) and different peak magnitudes (10-88 ms(-2) peak) but the same rms acceleration (10 ms(-2) rms) caused similar decreases in blood flow in fingers on exposed and unexposed hands. Shocks with a 83.3 s(-1) repetition rate, peak magnitude of 10 ms(-2) and rms acceleration of 10 ms(-2) provoked greater reduction in finger blood flow than shocks with the same peak magnitude but lower repetition rate (21 or 5.3 s(-1)) and lower rms acceleration (5 or 2.5 ms(-2)).

CONCLUSIONS

For shocks similar to those based on 125-Hz oscillations with repetition rates between 1.3 and 83.3 s(-1), acute reductions in finger blood flow can be predicted from the rms acceleration.

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.

Effects of temperature on reductions in finger blood flow induced by vibration

PURPOSE

To investigate how temperature influences changes in finger circulation induced by hand-transmitted vibration in healthy subjects, and the variability in individual response to both vibration and temperature.

METHODS

With two room temperatures (20 and 28°C), finger blood flow (FBF) and finger skin temperature (FST) were measured on the left middle fingers of 12 subjects at 1-min intervals during three successive 10-min periods. A 5-N static force was applied throughout the 30-min period, and sinusoidal 125-Hz vibration at 44 ms(-2) rms. (unweighted) was applied to the right hand during the second of the three 10-min periods.

RESULTS

Before exposure to vibration, both FBF and FST were greater with the higher room temperature. Finger blood flow in the left hand reduced during vibration of the right hand. The reduction in absolute FBF differed between the two room temperatures, but the percentage reduction in FBF relative to FBF before exposure to vibration was similar. After cessation of vibration, there was continued reduction in FBF with both room temperatures. Before and after vibration exposure, the FST was correlated with FBF and the FBF and FST at 20°C were correlated with the FBF and FST at 28°C.

CONCLUSIONS

Vibration of one hand can reduce finger blood flow and skin temperature on the unexposed hand, with the reduction dependent on temperature. The absolute reduction in FBF was greater with the higher room temperature, but the percentage reduction in FBF relative to FBF before vibration exposure was similar. Those with greater finger blood flow before vibration tend to have greater blood flow during vibration, and those with greater finger blood flow with one temperature tend to have greater blood flow with another temperature.