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

Abstract

Acute exposures of the hand to vibration result in changes in finger blood flow, but it is not clear how the changes depend on the characteristics of the vibration. To determine the effects of the magnitude and frequency of hand-transmitted vibration on finger blood flow in an exposed and a non-exposed hand during and after exposure to vibration. Twelve persons attended seven sessions consisting of five successive 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, third and fourth periods, the palm of the right hand applied a 2-N downward force on a 25-mm diameter convex platform. During the third period, the platform was vibrated at either 16, 31.5, 63, 125, 250, or 315Hz with the vibration magnitude increasing linearly from 0 to 15ms(-2) rms (frequency-weighted) over 30min (0-11ms(-2) rms at 315Hz). Finger blood flow was measured in the middle and little fingers of the right (exposed) hand and the middle finger of the left (unexposed) hand. The application of 2-N force by the palm did not affect finger blood flow on either the exposed hand or the unexposed hand. Blood flow in all three fingers (both exposed and not exposed to vibration) reduced similarly with increasing vibration magnitude, with the greatest reduction to about 40% of finger blood flow before vibration exposure. During vibration at the same frequency-weighted acceleration according to current standards, finger blood flow was dependent on the vibration frequency, with vibration at 125, 250 and 315Hz causing the greatest reductions in finger blood flow. With vibration at 250Hz and 315Hz, frequency-weighted accelerations less than 1.0ms(-2) rms reduced finger blood flow, whereas greater magnitudes were required at the lower frequencies. After the cessation of vibration, finger blood flow in exposed and unexposed fingers also depended on the vibration frequency, with greater vasoconstriction after exposure to the higher frequencies. During exposure to vibration, vasoconstriction in the fingers depends on both the frequency and the magnitude of the vibration. Finger blood flow was reduced by vibration magnitudes much lower than those on many powered hand tools. Vibration of one hand produced a similar vasoconstriction in fingers on the exposed and unexposed hand, suggesting a centrally mediated response. After cessation of vibration, there is continued vasoconstriction that depends on the frequency and magnitude of the prior vibration, with a similar effect in exposed and non-exposed hands.