Response of finger circulation to energy equivalent combinations of magnitude and duration of vibration

Objectives-To investigate the acute response of finger circulation to vibra tion with different combinations of magnitude and duration but with the sam e "energy equivalent" acceleration magnitude according to current standards for hand transmitted vibration. Methods-Finger skin temperature (FST) and finger blood flow (FBF) were meas ured in the middle fingers of both hands of 10 healthy men who had not used hand held vibrating tools regularly. With a static load of 10 N, the right hand was exposed to 125 Hz vibration with the following unweighted root me an square (rms) acceleration magnitudes and durations of exposure: 44 m/s(2 ) for 30 minutes; 62 m/s(2) for 15 minutes; 88 m/s(2) for 7.5 minutes; 125 m/s(2) for 3.75 minutes; and 176 m/s(2) for 1.88 minutes. These vibration e xposures produce the same 8 hour energy equivalent frequency weighted accel eration magnitude (similar to1.4 m/s(2) rms) according to international sta ndard ISO 5349 (1986). Finger circulation was measured in both the right (v ibrated) and the left (non-vibrated) middle fingers before application of t he vibration, and at fixed intervals during exposure to vibration and durin g a 45 minute recovery period. Results-The FST did not change during exposure to vibration, whereas vibrat ion with any combination of acceleration magnitude and duration produced si gnificant percentage reductions in the FBF of the vibrated finger compared with the FBF before exposure (from -40.1% (95% confidence interval (95% CI) -24.3% to -57.2%) to -61.4% (95% CI -45.0% to -77.8%). The reduction in FB F during vibration was stronger in the vibrated finger than in the non-vibr ated finger. Across the five experimental conditions, the various vibration stimuli caused a similar degree of vasoconstriction in the vibrated finger during exposure to vibration. There was a progressive decrease in the FBF of both fingers after the end of exposure to vibration with acceleration ma gnitudes of 44 m/s(2) for 30 minutes and 62 m/s(2) for 15 minutes. Signific ant vasoconstrictor after effects were not found in either finger after exp osure to any of the other vibration stimuli with greater acceleration magni tudes for shorter durations. Conclusions-For the range of vibration magnitudes investigated (44 to 176 m /s(2) rms unweighted; 5.5 to 22 m/s(2) rms when frequency weighted accordin g to ISO 5349), the vasoconstriction during exposure to 125 Hz vibration wa s independent of vibration magnitude. The after effect of vibration was dif ferent for stimuli with the same energy equivalent acceleration, with great er effects after longer durations of exposure. The energy equivalent accele ration therefore failed to predict the acute effects of vibration both duri ng and after exposure to vibration. Both central and local vasoregulatory m echanisms are likely to be involved in the response of finger circulation t o acute exposures to 125 Hz vibration.