Acute effects of force and vibration on finger blood flow

Objectives: To investigate the effects of contact force at the finger on acute changes in finger circulation during exposure to vibration. Methods: Each of 10 subjects attended 11 sessions in which they experienced five successive experimental 5-minute periods: (i) no force and no vibration; (ii) force and no vibration; (iii) force and vibration; (iv) force and no vibration; (v) no force and no vibration. During periods (ii) to (iv), the intermediate phalanx of the right middle finger applied one of two forces (2 N or 5 N) on a platform that vibrated during period (iii) at one of two frequencies: 31.5 Hz (at 4 or 16 ms22 r.m.s.) or 125 Hz (at 16 or 64 ms22 r.m.s.). Finger blood flow was measured in the exposed right middle finger, the unexposed right little finger, and the unexposed left middle fingers throughout the 25 minutes of each session. Results: The application of force alone caused a reduction in finger blood flow in the exposed finger, but not other fingers. There were additional reductions in finger blood flow caused by vibration, with greater reductions at the higher vibration magnitudes at both frequencies but no difference between the two frequencies when using unweighted acceleration. The vibration caused a similar vasoconstriction in vibrated and non-vibrated fingers. Conclusions: Modest levels of force applied by a finger can have a large effect on the finger blood flow, possibly due to the constriction of local blood vessels. The acute vascular effects of vibration cause additional reductions in finger blood flow that are not limited to the finger experiencing force and vibration. In all fingers (exposed and not exposed to vibration), the greater the magnitude of vibration, the greater the reduction in finger blood flow. In all fingers (exposed and not exposed to vibration), when the vibration was frequency weighted according to current standards, 125 Hz vibration caused greater reductions in finger blood flow than 31.5 Hz vibration.