Acute effects of mechanical shocks on finger blood flow: influenceof 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.