Wavelet analysis of acute effects of static magnetic field on resting skin blood flow at the nail wall in young men.

Whether static magnetic field (SMF) can affect microcirculation and microvasculature in human is still ambiguous. In this study, laser Doppler flowmetry (LDF) combined with spectral analysis by wavelet transform was applied to investigate acute SMF-related effects on resting skin blood flow (SBF) at the nail walls. 18 healthy young male volunteers were randomly categorized into two groups: (1) intervention group (INT; n=9) and (2) control group (CTL; n=9). In each group, three 30-minute intervals (pre-exposure, exposure and post-exposure intervals) of continuous LDF recording were taken to evaluate the baseline, SMF effects and its deferred effects. During the exposure interval in the INT group, a neodymium-iron-boron magnet was laid under the middle finger prominence while a sham was used in the CTL group. The effective flux density range of SMF along the axis of the magnet was about 46 to 223 mT between the sites of SBF measurement and the magnet. No intervention existed during other 30-minute intervals in either group. Thereafter, analysis of variance with repeated-measures combined with Bonferroni's multiple comparison tests was adopted to analyze the SBF value and its spectral variants obtained by wavelet transform. The major finding of this study was that SMF exposure induced significant increases in the absolute amplitudes of frequency band III and V (aIII and aV), which indicated intrinsic myogenic and endothelial related activities (P<0.05) respectively while the mean amplitude of SBF flux still maintain on the basal level (P>0.05). Furthermore, after removal of the SMF, variations of rhythmic flow motion of SBF in SMF exposure interval vanished gradually, which suggest the limitations of the deferred-effect of SMF on SBF.