| dc.description.abstract | Human body is an interesting complex network exhibiting multi-scales of nonlinearly coupled mechanical vibrations, even for a resting subject. For example, respiration, heartbeat, muscle tremor, and local artery pulsation are the possible sources inducing global or local mechanical vibrations.
In this work, skin vibrations of the different regions on the forearms of resting subjects, are explored, using a simple noncontact method, direct visualizing skin displacement through optical video microscopy by digital tracking skin tracer motions. The measurement provides a good bandwidth up to a few tens of Hz, and spatial resolution down to 1 um. The skin velocity field in the viewing plane can also be obtained from sequential images through particle image velocimetry (PIV). By comparing the vibrations of a pair of separated regions from two synchronized video-microscopes, the following interesting issues are addressed: (i) What are the generic behaviors and differences of skin vibrations of different regions, especially around radial artery, acupuncture points along the lung meridian and sham points? (ii) Are acupuncture points the singular points for skin vibrations? (iii) What are the origins for those skin vibrations, and how are different modes correlated?
It is found that, except the radial artery region, all other tested regions in forearms show similar vibration waveforms, originated from the global mechanical vibration induced by heartbeat and respiration in the trunk, regardless of whether there are nearby meridians. The global vibration contains a low-frequency respiratory mode around 0.2 Hz, and a middle-frequency band with distinguished fundamental heartbeat around 1 Hz and its few higher order harmonics, on a floor following power law decay. Moreover, a wide band bump centered around 10 Hz with a few Hz band width, out of the power law decay spectrum floor is observed. The band pass filtered 10 Hz high-frequency waveform is modulated by the heartbeat. The above observations suggest that heartbeat and respiration are the two major sources of trunk vibration and consequently global vibrations in upper limbs. Around the radial artery, superposed on the global vibration, arterial pulses induce additional local vibration. It only contains the middle-frequency modes from about 1 Hz to its harmonics up to a few Hz, excluding low frequency respiration and the 10 Hz high-frequency modes. The middle-frequency vibration induced by artery is phase-locked and frequency-locked with the middle-frequency global vibration, and is modulated by the slow respiration mode.
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