CHARACTERIZATION OF ARM MICROVIBRATION RECORDED ON AN ACCELEROMETER

Microvibration (MV) of the freely hanging and firmly supported lower a rm was studied (n = 8) using two accelerometers, one located over musc le tissue (brachioradialis muscle) and one over bony tissue (processus styloideus). Measurements were made in the completely relaxed arm (RE ST), during arterial occlusion (CUFF) and during mild handgrip (GRIP), first with the arm relaxed and hanging beside the chair and then repe ated with the arm supported in a special rest. At REST, ballistocardia c forces were identified as the driving mechanism for the regular MV p attern, whereas actions of local pulse waves (CUFF) could be excluded. During GRIP irregular MV, related to the contraction process, became superimposed on both signals. The MV at REST was sensitive to arm posi tion. In the freely hanging state, when the arm was family coupled to the trunk, ballistocardiac body motion was present over bony tissue, p roducing a low damped 7-13 Hz resonant response over muscle tissue. In the supported state, the arm became isolated from body motions. Never theless, ballistocardiac forces reached the arm, producing smaller osc illatory responses over bone and muscle tissue. Regionally produced MV (GRIP) was not sensitive to arm position, but the spectrum content in the 7-13 Hz region was very similar to REST. From these results it wo uld appear, that a low damped 7-13 Hz resonance process exists in rela xed muscle tissue? which physiologically becomes stimulated by cardiac and muscle forces. From the close relationship of the simultaneous MV waveforms in the supported arm, evidence for mechanical coupling betw een bone and muscle tissue is given.