The impact of cardiac activity on triaxially recorded endogenous microvibrations of the body

The influence of cardiac activity on the endogenous microvibrations of the body (MV) was studied in a total of 37 young, healthy subjects. The force oscillations and the rectified and integrated force-time function in the three space directions were simultaneously recorded with the ECG and the arterial pulse during quiet bipedal standing before (control) and after isoprenaline inhalation, a work load of 150 W, and mild cold stress. In the vertical force component (Fz) 27 out of the 37 subjects showed cardiac characteristics similar to the ballistocardiogram. After isoprenaline or exercise, all 37 subjects showed these cardiac characteristics in Fz, and the maximal amplitudes as well as the rectified impulse values were increased in the three directions, but particularly in the z-axis. The propagation of the MV through the body was independent of the arterial pulsation. The increase in muscle tone due to cold stress led to a significant increase of the rectified impulse only in the sideward direction (SY). It is concluded that the triaxially recorded MV arise from cardiac activity, mainly reflected in the vertical (z) axis, and from skeletal musculature representing a mechanical oscillating system with varying material constants (muscle tension, inertial forces, etc.).