Abstract
There is a small movement that is observed on the body surface (Microvibration: MV). It was first reported by H. Rohracher in 1946. Though it is still not cleared why and how the MV occurs, there are some papers about its clinical applications to the diagnosis of various autonomic nervous system condition. In this study, a MV measurement system has been developed. The MV signals are detected by using the acceleration sensors placed on the forehead and thenar. The MV power spectra are calculated by using an autoregressive model. The MV is quantified by the sum and appearance rate of MV spectra. The MV signals are stabilized after 5 minutes from the start of MV measurement. They are independent not only of wrist angle but also of opening and closing of both eyes.
Though there are variations between individuals and body areas in the MV sum, the appearance rate on the forehead MV belongs to S-type (the frequency band 5.5-7.5Hz is superior in the MV spectrum) in nearly 96% of subjects. On the thenar MV, it belongs to N-type (the band 7.5-13Hz is superior) in nearly 79% of subjects. The diurnal change of the forehead MV is almost proportional to the variation of heart rate. The autonomic nervous system affects the MV sum through cardiac function and respiration. The somatic nervous system affects the MV appearance rate through muscle activity. The central nervous system affects both the sum and appearance rate due to the emotions of the subject. Therefore the MV occurrence mechanism is based upon signals from the autonomic, somatic, and central nervous system.
