[A study on the mechanism of microvibration changes in patients with eating disorders]

Microvibration (MV), which is a minute vibration observed on the human body surface, has been used clinically as a simple test for the autonomic nervous system function in psychosomatic medicine. The analogue frequency analysis has shown four different MV types in healthy subjects, depending on a major frequency component of MV. Although N type, a MV type with predominant frequencies being in the alpha band, is most common in healthy subjects, we have found that F type, the predominant frequencies being in the fast frequency (beta) band, is most common in patients with psychosomatic disorders, particularly in those with eating disorders. We have developed a system of digital frequency analyses of MV on a personal computer, in which the Fast Fourier Transform (FFT) and the reverse FFT are employed. In this study, the physiological significance of MV changes was investigated in patients with eating disorders, utilizing frequency analysis methods of the analogue and digital systems. The following results and conclusions were obtained. (1) A multiple regression analysis was performed to clarify the relationship between somatic severity (body weight change) and MV frequency bands by the analogue method in 57 patients with eating disorders. Percent change of body weight (% BW) was used as a target (dependent) variable, and 6 frequency bands of MV energy % were used as explanatory (independent) variables. The alpha 1 (7.5-8.5 Hz) and the beta (13-20 Hz) bands were selected as having a high explanatory power for % BW, with the alpha 1 band being greater than the beta band. This indicated that the reduction of % BW had a higher correlation with the decrease of the alpha 1 band than with the increase of the beta band. (2) The reverse FFT of a MV power spectrum was calculated with the digital method to extract frequency bands that was time-locked with ECG. This revealed that the time-locked oscillations were always found in the alpha band in either normal subjects or patients with eating disorders, regardless of the MV type. This indicated that the ballistocardiographic component of MV is included in the alpha band. (3) Putting all these results together, it is concluded that, in patients with eating disorders, the predominance of the beta band in MV (the F type) is caused by the decrease of the ballistocardiographic component of MV.