Cardiac and Muscular Factors in the Microvibration on the Human Body Surface

Abstract

Mechanical oscillations on the body surface have been presumed to correspond with the rhythmical tendency of skeletal muscles and to be determined by the delay in the stretch reflex servoloop (LIPPOLD et al. '57). On the other hand, the oscillations in the spinal reflex arc have been emphasized to be directly responsible for the generation of the invisible microvibrations on the human body surface (SUGANO & INANAGA '60, '61). The present study began with the interest to the relation between the frequency characteristics of the global EMG and the mechanical vibrations on the body surface. The results are summarized as follows :1) The amplitude and the frequency of the microvibratinos were different among various sites of the body surface. It was indicated the amplitude of the vibrations was independent on the degree of the abundance of the muscular structure below the recording site. Besides differences between the absolute frequency of the vibrations and that of the EMG below the recording site, no parallelism between the frequency spectra of the vibrations and of the EMG was confirmed. In addition, the amplitude and the frequency spectra of the vibrations showed considerable variations within and among subjects, as compared with those on the global EMG.2) In the averaging addition performed synchronously with the R waves in the ECG of subjects, it was indicated that some components in the vibrations progressively developed as the addition time progressed. This syntonous component to the heart beats was present even when the muscles underlain below the recording surface contracted. The above results may be difficult to be explained without the role of the heart beats for the generation of the microvibrations.3) Cooling a foot with ice-water caused increases in the amplitude and highering in the spectra of the microvibrations with a transient decrease in the amplitude immediately after the commencement of the cooling. During the cold stimulation any remarkable changes in the heart rate were detected. This means that the increase in the amplitude and the highering in the spectra were caused from some factors having no direct connection with the cardiac cycles.4) When the muscles below the recording surface contracted, the amplitude of the microvibrations increased greatly, in particular, in the beta frequency ranges. However, the syntonous component to the cardiac beats was less in amount as compared with the calm state. This indicates that the increase in the amplitude and the highering in the spectra were also caused mainly from factors having nothing to do with the cardiac beats.5) The amplitude of the microvibrations became large and the frequency of those shifted to high when the contralateral muscles to the recording site contracted voluntarily. Also in this case, the syntonous component to the heart beats was indicated not to be responsible for the changes in the vibrations.6) It was supported that in the microvibrations there would be two factors, one is syntonous to the cardiac beats (the cardiac factor) and the other is drived from the muscle tonous (the muscular factor).