Fourier analysis of human finger bioimpedance variances.

Fourier analysis was employed to determine the amplitudes of spectrum components of small variations of electrical resistance (bioimpedance) in human finger recorded using an original hardware-software complex. It revealed periodic bioimpedance oscillations at the frequencies of heartbeats, respiration, and Mayer wave (0.1 Hz). These periodic variations were observed under normal conditions and during circulation arrest in the arm. It is concluded that the spectrum peaks of bioimpedance variations in the phalanx of human finger reflect periodic blood pressure changes in the major vessels and rhythmic neural control of the regional vascular tone. During normal blood flow, the greatest amplitude of rhythmic changes in bioimpedance was observed at the heart rate; it surpassed by an order of magnitude the amplitudes of respiratory oscillations and Mayer wave. In contrast, the largest amplitude of rhythmical changes of the impedance during circulation arrest corresponded to the oscillations at respiration rate, while the amplitude of variations at the heart rate was the smallest. Under circulation arrest, the maximum frequency of bioimpedance variations was approximately 1.4 Hz (the third respiratory harmonic), which indicates the upper limit of frequency range of neural modulation of vascular tone in human finger. During normal respiration and circulation, two side cardiac peaks were revealed in bioimpedance amplitude spectrum, whose amplitude reflected the depth of the respiratory amplitude modulation of pumping action of the heart. During normal breathing, the second and the third harmonics of the cardiac bioimpedance variations were split reflecting respiratory frequency modulation of the heart rate.