Assessment of vasomotor oscillations with Fourier analysis of biological tissue impedance

Abstract

Fourier analysis revealed a number of periodicities in small variations of bioimpedance of human finger including the major spectrum peaks at the frequencies of heart beats, respiration, and Mayer wave (0.1 Hz). These periodic variations of bioimpedance were detected under the normal conditions and during blood flow arrest in the hand by a pneumatic cuff placed on the arm. They are explained by periodic variations in systemic blood pressure and by oscillations of regional vascular tone resulted from neural vasomotor control. During normal blood flow, the greatest variations in bioimpedance were observed at the heart rate, and their amplitude surpassed by an order of magnitude the amplitudes of respiratory oscillations and Mayer wave. In contrast, during blood arrest, the largest amplitude of rhythmical changes of the impedance characterized the oscillations at respiration rate, while the amplitude of oscillations at the heart rate was the smallest. During normal respiration and circulation, two side cardiac peaks were revealed in bioimpedance amplitude spectrum which disappeared during respiration arrest and thought to reflect the amplitude respiratory modulation of the cardiac output via sympathetic influences. During normal breathing, the second and the third harmonics of the cardiac spectrum peak were split reflecting frequency respiratory modulation of the heart rate by parasympathetic influences. The results favour applicability of Fourier analysis of bioimpedance variations in assessment of regional neural influences and neurogenic modulation of cardiac activity.