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.

Multicycle harmonic (Fourier) analysis of bioimpedance was employed to simultaneously assess circulation and neural activity in visceral (rat urinary bladder) and somatic (human finger) organs. The informative value of the first cardiac harmonic of the bladder impedance as an index of bladder circulation is demonstrated. The individual reactions of normal and obstructive bladders in response to infusion cystometry were recorded. The potency of multicycle harmonic analysis of bioimpedance to assess sympathetic and parasympathetic neural control in urinary bladder is discussed. In the human finger, bioimpedance harmonic analysis revealed three periodic components at the rate of the heart beat, respiration and Mayer wave (0.1 Hz), which were observed under normal conditions and during blood flow arrest in the hand. The revealed spectrum peaks were explained by the changes in systemic blood pressure and in regional vascular tone resulting from neural vasomotor control. During normal respiration and circulation, two side cardiac peaks were revealed in a bioimpedance amplitude spectrum, whose amplitude reflected the depth of amplitude respiratory modulation of the cardiac output. During normal breathing, the peaks corresponding to the second and third cardiac harmonics were split, reflecting frequency respiratory modulation of the heart rate. Multicycle harmonic analysis of bioimpedance is a novel potent tool to examine the interaction between the respiratory and cardiovascular system and to simultaneously assess regional circulation and neural influences in visceral and somatic organs.

Статья поступила в редакцию 8 ноября 2018 г. Аннотация. Сигналы с квадратурной амплитудной манипуляцией давно и успешно применяются в цифровых системах передачи информации. Характеристики помехоустойчивости их приема на фоне белого гауссовского шума хорошо изучены. В статье методами статистической радиотехники проанализирована помехоустойчивость приема сигналов с квадратурной амплитудной манипуляцией в присутствии шумовой и гармонической помехи. Получены зависимости вероятности битовой ошибки от отношения сигнал/шум, от интенсивности помехи и от ее расстройки относительно центральной частоты спектра полезного сигнала. Показано, что прием сигналов с квадратурной амплитудной манипуляцией сильно ухудшается при наличии гармонической помехи и с увеличением позиционности сигналов это влияние усиливается. Наиболее опасной является прицельная гармоническая помеха, частота которой совпадает с центральной частотой спектра полезного сигнала. Ключевые слова: вероятность битовой ошибки, гармоническая помеха, квадратурная амплитудная манипуляция, помехоустойчивость.

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