Effect of Random Frequency Modulation on ECG Power Spectra

Electrocardiographic signals are an example of biological signals whose fundamental characteristics may be altered by environmental factors. Frequency modulation due to the influence of respiration and other factors may alter the signals and affect the characteristic power spectrum. Here the effects of random frequency modulation on ECG power spectra are examined in two cases: when there is random phase modulation in the periodic Fourier series model and when the consecutive cycles for a given sequence of beats deviate from periodicity due to random variation in the fundamental frequency about its mean. It is concluded that the differential effects of random frequency modulation on the power spectrum can be detected and its contribution defined. Thus, the underlying power spectrum of identical signals with and without random phase and frequency modulations can be defined.