CONTINUOUS HEART-RATE-VARIABILITY MONITORING THROUGH COMPLEX DEMODULATION IMPLEMENTED WITH THE FAST FOURIER-TRANSFORM AND ITS INVERSE

A new method for the analysis of 24-hour heart rate variability (HRV) using complex demodulation (CDM) implemented with the fast Fourier tra nsform FFT) and its inverse is described. In a control group with-palp itations and dizzy spells (n = 30, 47.2 +/- 16.7 years) the relationsh ip between HRV parameters and subject age was investigated. CDM was us ed to obtain the amplitude and frequency of the low frequency (LF) and high frequency (HF) oscillations for 8 diurnal hours and 4 nocturnal hours. Differences between the two periods were seen in the LF/HF rati o (2.2 +/- 0.6 vs 1.5 +/- 0.6; P < 0.0001), HF amplitudes (12 +/- 6 vs 17 +/- 7 normalized units, P < 0.05), and in the mean frequency of th e LF oscillations (0.078 +/- 0.008 vs 0.073 +/- 0.007 Hz, P ( 0.01). D uring the daytime, age wets inversely correlated to HF amplitude (r = -0.60), directly correlated to HF mean central frequency (r = 0.40), i nversely correlated to LF amplitude (r = -0.55), and likewise inversel y correlated to LF mean central frequency (r = -0.74, P < 0.001). At n ight, age was only inversely correlated to HF amplitude and to LF mean central frequency. Conclusions: Continuous HRV monitoring through CDM implemented with the FFT and its inverse differentiates the periods o f diurnal activity and nocturnal rest as an expression of two differen t activity states of the autonomic nervous system. It allows nonstatio nary analysis, and separately provides mean and instantaneous oscillat ion amplitude and frequency. Subject-age is not equally related to mea n amplitude and frequency of a given oscillation.