njit-etd2003-081 - New Jersey Institute of Technology

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viewing the time series of sequential heart periods and blood pressure in the frequency
domain, spectral analysis decomposes the summed sinusoids into constituent frequencies.
The frequencies of interest in the study of RSA are the frequencies associated with
the normal spontaneous respiratory activity. If the breathing were constant at a rate of 16
times a min, each breath would take appropriately 3.745 sec and would have a frequency
of 0.267 cycles/sec (0.267 Hz). In Figures 5.1 (c) and 5.2 (c), the power density spectra
for each frequency of heart rate and blood pressure are plotted. These analyses were
conducted on the data plotted in Figures 5.1 and 5.2 (b). Note that both series exhibit a
peak power density estimate at the same frequency, representing the dominant or most
characteristic respiratory frequency of 0.267 Hz.
Even though the spectral decomposition of both heart rate and blood pressure
processes results in similar dominant frequencies, each process exhibits other prominent
frequencies, independent of respiration, that have been theoretically associated with other
physiological processes such as temperature and hormonal fluctuations [19].