24 h sequential spectral analysis of arterial blood pressure and pulse interval in free-moving subjects.

A procedure for the 24 h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects has been developed. It includes: 1) sampling of a 24 h intra-arterial BP recording, extraction of the systolic (S) and diastolic (D) BP and PI from each heart beat followed by storage into separate series; 2) high-pass filtering and a splitting of each series into consecutive records of 256 values; 3) estimation of power spectral density (PSD) via FFT in each stationary record, and finally, computation of the power of each target oscillation. Using this procedure we analyzed data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique. The results revealed different patterns of the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. Moreover, in order to reinforce the meaning of the obtained results and to exclude the possible negative effects due to the drawbacks typical of the FFT algorithm, we also performed a second spectral estimate based on the AR modeling. The obtained results validates the FFT approach.