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 is discussed. It includes: (1) sampling of a 24-h intra-arterial BP recording and extraction of the systolic and diastolic 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; and (3) estimation of power spectral density via fast Fourier transform (FFT) in each stationary record and computation of the power of each target oscillation. Using this procedure data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique was analyzed. The results revealed different patterns for 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. A second spectral estimate based on autoregressive modeling was performed. The results validate the FFT approach.