An algorithm for the analysis of the circadian profile of the arterial pressure in normotensive subjects

: In this paper we proposed the use of a spectral analysis technique, the fast Fourier transform (FFT), for the evaluation of the normal circadian blood pressure rhythm. By means of this algorithm it is possible to separate the slower and reproducible variations of the blood pressure profile (probably due to endogenous rhythm) from the faster and random ones (due to psychophysical status of the subject). The FFT technique is used for the analysis of ambulatory blood pressure monitorings obtained in 66 normotensive subjects (38 males and 28 females, mean age 35 +/- 10 years). Taking into account the mean duration of pressure variations related to major daily activities (e.g. sleeping, eating, etc) it is proposed to consider the first 10 harmonics as those having the main influence on the circadian blood pressure rhythm. The amplitude of the first 10 harmonics of the whole sample was evaluated by using the chi 2 and the Kolmogorov tests, and the results confirmed the assumption of a normal distribution of the amplitudes. The 95% confidence interval of these harmonics was chosen as the criteria for defining a normal range for the circadian blood pressure rhythm. This approach was tested in a group of 4 hypertensive patients showing that alteration of the circadian blood pressure rhythm can be easily diagnosed.