A new approach for evaluating circadian blood pressure levels and variability from 24 h ambulatory blood pressure profiles.

In 24 h blood pressure monitoring the severity of arterial hypertension is generally classified on the basis of the arithmetic mean of the diastolic blood pressure between 6 AM and 10 PM. In the present study Fourier analysis was used for evaluation of circadian blood pressure level and variability. A common reference profile was calculated on the basis of a group of 50 normotensive profiles. This reference profile is characterized by the fact that the sum of the squares of the distances between the individual profiles and the reference profile is a minimum. The individual 24 h profiles of 103 patients with untreated arterial hypertension were also each described by a Fourier series and were then compared with the normotensive reference profile. The comparison was made not only with respect to the absolute pressure over 24 h but also with respect to the circadian fluctuations in blood pressure. Our results show that the Fourier analysis of 24 h blood pressure profiles presented here can be used for more precise evaluation of 24 h blood pressure profiles.