Background. Blood pressure fluctuations over the 24 hours include both fast and slow changes. While most studies have focused on the former components, recent evidence suggests that also slower blood pressure variations may have physiological and clinical relevance. A method recently proposed to quantify these slower blood pressure components is broad band spectral analysis.

Methods and Results: Broad band spectral analysis consists in the estimation of a single spectrum obtained by considering all data included in a long term recording and in the quantification of the power of all frequency components, from the slowest to the fastest ones. Application of this method to recordings obtained in animais before and after surgical baroreceptor denervation has shown that not only fast but also slow blood pressure and heart rate fluctuations are under baroreflex control. Clinical applications of broad band spectral analysis have included 1] the quantification of the age-induced changes in the different components of blood pressure and heart variability, 2] the assessment of the effects of treatment on blood pressure and heart rate fluctuations in hypertensive patients, and 3] the assessment of the prognostic value of slow heart rate fluctuations in post-myocardial infarction patients.

Conclusions: Broad band spectral analysis represents a unique tool for the quantification of all components of blood pressure and heart rate variability and for the assessment of their possible changes in diseased conditions or under the effects of treatment.