Heart rate variability as a clinical tool.

Power spectrum analysis of cardiovascular signal variability, and in particular of the RR period (heart rate variability), is a widely used procedure for the investigation of autonomic cardiovascular control and/or target function impairment. However, a correct methodology is essential to extract the information embedded in the frequency domain. This article has the main purpose of proposing a still wider clinical use of the spectral methodology. Indeed, with this procedure the state of the sympathovagal balance modulating the sinus node pacemaker activity can be quantified in a variety of physiological and pathophysiological conditions. Changes in the sympathovagal balance can be often detected in basal conditions; however, a reduced responsiveness to an excitatory stimulus is the most common feature that characterizes numerous pathophysiological states. Moreover, the attenuation of an oscillatory pattern or its impaired responsiveness to a given stimulus can also reflect an altered target function and thus can furnish interesting prognostic markers.