Frequency Domain Analysis

The sympathetic and parasympathetic branches of the ANS strongly influence heart rate. Afferent sympathetic activity increases heart rate, while afferent parasympathetic activity decreases heart rate. The speed with which changes in these systems are reflected in changes in heart rate is different. The sympathetic system is slow in its effects (a few seconds), while the parasympathetic system is faster (0.2–0.6 s). Given the different speeds of response, it is possible to use frequency analysis to study sympathetic and parasympathetic contributions to the HRV. A key fact to keep in mind in this analysis is that the RR series is not stationary. In this chapter, we will see how to perform HRV frequency analysis using RHRV.