Increasing sensitivity in the measurement of heart rate variability: The method of non-stationary RR time-frequency analysis

► Our aim was to develop algorithms of HRV time-frequency analysis. ► We introduce a novel notion of the fragmentary spectrum. ► The fragmentary spectrum is calculated by the similar basis function algorithm. ► The algorithm is applicable to signal segments of arbitrary length. ► We have developed a measure that we call the “RR deltagram”.