Poincaré Plot in Capturing Nonlinear Temporal Dynamics of HRV

The method and importance of capturing temporal variation using standard descriptors (SD1 and SD2) of Poincare plot have been presented in Chap. 2. However, this does not include the temporal variation at point-to-point level of the plot. In addition, SD1 and SD2 descriptors are linear statistics (Brennan et al., IEEE Trans. Biomed. Eng. 48:1342–1347, 2001) and hence the measures do not directly quantify the nonlinear temporal variations in the time series contained in the Poincare plot. Although SD1/SD2 is considered as a nonlinear measure, it yields mixed results when applied to the data sets that form multiple clusters in a Poincare plot due to complex dynamic behaviours (Brennan et al., IEEE Trans. Biomed. Eng. 48:1342–1347, 2001). This is because the technique relies on the existence of a single cluster or a defined pattern (Christopher et al., Biophys. J. 82:206–214, 2002; Schechtman et al., Pediatr. Res. 40:571–577, 1996). Therefore, further studies are required in defining new descriptors for analysing temporal variability of time series using Poincare plots. Another driving force behind this study is the fact that the visual pattern of the Poincare plot of heart rate variability signals relies upon clinical scenarios and the application of the existing standard descriptors in various studies has resulted in limited success.