Recurrence quantification analysis of heart rate during mental arithmetic stress in young females

The aim of this study is to investigate the effect of mental arithmetic challenge on recurrence plot-based complexity measures of heart rate in young healthy females. RR intervals were recorded in 50 healthy participants for 10 min in the rest and mental arithmetic stress states. The complexity of the heart rate was assessed through recurrence quantification analysis (RQA). The RP showed a consistent pattern of more clustering of points during mental stress, with respect to the rest. This suggests that recurrence of heart rate underwent a notable evolution during the transition from rest to mental stress. Thus, the RPs can sensitively reflect the signals from different physiological states. The recurrence plots during mental stress are characterized by the larger length of vertical lines (TT) and a higher percentage of points forming diagonal lines (DET). The results of the research indicate that deterministic structure was present in the heart rate dynamics (DET was statistically greater than 0), but that heart rate variations were not completely deterministic (DET was statistically less than 1). The statistical analysis of RQA measures reveals significant changes in DET, LAM, LMAX, Vmax, and TT during mental stress. Mental arithmetic induced a significant increase of DET to rather a high level. High level of DET indicates that recurrence points are mainly forming diagonals and associated with high predictability of heart rate regulation system. Mental stress elicits a significant increase in the maximum length of the diagonal line LMAX (and decrease in LLE) that indicate diminishing the sensitivity of the heart rate regulation system to initial conditions. We compared rest and stress levels of LAM and TT, and we found the long permanence of the system in a particular state during mental stress.

Conclusion. We found that RQA measures of heart rate signals are sensitive to changes in autonomic tone induced by mental arithmetic stress. The recurrence analysis revealed a decrease in the complexity of heart rate variability during mental stress