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