The effect of mental arithmetic stress on the nonlinear dynamics of heart rate in young females: recurrence quantification analysis.

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<b></b><i></i><br>

本研究旨在探讨心算任务对健康年轻女性心率的递归图复杂度指标的影响。研究招募50名健康受试者，分别在静息状态与心算应激状态下记录10分钟的RR间期数据。采用递归定量分析（recurrence quantification analysis, RQA）对心率复杂度进行评估。相较于静息状态，心算应激期间的递归图（recurrence plot, RP）呈现出一致的点聚集模式，这表明心率的递归特性在从静息状态向心理应激状态转变的过程中发生了显著变化。因此，递归图能够灵敏地反映不同生理状态下的信号特征。心算应激期间的递归图以更长的垂直线长度（TT）与更高的对角线点占比（DET）为特征。研究结果显示，心率动力学中存在确定性结构（DET在统计学上显著大于0），但心率变异并非完全确定性（DET在统计学上显著小于1）。对RQA指标的统计学分析表明，心算应激期间，DET、LAM、LMAX、Vmax及TT均发生了显著变化。心算任务可使DET显著升高至较高水平，高DET值意味着递归点主要以对角线形式聚集，这与心率调节系统的高可预测性相关。心理应激会使对角线最大长度LMAX显著升高（同时LLE降低），这表明心率调节系统对初始条件的敏感性有所降低。本研究对比了静息与应激状态下的LAM与TT水平，发现心理应激期间系统在特定状态下的停留时间更长。结论：本研究发现，心率信号的RQA指标对心算应激诱导的自主神经张力变化具有敏感性。递归分析揭示，心理应激期间心率变异性的复杂度有所降低。