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

本研究旨在探究心算任务对年轻健康女性心率的基于递归图的复杂度指标的影响。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。通过递归定量分析（Recurrence Quantification Analysis, RQA）评估心率复杂度。结果显示，相较于静息状态，心算应激状态下的递归图（Recurrence Plot, RP）呈现出点簇集更为显著的一致模式。这表明，心率的递归特性在从静息向心理应激的转变过程中发生了显著演化，因此递归图能够灵敏地反映不同生理状态下的信号特征。心算应激状态下的递归图以更长的垂直线段长度（TT）以及更高的形成对角线的点占比（DET）为特征。本研究结果表明，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指标的统计学分析显示，心算应激期间，DET、LAM、LMAX、Vmax及TT均发生显著变化。心算任务使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，且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下降。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持续时间更长。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。