Research On Physiological Patterns Of Heartbeat Under Stress

Stress is a state in which an individual increases the physical,mental,emotional,and behavioral demands that make the body unbalanced.Stress can cause a strong physiological arousal,usually combined with significant physiological response of sympathetic nerve system and deactivation of the parasympathetic nerve system.In addition,stress has a strong association with cardiac activity.Numerous studies show that long-standing psychological stress may cause a variety of physical damage,e.g.increased risk of cardiovascular disease caused by adverse autonomic nerve conduction of the heart.Therefore,the study of the physiological response pattern under stress is a meaningful research work.In this paper,we investigated the stress patterns of heartbeat during the stress caused by mental stimulus,physical stimulus and mixed stimulus respectively.(1)We design three kinds of experiments to acquire the electrocardiograms under different stress.Firstly,the physiological response samples under mental stress are obtained by the reading task without specific requirements,the simulated thesis defense and the real-scene thesis defense for master's degree.Secondly,the physiological response samples under physical stress are obtained by the sitting still task,the slow running task and rapid up and down stairs task.Finally,the physiological response samples to mixed stress stimulus are obtained by the sitting still task,the ultrasonic scaling with background music event and the ultrasonic scaling without background music event.Using the subjects' self-reported stress experience,we determine the stress level of each physiological data record.Then,we construct ECG data sets corresponding to the weak,medium and strong stress.(2)The trend of the average effect of physiological parameters under different stress conditions are discussed from a statistical view.Using t-test statistical analysis,it is found that the changes of physiological parameters are different under different stress levels,which reveal stress-related cardiac autonomic nervous activity.With the increase of stress level,the mean of the RR intervals shows a decreasing trend,reflecting accelerated heart rate and higher physiological arousal.The standard deviations of the RR intervals,the standard deviations of the first difference of the RR intervals and the mean square of the first differences of the RR intervals show a decrease trend with increasing stress level,indicating stress-aroused sympathetic activation and parasympathetic deactivation.At the same time,the non-linear characteristic of approximate entropy,determinism and Shannon entropy show an increasing trend,showing stronger uncertainty and complexity of the cardiac activity and larger adaptability of heartbeat under higher stress level.Finally,compared with that in physical stress state,the average change of physiological parameters show more complicated and uncertain cardiac activity in mental stress state.(3)The distinguishability of physiological patterns under different stress levels caused by different stimuli are discussed by using pattern recognition methods.The backward feature selection with certain classifiers obtain the most effective and brief expression of the stress heartbeat patterns.It is found that,without considering the stress stimuli,the physiological patterns of different stress levels are easy to be distinguished from each other.But if the stimuli of stress are taken into account,stress levels caused by different stimuli are hard to be distinguished.In this paper,statistical analysis and pattern recognition are applied to explore the physiological patterns of heartbeat under stress.The results show that the physiological parameters could reflect the autonomic nervous reactivity of stress.The excellent distinguishability of three stress levels by using the physiological parameters has an important practical significance for real-time stress monitoring with the aid of wearable equipment in the future.