Acute Mental Stress Detection via Ultra-short term HRV Analysis

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Acute Mental Stress Detection via Ultra-short term HRV Analysis R. Castaldo1, P. Melillo2, L. Pecchia1 1

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School of Engineering, University of Warwick, Coventry, United Kingdom Multidisciplinary Department of Medical, Surgical and Dental Sciences, Second University of Naples, Italy

Abstract: Acute mental stress reduces working performances and is one of the first causes of cognitive dysfunctions, cardiovascular disorders and depression. Stress detection via short term (5 minutes) Heart Rate Variability (HRV) has been widely investigated in the last years. Recent improvements in wearable sensing devices and mobile computing raised a new research question: is ultra-short (2 minutes) HRV as effective as the short term one to detect mental stress? This study aimed to answer this research question. Short and ultra-short HRV was compared in 42 healthy subjects (age 25-38 years) undertaking the widely adopted and highly-effective the Stroop Color Word Test (CWT). ECG signals were recorded during rest and stress session using a chest wearable monitoring device, the BioHarness M3 (ZephyrTech, NZ). HRV measures were then extracted and analyzed according to the literature and using validated software tools. Variations between short and ultra-short HRV measures in rest and stress sessions were analysed with the statistical Wilcoxon significance test. The results of the current study suggested that 6 HRV measures are effective in detecting acute mental stress both using short and ultra-short term analysis: Mean RR, Low Frequency power, Sample Entropy, Detrended fluctuation analysis: Short term and Long term fluctuation slope and Mean line length of Recurrence plot analysis .

Previous studies have focused the attention on the detection of acute mental stress by the assessment of the HRV in long and short term but only few studies [8-11] have investigated the effect of acute mental stress through ultra-short term HRV analysis. Recent improvements in wearable sensing devices and mobile computing raised a new research question: is ultrashort HRV analysis as effective as the short term one to detect mental stress? This study aimed to answer this research question. Several methods have been proposed to induce acute mental stress, including arithmetical tasks, computer games, academic examinations and so forth[12]. In the current study, mental stress was inducted using the Stroop Color Word Test (CWT), which was proved to be an effective and easily standardized method to induce mental stress. The goal of this study was to explore which ultra-short term HRV measures are as reliable as short-term ones to detect mental stress.

Keywords— Acute Mental Stress, HRV (Heart Rate Variability), Stroop Color Word Test (CWT).

A. Subjects

I. INTRODUCTION

Acute mental stress may cause cognitive dysfunctions, cardiovascular diseases, hypertension and depression[1, 2], reduce performances on the work place or in daily life[3] and increase the direct and indirect costs associated with health mental problems [4]. Mental stress influences the functionality of the Autonomous Nervous System (ANS), which controls the functionality of the heart, blood vessels and other organs [3, 5]. Therefore, acute stress may be assessed monitoring those physiological signals and parameters reflecting ANS statuses [6]. Numerous studies assessed the acute mental stress analyzing the Heart Rate Variability (HRV), whose measurements provides an indirectly measure of sympathetic and parasympathetic modulation [6]. HRV can be analyzed in time, frequency and in the so called non-linear domain performing long (24h), short (5 minutes) and ultra-short term (