Time domain heart rate variability index for assessment of dynamic stress

Frequency domain heart rate variability (HRV) analysis has been extensively applied in assessment of mental/physical stress since it provides a non-invasive tool to assess the status of autonomic system (ANS). However, there are many situations, such as exercise, where the heart rare changes rapidly over time, making frequency domain analysis of HRV unsuitable because the assumption of stationarity is not satisfied. Meanwhile, the investigation of these rapid changes is of considerable interest. Here, the authors introduced a new simple time domain HRV index for the assessment if dynamic change of stress. The authors evaluated their index using the ECG data of healthy subjects who were doing physical/mental exercises. The results suggest that the authors' index is suitable for assessment of dynamic change of stress, and it is of higher selectivity in assessment of stress than classical time domain HRV indices.