A Systematic Review of the Relationship between Psychological Stress Protocols and Non-linear Heart Rate Variability

The use of stress training induction is very important for psychology and neuroscience studies. It allows the researcher to manipulate the emotional activation of subjects to determine its effect on their behavior. This study was performed to explore the link between stress and heart rate variability (HRV) measures. HRV in the field of the nonlinear domain is also useful in determining the autonomic balance and is a more reliable marker of mortality and problems in patients with cardiovascular diseases. These protocols let researchers examine the physiological paths of a stress reaction in physical condition and infection, which is crucial to stress research. This study aimed to support reliable information about psychological stress protocols and HRV measures during nonlinear measures. To conduct a systematic review of the evidence, a meta-analysis of the proof was carried out according to the inclusion criteria, performing a comprehensive search of electronic sources and a linear review of references. Once conference papers were removed, journal papers illustrating well-made studies analyzing HRV with healthy subjects were considered for inclusion if the stress-inducing protocols were the same. A total of 147 volunteers were enrolled in the four studies, which investigated 11 non-linear HRV measures. Mental Arithmetic Task is primarily used as a stress-inducing test, and three studies extracted SD1, SD2, and SD1/SD2 for HRV non-linear measurements. This study shows that induction of mental stress can increase the levels of cortisol in healthy subjects. In conclusion, the results showed that investigating nonlinear HRV measures for the duration of mental stress is still needed. Furthermore, the nonlinear HRV measures can be spread over to other fields where HRV has been shown to be clinically meaningful.