Heart Rate Variability in Stress-related Fatigue, Adolescent Anxiety and Depression and its Connection to Lifestyle

Abstract: Heart rate varies constantly as a consequence of activity in the sympathetic and parasympathetic autonomic nervous systems (SNS and PNS). In short-term recordings, heart rate variability (HRV) is mostly related to the inhibitory activity of the vagal nerves, which are part of the PNS. HRV is lower when under stress as well as in several illnesses and psychiatric conditions. Decreased HRV is also related to cardiac disease, which is the leading cause of death worldwide. Autonomic imbalance, measured as HRV, is suggested as a mediator between psychosocial distress and cardiovascular disease.The aim of the present thesis was to investigate the connection between HRV and psychosocial distress, including psychiatric problems (studies I and II), and lifestyle factors (study III). In study I, additional physiological measures sensitive to autonomic activity and results from a continuous attention test were investigated in parallel with HRV. In studies II and III the participants were adolescents.The results show that HRV is lower in women with stress-related fatigue and adolescent girls with a psychiatric diagnosis compared to healthy control groups. However, these groups did not exhibit an increase in physiological measures of SNS origin, which supports the assumption that the observed hyperarousal is related to decreased vagal activity rather than increased SNS activity. Women with stress-related fatigue made more impulsive errors and had a “risky” response style in the continuous attention test. There was a negative correlation between test performance and HRV. Decreased vagal activity is thus associated with deficient behavioural inhibition. In study III, HRV in a group of healthy adolescent boys and girls was positively associated with physical activity but not with other lifestyle measures.Even at young age HRV is a sensitive marker of autonomic imbalance resulting from psychosocial stress. Future longitudinal research will show whether HRV can be used for early identification of people at risk of cardiovascular disease and whether such interventions will lower the risk of cardiac morbidity.