Variability and similarity of inter-beat intervals of the heart as markers of perceived stress and behavioral regulation

Abstract

The current dissertation investigated inter-beat interval (IBI) indices of variability and similarity, reflecting autonomic nervous system (ANS) modulation on heart rate. IBI indices of cardiac vagal activity (CVA) are further considered to reflect activity in brain areas involved in self regulation. Yet, it is unclear which specific aspect(s) of self-regulation such IBI indices load most highly on, and their relation to contextual factors. Thus, in a sample of college students (n = 143) in paper I, we investigated how CVA and perceived stress associated with contextual factors of perceived social support and sex. Moreover, we expected indices to load highly on the internal regulation of perceived stress, compared to the external regulation of behavior. This was examined in adolescents with attention-deficit/hyperactivity disorder (ADHD) and controls (n = 67) in paper II. In paper III, we investigated the use of a nonlinear, graph theory-based method for illustrating IBI differences in adolescents with ADHD and controls (n = 73). In all studies, IBI indices were derived from short-term resting electrocardiogram (ECG) recordings, with high frequency-heart rate variability (HF-HRV) as the applied measure of CVA. Self-report questionnaires assessed emotion regulation difficulties (the Difficulties in Emotion Regulation Scale) perceived stress (the Perceived Stress Scale), and perceived social support (The Medical Outcomes Study Social Support Survey). In the moderation analysis of paper I, CVA associated positively with perceived social support in females with intermediate and high, compared to low, perceived stress levels, but not in males. Linear regression analyses in paper II showed that CVA associated negatively with access to emotion regulation strategies in adolescents with ADHD and controls. In paper III, independent samples t-test showed that the similarity graph algorithm illustrated IBI differences between the ADHD and control groups which traditional CVA analyses did not. In sum, the studies suggest that CVA might mark perceived stress regulation, and emphasize the consideration of contextual factors such as perceived social support and sex in the interpretation of this marker. Furthermore, the similarity graph algorithm might increase the sensitivity of IBI markers, possibly also indexing behavioral regulation. Although further research is required, IBI markers might have potential clinical use in the diagnosis, monitoring and treatment of psychiatric disorders.