Diminished complexity of heart rate time series in adolescents facing negative events during everyday life

Physiological systems need to be flexible in order to adapt to a changing environment. Negative events, however, induce flexibility reductions that seem necessary for coping purposes. To date, studies have measured linear variability and entropy in heart output, but none have examined the scaling properties of the cardiac system when individuals deal with stressful everyday events. This study was aimed at testing the hypothesis that the complexity of the cardiac dynamics is diminished when individuals face negative events in real life. Cardiac variability (linear) and complexity (nonlinear), as well as discomfort and effectiveness of event-related emotion regulation (EER) were ecologically examined in N = 65 adolescents (Mage = 14.80 years; SDage = 0.86; 55.38% girls). Repeated Measures MANOVAs revealed higher heart rate (HR) and lower cardiac complexity (higher long-term scaling exponent, p = .029; lower Fractal Dimension FD, p = .030; and lower Sample Entropy, p = .001) during EER in comparison with non-emotion regulation conditions (NER). Wilcoxon non-parametric tests revealed higher Hurst exponents (p = .006) in EER than in NER. No significant correlations were found between discomfort and cardiac variables although the higher the cardiac entropy in NER conditions, the greater the self-rated effectiveness of EER (p < .050). EER processes involved increases in HR as well as scaling and FD changes that might reflect the real-time scale’s predominance in HR output when adolescents are dealing with negative events.