title: The role of sympathetic and vagal cardiac control on complexity of heart rate dynamics.
abstract: Analysis of heart rate variability (HRV) by nonlinear approaches has been gaining interest due to their ability to extract additional information from heart rate (HR) dynamics that are not detectable by traditional approaches. Nevertheless, the physiological interpretation of nonlinear approaches remains unclear. Therefore, we propose long-term (60 min) protocols involving selective blockade of cardiac autonomic receptors to investigate the contribution of sympathetic and parasympathetic function upon nonlinear dynamics of HRV. Conscious male Wistar rats had their electrocardiogram (ECG) recorded under three distinct conditions: basal, selective (atenolol or atropine), or combined (atenolol plus atropine) pharmacological blockade of autonomic muscarinic or β1-adrenergic receptors. Time series of RR interval were assessed by multiscale entropy (MSE) and detrended fluctuation analysis (DFA). Entropy over short (1 to 5, MSE1-5) and long (6 to 30, MSE6-30) time scales was computed, as well as DFA scaling exponents at short (αshort, 5 ≤n≤ 15), mid (αmid, 30 ≤n≤ 200), and long (αlong, 200 ≤n≤ 1,700) window sizes. The results show that MSE1-5is reduced under atropine blockade and MSE6-30is reduced under atropine, atenolol, or combined blockade. In addition, while atropine expressed its maximal effect at scale six, the effect of atenolol on MSE increased with scale. For DFA, αshortdecreased during atenolol blockade, while the αmidincreased under atropine blockade. Double blockade decreased αshortand increased αlongResults with surrogate data show that the dynamics during combined blockade is not random. In summary, sympathetic and vagal control differently affect entropy (MSE) and fractal properties (DFA) of HRV. These findings are important to guide future studies.NEW & NOTEWORTHYAlthough multiscale entropy (MSE) and detrended fluctuation analysis (DFA) are recognizably useful prognostic/diagnostic methods, their physiological interpretation remains unclear. The present study clarifies the effect of the cardiac autonomic control on MSE and DFA, assessed during long periods (1 h). These findings are important to help the interpretation of future studies.
authors.affiliation: Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Luiz Eduardo Virgilio
authors.initials: LE
authors.lastname: Silva
authors.affiliation: Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Carlos Alberto Aguiar
authors.initials: CA
authors.lastname: Silva
authors.affiliation: Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Helio Cesar
authors.initials: HC
authors.lastname: Salgado
authors.affiliation: Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, São Paulo, Brazil rfazan@usp.br.
authors.forename: Rubens
authors.initials: R
authors.lastname: Fazan
mesh_terms: D000465:Algorithms; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D004347:Drug Interactions; D004562:Electrocardiography; D019277:Entropy; D006321:Heart / Q000187:drug effects / Q000294:innervation* / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010276:Parasympatholytics / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013565:Sympatholytics / Q000494:pharmacology; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*
chemical_list: D010276:Parasympatholytics; D013565:Sympatholytics; D001262:Atenolol; D001285:Atropine
keywords: autonomic nervous system; detrended fluctuation analysis; heart rate variability; multiscale entropy; nonlinear dynamics