Assessment of heart rate irreversibility induced by graded sympathetic activation in humans

• Published in: The FASEB journal 2007-04, Vol.21 (5), p.A564-A564
• Main Authors: Casali, Karina Rabello, Casali, Adenauer Girardi, Tobaldini, Eleonora, Gnecchi‐Ruscone, Tomaso, Montano, Nicola, Porta, Alberto
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.21.5.A564-c

Heart rate (HR) changes are mainly mediated through the modulation of sympathetic and vagal neural activities. Physiological behavior of these neural outflows is characterized by reciprocal relationship around an equilibrium state. Statistical irreversibility (SI) is a fundamental characteristic to evaluate disequilibrium in a dynamical system. Recently, SI studies applied to HR in physiological and pathological conditions characterized by sympathetic predominance, such as aging and heart failure (Costa et al, PhysRevLett 2005), reported significant changes in SI. To test whether these reversibility alterations are related to sympathetic activation (SA), we applied standard SI detections techniques (surrogate data approach based on the skewness of the prime variations series) to short‐term HR time series during a progressive SA induced by graded tilt. ECG signals were continuously recorded from ten healthy subjects, submitted to tilt at 0, 15, 30, 45, 60, 75 and 90 degrees and HR time series were obtained. We found SI in 50%, 60%, 80%, 30%, 90%, 70% and 80% of the subjects in respect to increasing tilt degrees. While supporting a coarse relationship between SA and SI in HR, the well known progressive SA was not associated with parallel increase in SI, indicating that SI in HR variability series extracted from physiological conditions is weakly related to the progressive changes in SA. Support: CAPES/Brazil; FIRST 2005 grant University of Milan.