title: Complexity of cardiovascular rhythms during head-up tilt test by entropy of patterns.
abstract: OBJECTIVE
  The head-up tilt (HUT) test, which provokes transient dynamical alterations in the regulation of cardiovascular system, provides insights into complex organization of this system. Based on signals with heart period intervals (RR-intervals) and/or systolic blood pressure (SBP), differences in the cardiovascular regulation between vasovagal patients (VVS) and the healthy people group (CG) are investigated.
  
  
  METHODS
  Short-term relations among signal data represented symbolically by three-beat patterns allow to qualify and quantify the complexity of the cardiovascular regulation by Shannon entropy. Four types of patterns: permutation, ordinal, deterministic and dynamical, are used, and different resolutions of signal values in the the symbolization are applied in order to verify how entropy of patterns depends on a way in which values of signals are preprocessed.
  
  
  RESULTS
  At rest, in the physiologically important signal resolution ranges, independently of the type of patterns used in estimates, the complexity of SBP signals in VVS is different from the complexity found in CG. Entropy of VVS is higher than CG what could be interpreted as substantial presence of noisy ingredients in SBP of VVS. After tilting this relation switches. Entropy of CG occurs significantly higher than VVS for SBP signals. In the case of RR-intervals and large resolutions, the complexity after the tilt becomes reduced when compared to the complexity of RR-intervals at rest for both groups. However, in the case of VVS patients this reduction is significantly stronger than in CG.
  
  
  CONCLUSIONS
  Our observations about opposite switches in entropy between CG and VVS might support a hypothesis that baroreflex in VVS affects stronger the heart rate because of the inefficient regulation (possibly impaired local vascular tone alternations) of the blood pressure.
authors.affiliation: University of Gdańsk, Institute of Experimental Physics, 80-308 Gdańsk, ul Wita Stwosza 57, Poland.
authors.forename: Dorota
authors.initials: D
authors.lastname: Wejer
authors.forename: Beata
authors.initials: B
authors.lastname: Graff
authors.forename: Danuta
authors.initials: D
authors.lastname: Makowiec
authors.forename: Szymon
authors.initials: S
authors.lastname: Budrejko
authors.forename: Zbigniew R
authors.initials: ZR
authors.lastname: Struzik
mesh_terms: D000328:Adult; D002320:Cardiovascular Physiological Phenomena; D019277:Entropy; D005260:Female; D006801:Humans; D008297:Male; D012815:Signal Processing, Computer-Assisted; D019462:Syncope, Vasovagal / Q000175:diagnosis / Q000503:physiopathology; D018667:Tilt-Table Test; D055815:Young Adult