title: Excitation specificity of repolarization parameters.
abstract: The excitation specificity of QT dynamic parameters was tested on three groups of subjects: healthy subjects; non-medicated hypertensive subjects with metabolic syndrome; and subjects with essential hypertension. Four different excitations of RR were used: bicycling exercise; tilt with breathing 0.1 and 0.33 Hz; and deep breathing. Linear dynamic feedback model of QT/RR coupling was supposed at the analysis and next repolarization parameters were tested: QTc; gain of QT/RR coupling for slow and fast RR variability; time constant of QT adaptation; and random QT variability.
  
  
  RESULTS
  Dynamic repolarization parameters statistically significantly depend on the type of RR excitation. The gain of QT/RR coupling for slow RR variability, the time constant of QT adaptation and QTc are maximal at RR excitation given by the bicycling exercise. The frequency of breathing, i.e. corresponding vagal modulation has no effect on repolarization parameters. The measurements with deep breathing, without any other slow excitation of heart rate, has low signal-to-noise ratio of analyzed data and resulting QT parameters are inaccurate.
  
  
  CONCLUSIONS
  The use of heart rate excitation and all measurements conditions should be defined for the exact analysis of the repolarization dynamic parameters.
authors.affiliation: Institute of Scientific Instruments, Academy of Sciences, Czech Republic, Kralovopolska 147, 612 64 Brno, Czech Republic. josef@isibrno.cz
authors.forename: J
authors.initials: J
authors.lastname: Halámek
authors.forename: P
authors.initials: P
authors.lastname: Jurák
authors.forename: V
authors.initials: V
authors.lastname: Vondra
authors.forename: I
authors.initials: I
authors.lastname: Viščor
authors.forename: M
authors.initials: M
authors.lastname: Plachý
authors.forename: P
authors.initials: P
authors.lastname: Leinveber
mesh_terms: D000328:Adult; D000368:Aged; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016276:Ventricular Function / Q000502:physiology*; D055815:Young Adult