RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt
Articolo
Data di Pubblicazione:
2010
Citazione:
RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt / A. Porta, E. Tobaldini, T. Gnecchi Ruscone, N. Montano. - In: AMERICAN JOURNAL OF PHYSIOLOGY. HEART AND CIRCULATORY PHYSIOLOGY. - ISSN 0363-6135. - 298:5(2010), pp. H1406-H1414. [10.1152/ajpheart.01206.2009]
Abstract:
Open-loop linear parametric models were exploited to describe ventricular repolarization duration (VRD) variability during graded head-up tilt. Surface ECG and thoracic movements were recorded in 15 healthy humans (age: 24-54 yr, median: 28 yr; 6 women and 9 men). Tilt table inclinations ranged from 15 to 90° and were varied in steps of 15°. All subjects underwent recordings at every step in random order. Heart period was assessed as the time difference between two consecutive R-wave peaks (RR) and the respiratory signal (R) as the sampling of the thoracic movement signal at the R-wave peaks. VRD was measured automatically as the temporal difference between the R-wave peak and T-wave apex (RTa) or T-wave end (RTe). The best model decomposed RT variability as due to RR changes (RR-related RT variability) to direct respiratory-related inputs (R-related RT variability) and to unknown rhythmical sources unrelated to RR changes and R (RR-R-unrelated RT variability). Using this model, RTe variability was found to be less predictable than RTa variability and composed of a smaller fraction of RR-related RT variability and a larger fraction of RR-R-unrelated RT variability. Predictability progressively decreased with tilt table angles, suggesting increased complexity of RT regulation. RT variance progressively increased with tilt table inclination. This increase was characterized by a gradual rise of the amount of RR-R-unrelated RT variability, whereas the amount of RR-related RT variability remained unchanged. These results suggest that the amount of RT variability, complexity of RT dynamics, and amount of RR-R-unrelated RT variability increase with the magnitude of the sympathetic drive directly related to tilt table inclination. We propose the utilization of the amount of RR-R-unrelated RT variability instead of overall RT variability as an indirect measure of autonomic regulation directed to ventricles.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Autonomic nervous system; Modelling; QT measurement; QT variability; QT-RR relationship
Elenco autori:
A. Porta, E. Tobaldini, T. Gnecchi Ruscone, N. Montano
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