title: Directionality in cardiovascular variability interactions during head-down tilt test.
abstract: A nonlinear model-free Granger causality approach was exploited to quantify the strength of the causal relation along cardiac baroreflex and cardiopulmonary pathway from spontaneous cardiovascular variabilities during head-down tilt (HDT). The analysis was completed through the assessment of traditional time and frequency domain parameters and cardiac baroreflex sensitivity. We found that, while respiratory sinus arrhythmia augmented, the power of the systolic arterial pressure variability in the low frequency band (i.e. from 0.04 to 0.15 Hz) decreased and cardiac baroreflex sensitivity increased, the strength of the causal relation along cardiac baroreflex and cardiopulmonary pathway remained constant. We conclude that, despite cardiopulmonary stimulation and sympathetic inhibition induced by HDT, neither cardiac baroreflex nor cardiopulmonary pathway took prevalence in governing heart period changes during HDT.
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Andrea
authors.initials: A
authors.lastname: Marchi
authors.forename: Vlasta
authors.initials: V
authors.lastname: Bari
authors.forename: Aparecida M
authors.initials: AM
authors.lastname: Catai
authors.forename: Stefano
authors.initials: S
authors.lastname: Guzzetti
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Raimondi
authors.forename: Riccardo
authors.initials: R
authors.lastname: Colombo
mesh_terms: D000328:Adult; D000368:Aged; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002319:Cardiovascular System / Q000503:physiopathology*; D004562:Electrocardiography; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D065809:Respiratory Sinus Arrhythmia / Q000502:physiology