title: Accounting for respiration is necessary to reliably infer Granger causality from cardiovascular variability series.
abstract: This study was designed to demonstrate the need of accounting for respiration (R) when causality between heart period (HP) and systolic arterial pressure (SAP) is under scrutiny. Simulations generated according to a bivariate autoregressive closed-loop model were utilized to assess how causality changes as a function of the model parameters. An exogenous (X) signal was added to the bivariate autoregressive closed-loop model to evaluate the bias on causality induced when the X source was disregarded. Causality was assessed in the time domain according to a predictability improvement approach (i.e., Granger causality). HP and SAP variability series were recorded with R in 19 healthy subjects during spontaneous and controlled breathing at 10, 15, and 20 breaths/min. Simulations proved the importance of accounting for X signals. During spontaneous breathing, assessing causality without taking into consideration R leads to a significantly larger percentage of closed-loop interactions and a smaller fraction of unidirectional causality from HP to SAP. This finding was confirmed during paced breathing and it was independent of the breathing rate. These results suggest that the role of baroreflex cannot be correctly assessed without accounting for R.
authors.affiliation: Department of Technologies for Health, Galeazzi Orthopedic Institute, University of Milan, 20161 Milano, Italy. alberto.porta@unimi.it
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Tito
authors.initials: T
authors.lastname: Bassani
authors.forename: Vlasta
authors.initials: V
authors.lastname: Bari
authors.forename: Gian D
authors.initials: GD
authors.lastname: Pinna
authors.forename: Roberto
authors.initials: R
authors.lastname: Maestri
authors.forename: Stefano
authors.initials: S
authors.lastname: Guzzetti
mesh_terms: D000328:Adult; D000465:Algorithms; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002320:Cardiovascular Physiological Phenomena; D003198:Computer Simulation; D004562:Electrocardiography; D005246:Feedback; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008955:Models, Cardiovascular; D012143:Respiratory Physiological Phenomena; D012146:Rest / Q000502:physiology; D016683:Supine Position / Q000502:physiology