title: System identification of closed-loop cardiovascular control: effects of posture and autonomic blockade.
abstract: We applied system identification to the analysis of fluctuations in heart rate (HR), arterial blood pressure (ABP), and instantaneous lung volume (ILV) to characterize quantitatively the physiological mechanisms responsible for the couplings between these variables. We characterized two autonomically mediated coupling mechanisms [the heart rate baroreflex (HR baroreflex) and respiratory sinus arrhythmia (ILV-HR)] and two mechanically mediated coupling mechanisms [the blood pressure wavelet generated with each cardiac contraction (circulatory mechanics) and the direct mechanical effects of respiration on blood pressure (ILV-->ABP)]. We evaluated the method in humans studied in the supine and standing postures under control conditions and under conditions of beta-sympathetic and parasympathetic pharmacological blockades. Combined beta-sympathetic and parasympathetic blockade abolished the autonomically mediated couplings while preserving the mechanically mediated coupling. Selective autonomic blockade and postural changes also altered the couplings in a manner consistent with known physiological mechanisms. System identification is an "inverse-modeling" technique that provides a means for creating a closed-loop model of cardiovascular regulation for an individual subject without altering the underlying physiological control mechanisms.
authors.affiliation: Harvard-Massachusetts Institute of Technology, Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge 02139, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Mullen
authors.forename: M L
authors.initials: ML
authors.lastname: Appel
authors.forename: R
authors.initials: R
authors.lastname: Mukkamala
authors.forename: J M
authors.initials: JM
authors.lastname: Mathias
authors.forename: R J
authors.initials: RJ
authors.lastname: Cohen
mesh_terms: D000328:Adult; D001285:Atropine / Q000494:pharmacology; D001340:Autonomic Nerve Block; D001794:Blood Pressure; D002320:Cardiovascular Physiological Phenomena; D002319:Cardiovascular System / Q000187:drug effects*; D006339:Heart Rate; D006801:Humans; D008168:Lung / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009407:Nerve Block; D010275:Parasympathetic Nervous System / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology
chemical_list: D001285:Atropine; D011433:Propranolol