System identification of closed-loop cardiovascular control
mechanisms: pharmacologic autonomic blockade and postural
effects.
Mullen, Thomas J., Marvin L. Appel, Ramakrishna Mukkamala, Joanne M.
Mathiasm, Richard J. Cohen.
Harvard-MIT Division of Health Sciences and Technology,
Massachusetts Institute of Technology, Cambridge, MA
APStracts 3:0272H, 1996.
We applied system identification to the analysis of fluctuations in
heart rate, arterial blood pressure, and instantaneous lung volume in
order to characterize quantitatively the physiological mechanisms
responsible for the couplings between these variables. We
characterized two autonomically mediated coupling mechanisms (HR
BAROREFLEX representing the heart rate baroreflex and ILVHR
representing respiratory sinus arrhythmia), and two mechanically
mediated coupling mechanisms (CIRCULATORY MECHANICS representing the
blood pressure wavelet generated with each cardiac contraction and
ILVABP representing the direct mechanical effects of respiration on
blood pressure). We evaluated the method in humans studied in the
supine and standing postures under control conditions and under
conditions of -sympathetic and parasympathetic pharmacological
blockade. Combined -sympathetic and parasympathetic blockade
abolished the autonomically mediated couplings while preserving the
mechanically mediated couplings. 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 which provides means for creating a
closed-loop model of cardiovascular regulation for an individual
subject without altering physiological control mechanisms.
Received 28 August 1995; accepted in final form 21 June 1996.
APS Manuscript Number H815-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96