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Test of dynamic closed-loop baroreflex and autoregulatory control of total peripheral resistance in intact and conscious sheep

¹Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology and ²Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142

Submitted 30 May 2003 ; accepted in final form 23 June 2004

This is the first study able to examine and delineate the actual actions of the physiological mechanisms responsible for the dynamic couplings between cardiac output (CO), arterial pressure (P_a), right atrial pressure (P_RA), and total peripheral resistance (TPR) in an individual subject without altering the underlying regulatory mechanisms. Eight conscious male sheep were used, where both types of baroreceptors were independently exposed to simultaneous beat-to-beat pressure perturbations under intact closed-loop conditions while CO, P_a, P_RA, and TPR were measured. We applied the cardiovascular system identification method proposed in a companion paper (4) to quantitatively characterize the dynamic closed-loop transfer relations COP_a, P_RAP_a, P_aTPR, and P_RATPR from the measured signals. To validate the dynamic properties of the estimated transfer relations, the essential parts of the linear dynamics of the model were independently and comprehensively evaluated via error model cross-validation, and the overall model's steady-state behavior was compared with a separate random effects regression approach. In addition to numerous physiological findings, we found that the cardiovascular system identification results were exceptionally consistent with the analytically derived solutions previously discussed in Ref. 4. In conclusion, this study presents the first time validation of a cardiovascular system identification method by means of experimentally acquired animal data in the intact and conscious animal and offers a set of powerful quantitative tools essential to advancing our knowledge of cardiovascular regulatory physiology.

cardiovascular regulatory physiology; autonomic regulation; arterial and cardiopulmonary baroreceptors; local vascular autoregulation; system identification

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