Background and aims: Orthostatic hypotension (OH) is a common manifestation of abnormal blood pressure (BP) regulation. The relative contribution and interaction of the physiological systems that alter or maintain adequate BP is largely unknown. Developing a closed-loop model is
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Background and aims: Orthostatic hypotension (OH) is a common manifestation of abnormal blood pressure (BP) regulation. The relative contribution and interaction of the physiological systems that alter or maintain adequate BP is largely unknown. Developing a closed-loop model is necessary to investigate the complex physiological function and interaction and can give a better insight in the factors contributing to OH. The aim of this study is to describe and validate a closed-loop model of the BP regulation system that describes a posture related BP drop and subsequent recovery. Methods: The procedure to validate the face-validity of the closed-loop model consists of: 1) simulating the closed-loop model and 2) subsystems separately, to compare them to equivalent experimental data; 3) evaluate model simulations based on physiological knowledge (predetermined hypotheses); and 4) evaluating which parameters dominate the closed-loop model behavior of the BP signal by performing a sensitivity analysis. Furthermore, model adjustments have been made as a first attempt to improve face-validity, i.e. control adjustments of the time-varying controlled parameters representing the autonomic regulation.
Key results: For subsystem ‘cardiovascular system’ the cross-correlation coefficient and VAF for the signals indicate that the model is able to predict the behavior of the equivalent experimental data. Furthermore, adaptation of the heart rate (HR) to the change of the tilt can be seen. The BP decreases, which is detected by the autonomic nervous system which in turn increases the HR. However, the model does not compensate for the posture related BP drop. Not when systematically changing parameter values, changing parameters to optimal values simultaneously or amplifying the signals of the time-varying controlled parameters representing autonomic regulation. Conclusions: The closed-loop model shows reasonable face-validity with respect to the posture related BP drop in healthy young adults, but poor face-validity with respect to the BP recovery. Indicating that the subsystems modeling the mechanical properties of the cardiovascular system and hydrostatic pressure differences adequately represent physiology, in contrast to the subsystems aiming to actively restore BP. Future research should improve model elements representing the autonomic regulation, i.e. the control of time-varying parameters due to autonomic regulation on posture related BP changes.