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UBC Theses and Dissertations

Homeostasis revisited in the genesis of stress reactivity Ataee, Pedram


Autonomic-cardiac regulation operates through interactions between the autonomic nervous system (ANS) and the cardiovascular system (CVS). In order to maintain homeostasis in the CVS, the ANS adjusts it effectors, such as the stiffness of blood vessels and the pace of heartbeats, against physical and psychological stressors, so that it can maintain adequate blood flow. This allows oxygen and nutrients to be delivered to organs and enables the performance of other essential functions. Autonomic-cardiac regulation can be described by a mathematical model and it can be analyzed under different scenarios such as a stressful condition or an increased arterial stiffness. This may help researchers to obtain new understandings of the autonomic-cardiac regulation. This thesis is built upon a physiology-based mathematical model of autonomic-cardiac regulation describing the regulation of heart rate (HR) and blood pressure (BP), using a set of nonlinear, coupled differential equations with delay. Non-invasive and subject-specific monitoring of autonomic-cardiac regulation has the potential to improve current treatments of autonomic-cardiac disorders. A parameter estimation method has been used to specify time-varying subject-specific model parameters associated with autonomic-cardiac regulation. The proposed method will help to improve monitoring of autonomic-cardiac variables, such as sympathetic and parasympathetic nerve activities affecting the heart and sympathetic nerve activity affecting the arterial tree. The complex dynamic interactions between nonlinearities and delays in the autonomic-cardiac regulation may result in the onset of instabilities in BP and HR regulation. In this thesis, we propose a model-based approach to stability analysis and introduce a quantitative stability indicator of the autonomic-cardiac regulation. We can prevent irregularities in cardiovascular rhythms (e.g., HR and BP) by knowing their causes and developing an intelligent method to control them. An artificial bionic baroreflex can be an effective treatment for baroreflex failure in, for example, individuals with severe orthostatic hypotension. We propose a method to design an artificial bionic baroreflex by mimicking the baroreflex mechanism in the body. This could then be potentially used to adjust existing neurostimulator devices that regulate BP.

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