Title: Short Term Regulation in the Cardiovascular System

Speaker: Mette Olufsen, Mathematics

Abstract: 
When standing up, blood is pooled in the legs due to the effect of gravity 
resulting in a drop in systemic arterial pressure and widening of the blood 
flow velocity. This can be modeled by increasing the blood pressure in the 
compartments representing the lower body. To restore blood pressure and 
blood flow velocity a number of regulatory mechanisms are activated. The 
most important mechanisms are autonomic reflexes mediated by the sympathetic 
nervous system and cerebral autoregulation mediated by changes in 
concentrations of oxygen and carbon dioxide. The response to standing is an 
increase in nervous activity, which results in increased heart rate and 
cardiac contractility, vasoconstriction of the systemic arterioles, and 
changes in unstressed volume and venous compliance. The response by the 
cerebral autoregulation is to dilate arterioles in the cerebral vascular 
bed. It is not clear how the autonomic and autoregulation interacts; one 
theory suggests that vasoconstriction, resulting from increased sympathetic 
activity, has an effect throughout the body, but that cerebral vasoconstriction
gets overridden (possibly with a significant delay) by autoregulation 
resulting in a net vasodilatation of the cerebral vascular bed. In this work 
we demonstrate how mathematical modeling can be used to predict the interaction
between autonomic and autoregulation, and to identify sensitive model 
parameters.