Analog Simulation of Aortic Stenosis

In cardiovascular physiology mathematical and analog simulations are well known (Beneken, 1965; Defares et al.; 1963, Grodins; 1959; Kordaš et al., 1968; Milhorn, 1966; Osborn,1967;). However, in analog modelling physical electrical models have been replaced by computer analysis of electronic analog circuitry. Then they have been applied to various physiological systems (Bošnjak & Kordaš, 2002; Dolenšek et al., 2005), to study also cardiovascular physiology (Rupnik et al., 2002), including mechanisms of compensation (Podnar et al., 2002) and principles of homeostasis, i. e. negative feedback mechanisms (Podnar et al., 2004). Recently, the equivalent circuit simulating the cardiovascular system was further upgraded to simulate, as close as possible, conditions in man in vivo. First, the intrathoracic pressure was made slightly negative and undulating at the rate of respiration. Second, the homeostasis included not only a control of venous tone and contractility of left and right ventricle, but also the control of heart rate. Third, the mean arterial pressure was in some conditions reset from the normal to a higher operating level (simulating increased sympathetic tone). By using these approaches recently various clinical conditions were simulated: acute left ventricle failure (myocardial infarction), aortic stenosis and exercise in man with aortic stenosis (Sever et al., 2007), and consequences of aortic and of mitral regurgitation (Dolenšek et al., 2009). In present simulations it is attempted to extend both recent simulations quoted above. The consequences, induced by exercise in patients with aortic stenosis are to be studied in more detail. To meet this end, in aortic stenosis i) the aortic and mitral flows are studied and ii) mechanism of exhaustion, induced by exercise, are simulated.