Stiffness the model

The decision process of putting together models based the above methods is helped by some observations about timescale and solution stiffness. The modeler should decide on a timescale of interest. The characteristic times, or first order time constants, for a typical flow and a pressure element based on lumped momentum and mass conservation respectively are shown in the following equations [7, 8] ... 

If no flexible joints are considered (in between the P and S systems they represent), the absence of collaboration with the P system is not judicable by means of qualitative considerations, but it can require a structural analysis of the PS system including them as structural elements. In this case, the designer can follow some suggestions such as those included in CEN (2008) that consider a structural system as SE if its global stiffness is lower than 15 % of the P system stiffness. The models concerning the infilled frames systems are well known. 

The same ventricle may be coupled to a pathological arterial system, for example, one with increased peripheral resistance or altered arterial stiffness. The model s flexibility allows the description of heart pathology as well as changes in blood vessels. This one equation (Equation 17.8) with one set of measured parameters can characterize the fundamental mechanical properties of the heart, as follows [49]. 

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