Non-linear parameter estimation of volume sensitivity of the coronary resistance in the isolated canine septum

Common parameters to describe the coronary circulation are resistances (Rs) and capacitances (Cs). In six isolated, maximally dilated, perfused, non-contracting canine interventricular septa, the Rs and Cs at different pressure levels were estimated by obtaining the inflow-pressure transfer functions (Q/P) and volume-pressure transfer functions (T/P). To interpret the data, simple lumped two compartment RCR models were fitted. Models with fixed resistances could not fit simultaneously Q/P and T/P. Therefore models with volume dependent parameters were tested as well. However, these models had more parameters, which could not be uniquely identified from the data. Many parameter sets, which predicted adequate transfer functions, were created. After comparing these parameter sets, it was concluded that the first resistance and the first capacitance could be estimated, furthermore a relation between the distal capacitance and the volume sensitivity of the third resistance was found: the higher the capacitance, the lower the sensitivity