Abstract:

Stroke is the third-most widespread cause of death in western countries. 87 % of them are ischemic strokes. The current standard therapy often involves the placement of a catheter into the affected artery. Simultaneously, hypothermia of the whole body is exercised, which slows down the metabolism of the entire human body. A new promising therapy is currently developed. It involves a cooling catheter that is placed into the common carotid artery. The catheter cools the blood flow into the affected area. However, during the therapy it is not possible to measure the cerebral temperatures without further harm for the patient. The temperatures therefore need to be simulated in a computational model, which includes most of the human arterial system. The currently used hemodynamic model included detailed arterial structures of the arms and the torso, which captured ~35 % percent of the model. However, these parts were not relevant for the temperature simulation in the cerebral region. The hypothesis was, that the arterial structures of the arms and the torso can be modeled in a more efficient way without losing cerebral influence during a stenosis. Therefore, an alternative for the modeling of these parts was desired. The chosen replacement for the arterial structures was the three element Windkessel (WK) model. The modeling of the WK was done using equation based modeling. The differential equations of the WK were implemented consistent with the current model using C code in s-function blocks of Simulink. The WK were then connected to the model at the corresponding segments. The replacements reduced the model by 304 parameters, which equals around a third of the former model. The adaption influenced the flow curves and the average flow into the replaced structures and in the cerebral region. The change in average flow rates was smaller than 5 %. After the adaption, the elements of the WK were optimized using a trust region reflective optimization, which was conducted in Matlab (lsqnonlin). The optimization improved the curve forms of the flows into the replaced arterial structure. Additionally, a sensitivity analysis of the WK parameters was executed. The results showed, that the resistors inside the Windkessel model had the highest influence. However, this influence was very small. In the end, the influence of a stenosis on the adapted model was executed and evaluated. The influence of a stenosis on the average flow into the replaced arterial structures did not change. In conclusion, the replacement had a neglectable influence on the hemodynamic model. The optimization improved the outcome of the flow curves and the sensitivity analysis showed, that the parameters do not significantly change the characteristics of the model. In the future, the outcome of the adaption can be further evaluated and the optimization could be further extended.