Abstract:

Strokes are the third leading cause of death in western countries, of which 87 % are ischemic. A common treatment is the recanalization of the occluded vessel and therapeutic hypothermia using body surface cooling. The latter is assumed to have a neuroprotective effect, lowering the metabolic rate of the undersupplied tissue and preventing inflammations. However, cooling of the entire body leads to side-effects such as cardiac arrhythmia and organ damage, especially of the lungs. Selective cooling of the carotid blood is a new promising treatment that has the potential to give more control over the cooling, decreasing the side-effects. A temporal and spatial knowledge of the cerebral blood flow and temperature is a necessity for regulating the rate of cooling. Central to the cerebral flow distribution is an arterial circular structure, the circle of Willis. Its redundant collaterals have a compensatory effect in case of ischemia. It varies strongly across patients and underlies anatomical variations, ultimately influencing the compensatory capabilities. In this work, a preexisting hemodynamic model based on the transmission-line approach was extended by a parameterization of patient-specific factors. A simulated study on the cerebral flow was performed, aiming to analyze the parameter sensitivity and interrelations. Stenoses in the M1 segment of the middle cerebral artery (MCA) and the internal carotid artery have been inspected and their respective compensatory mechanisms and influences on said mechanisms were analyzed. In case of a stenosed internal carotid artery (ICA), the mean terminal flow of the anterior cerebral artery (ACA) was reduced from 1.39ml/s to 1.01ml/s, the MCAs from 2.56ml/s to 1.9ml/s. A stenosed M1 segment caused the MCAs flow to be reduced from 2.56ml/s to 0.7ml/s while slightly increasing flow in every other cerebral artery. Anatomical variations, with one or multiple vessels of the circle of Willis (CoW) missing could cause further decrease of terminal vessel flow: up to 14.7 % for a stenosed ICA (missing A1 segment of the other side) and 2.4% for a stenosed MCA (missing P1 segment of the same side and posterior communicating artery (PCoA) of the other side) in regard to the reference mean flow. In case of a stenosed M1 segment, the MCA showed mean flows between 0.18ml/s and 1.34ml/s, depending on the degree of collateralization. This corresponds to a maximum compensation of 53 %. For a stenosed ICA, the collaterals had less effect: depending on the collateralization, the mean flows of the ACA / MCA varied between 0.99ml/s / 1.86ml/s and 1.04ml/s / 1.98ml/s. The model can be personalized according to the specific patient and, in combination with a temperature model, it can be used to monitor the hypothermia of patients suffering from ischemic strokes. The monitoring enables regulating the temperature to appropriate setpoints.