Abstract There is a lack of reliable methods of evaluation of brain ischemic injury in patients undergoing cardiac surgery. The present study was, therefore, planned to evaluate whether serum S100β protein (I), brain cortical microdialysis (II), intracranial pressure (III) and electroencephalography (EEG) (IV) are predictive of postoperative death and brain ischemic injury in an experimental surviving porcine model of hypothermic circulatory arrest (HCA). One hundred and twenty eight (128) female, juvenile (8 to 10 weeks of age) pigs of native stock, weighing 21.0 to 38.2 kg, underwent cardio-pulmonary bypass prior to, and following, a 75-minute period of HCA at a brain temperature of 18°C. During the operation, hemodynamic, electrocardiograph and temperature monitoring was performed continuously. Furthermore, metabolic parameters were monitored at baseline, end of cooling, at intervals of two, four and eight hours after HCA and before extubation. Electroencephalographic recording was performed in all animals, serum S100β protein measurement in 18 animals, cortical microdialysis in 109 animals, and intracranial pressure monitoring in 58 animals. After the operation, assessment of behavior was made on a daily basis until death or elective sacrifice on the seventh postoperative day. All four studies showed that these parameters were predictive of postoperative outcome. Animals with severe histopathological injury had higher serum S100β protein levels at every time interval after HCA. Analysis of cortical brain microdialysis showed that the lactate/glucose ratio was significantly lower and the brain glucose concentration significantly higher among survivors during the early postoperative hours. Intracranial pressure increased significantly after 75 minutes of HCA, and this was associated with a significantly increased risk of postoperative death and brain infarction. A slower recovery of EEG burst percentage after HCA was significantly associated with the development of severe cerebral cortex, brain stem and cerebellum ischemic injury. In conclusion, serum S100β protein proved to be a reliable marker of brain ischemic injury as assessed on histopathological examination. Cerebral microdialysis is a useful method of cerebral monitoring during experimental HCA. Low brain glucose concentrations and high brain lactate/ glucose ratios after HCA are strong predictors of postoperative death. Increased intracranial pressure severely affected the postoperative outcome and may be a potential target for treatment. EEG burst percentage as a sum effect of anesthetic agent and ischemic brain damage is a useful tool for early prediction of severe brain damage after HCA. Among these monitoring methods, brain cortical microdialysis seems to be the most powerful one in predicting brain injury after experimental hypothermic circulatory arrest.

Ventricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta. Currently, the implantation angle of the VAD cannula is not taken into consideration. Since the VADs supply a significant amount of blood flow to the aorta, the implantation angle can greatly affect the trajectory of the formed thrombi as well as the cardiac flow field inside of the aortic arch. This study aims to vary the implantation angle of a pediatric Left Ventricle Assist Device (LVAD) through a series of computational fluid dynamics (CFD) software simulations focusing on the aortic arch and its branching arteries of a 20 kg pediatric patient in order to reduce the occurrence of stroke.

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ABSTRACT Left Ventricular Assistant Devices (LVAD's) have been routinely used to treat patients with heart failure, and to help bridge patients awaiting heart transplant surgery. A major problem with LVAD's is their tendency to stimulate the formation of blood clots that can cause serious conditions such as strokes, thrombosis, and even death. A study on an alternative aortic bypass for patients with LVAD implants as a mean to reduce the number of thrombi that eventually flow into the carotid arteries by promoting them to flow into the subclavian arteries and descending aorta is presented. The study consists of Computational Fluid Dynamics (CFD) models for standard and alternative aortic bypass L V AD configurations. Results show that thrombi with diameters in the range of 2mm to 5mm have the highest chance of flowing into the carotid arteries from the aortic arch. The CFD study of the alternative aortic bypass implementation shows an increase in the number of thrombi that flow out of the aortic arch to the descending aorta by 4.65% for 0.5mm diameter, 11.63% for 2mm diameter, 37.21 % for 3mm diameter, and 9.3% for 5mm diameter thrombi.

Transcatheter aortic heart valve replacement (TAVR) is a procedure to replace a failing aortic valve and is becoming the new standard of care for patients that are not candidates for open-heart surgery [2]. However, this minimally invasive technique has shown to cause ischemic brain lesions, or “silent infarcts”, in 90% of TAVR patients, which can increase the patient’s risk for stroke by two to four times in future years [3]. Claret Medical Inc., a medical device company, has developed a cerebral protection system that filters and captures embolic debris released during endovascular procedures, such as TAVR. This thesis utilized CT scans from Claret Medical to create a physical construct of the aortic arch to experimentally validate a theoretical computer model through flow visualization. The hypothesis was that the empirical model can accurately mimic the fluid dynamic properties of the aortic arch in order validate an in silico model using the finite elements program COMSOL MultiPhysics® Modeling Software. The physical model was created from a patient CT scan of the aortic arch using additive manufacturing (3D printing) and polymer casting, resulting in the shape of the aortic arch within a transparent, silicone material. Fluid was pumped through the model to visualize and quantify the velocity of the fluid within the aortic arch. COMSOL MultiPhysics® was used to model the aortic arch and obtain velocity measurements, which were statistically compared to the velocity measurements from the physical model. There was no significant difference between the values of the physical model and the computer model, confirming the hypothesis. Overall, this study successfully used CT scans to create an anatomically accurate physical model that was validated by a computer model using a novel technique of flow visualization. As TAVR and similar procedures continue to develop, the need for experimental evaluation and visualization of devices will continue to grow, making this project relevant to many companies in the medical device industry.

No description available.