 The purpose for this study is to determine if surgery repair of descending thoracic aneurysm causes a temporary decrease in the Blood Brain Barriers ability to remove drugs from the brain back into the blood. The Blood Brain Barrier surrounds the brain and the spinal cord. This Blood Brain Barrier acts as a filter and allows some things to cross into the brain and allows other matter to be removed. Studies have shown the Blood Brain Barrier is affected by inflammation. 