Angiotensin converting enzyme inhibitors (ACE-I) are a group of blood pressure-lowering medicines. Some studies suggest that ACE-I, such as ramipril, may help prevent Alzheimer's disease (AD). The purpose of the research is to see how ramipril affects a substance in the body called beta-amyloid. Beta-amyloid is found in the brain and in the liquid around the brain and spinal cord. High amounts of beta-amyloid may be associated with a greater risk of getting Alzheimer's disease. This study will see if ramipril can lower the amount of beta-amyloid in the spinal fluid. This study will also see if ramipril affects blood vessel function and memory and thinking. The investigators hope that future studies will show whether ramipril might prevent memory loss and decrease the chance of developing Alzheimer's disease.