 Transfusion of red blood cells is often used in critically ill patients with low red blood cell counts to prevent disease progression and death. Recent studies suggest that the use of aged versus fresh red blood cells are associated with worse clinical outcomes. There is evidence that red blood cells work with the cells lining our blood vessels to produce a variety of substances that normally cause arteries to relax and increase blood supply. Two of these substances are called nitric oxide NO and endothelium-derived hyperpolarizing factor EDHF. The investigators are trying to determine the nature of these substances in human beings when they are transfused aged versus fresh red blood cells. The purpose of the study is to test the effects of transfusing aged versus fresh red blood cells in volunteers with traditional cardiovascular risk factors high blood pressure, diabetes, high cholesterol, and tobacco use on 1 the degree of relaxation in the arteries and subsequent changes in blood flow, 2 blood levels of oxidant molecules, 3 inflammation, and 4 stem cells. 