Microvascular Blood Flow in Sickle Cell Anemia

Sickle cell disease is an inherited blood disorder that affects one of every 400 African-Americans newborns in the United States. Sickle cell disease causes the red blood cells to change their shape from a round shape to a half-moon sickle shape. Individuals who have sickle cell disease have a different type of protein that carries oxygen in the blood (hemoglobin) than individuals without sickle cell disease. This different type of hemoglobin makes the red blood cell change into a crescent shape under certain conditions. Sickle shaped cells are a problem because the often get stuck on blood vessels blocking the flow of blood, and cause inflammation and injury to important areas of the body. These symptoms can lead to a painful occurrence called a "sickle cell crisis". Many individuals have to be admitted into the hospital because of the pain caused by a sickle cell crisis. Regadenoson is a drug that may help prevent inflammation and injury caused by the sickle shaped cells. This drug is approved by the FDA to be used as a bolus during a heart stress test in people unable to exercise enough to put stress on the heart by making it beat faster. In a recent Phase I study, a safe dose for regadenoson was determined for adults with sickle cell disease. This dose was given by a slow IV infusion for a 24-48 hour period. Hydroxyurea is the only FDA approved drug for the treatment of sickle cell disease. Hydroxyurea is a pill taken orally and works well but is not useful during a severe sickle cell crisis. In this study researchers will use a new method, contrast-enhanced ultrasound (CEU), to visualize tiny blood vessels in cardiac and skeletal muscle. Changes in CEU measurements before, during and after administration of regadenoson will be examined. Contrast-enhanced ultrasounds will also be performed in individuals who are not having a sickle cell crisis. Some of those individuals will also undergo CEU while they are having a sickle cell crisis to compare those measurements . Lastly CEU results will be compared between individuals with sickle cell anemia and healthy African-Americans. These CEU's will be used to determine if there are changes in the blood flow of tiny blood vessels in certain conditions. This study wants to know if this new method of contrast-enhanced ultrasound will be a useful tool for physicians to use in individuals with sickle cell anemia. The researchers also want to determine if this new method of CEU can be used to reveal if some treatments for sickle cell anemia work better than others.