Children's National

for Subjects with Sickle Cell Disease in Pain Crisis: 1. Age 6 to 21 years old. 2. Diagnosis of sickle cell anemia: a. Diagnosis of sickle cell disease (electrophoresis or HPLC documentation of hemoglobin SS, SC, S-beta-thalassemia or other hemoglobinopathies causing sickle cell disease is required). 3. Acute onset pain crisis in a distribution typical for that subject, onset within the last 7 days and for which hospitalization and parenteral narcotic pain treatment are required. 4. Ability to provide informed written consent.

for Subjects with Sickle Cell Disease in Pain Crisis: 1. Pregnancy. 2. History of non-trivial injury, burns, surgery or skin ulcers on the arms. 3. Fever or suspected sepsis at time of pain crisis 4. Administration of any of the following drugs within the last 14 days: - Phosphodiesterase-5 inhibitors (sildenafil, vardenafil, tadalafil) - Endothelin-1 receptor blockers (bosentan, sitaxentan, ambrisentan, tezosentan) - Nitric oxide donors (nitroglycerin, nitroprusside, nitrates) 5. Ingestion of caffeine within the 12 hours before the start of the study appointment, or tobacco use within the 30 days before the study appointment. 6. Diagnosis with any of the following chronic diseases or conditions: - History of high blood pressure - History of high cholesterol - History of diabetes - History of chronic kidney disease (serum creatinine must not be greater than 2 mg/dL) - History of coronary artery disease or peripheral vascular disease 7. Received a blood transfusion within 7 days of the study procedure. Inclusion Criteria for Subjects with Sickle Cell Disease in Steady State: 1. Age 6-21 years 2. Diagnosis of sickle cell disease (electrophoresis or HPLC documentation of hemoglobin SS, SC, S-beta-thalassemia or other hemoglobinopathies causing sickle cell disease is required). 3. Ability to provide informed written consent. Exclusion Criteria for Subjects with Sickle Cell Disease in Steady State: 1. Pregnancy. 2. History of non-trivial trauma, burns, surgery or skin ulcers on the arms. 3. Fever or suspected sepsis at time of pain crisis 4. Experience of an acute pain crisis requiring intravenous (IV) narcotics and hospital admission within the last 14 days. 5. Ingestion of caffeine within the 12 hours before the start of the study appointment, or tobacco use within the 30 days before the study appointment. 6. Administration of any of the following drugs within the last 14 days: - Phosphodiesterase-5 inhibitors (sildenafil, vardenafil, tadalafil) - Endothelin-1 receptor blockers (bosentan, sitaxentan, ambrisentan, tezosentan) - Nitric oxide donors (nitroglycerin, nitroprusside, nitrates) 7. Diagnosis of any of the following chronic diseases or conditions: - History of high blood pressure - History of high cholesterol - History of diabetes - History of chronic kidney disease (serum creatinine must not be greater than 2 mg/dL) - History of coronary artery disease or peripheral vascular disease 8. Received a blood transfusion within 7 days of the study procedure.