**Arterial Function Parameters and Transcranial Doppler Velocity in Pediatric Patients With Sickle Cell Disease** Sickle cell disease affects the arteries which are blood vessels that carry blood away from the heart. In this study, researchers want to see if there are differences in artery function between two groups of children with sickle cell disease. One group has normal blood flow speed in the brain (measured by transcranial Doppler velocity) and no history of stroke, while the other group has abnormal blood flow speed, with or without a stroke history. The study aims to compare the artery function in these groups by checking blood pressure and other health markers. *Key Points:* - **Study Length**: Participants will undergo measurements, but there's no long-term follow-up. - **Visits Needed**: Only one visit to the Sickle Cell Unit in Kingston, Jamaica is required for the measurements. - **Risks and Compensation**: There are no specified risks or compensation mentioned. **Eligibility**: Children aged 4-16 with sickle cell disease are eligible, but they must not have received a blood transfusion in the last two months or be currently ill. Parents and guardians must provide consent for participation.