Prevalence and Pathophysiology of Systemic Arterial Pressure Abnormalities in Childhood Sickle Cell Disease

Overview

It is usually found that the blood pressure of adults with sickle cell disease is lower than in non-sickle cell patients. On the other hand, three recent prospective studies in children with sickle cell disease show prevalence of hypertension diagnosed by ambulatory blood pressure measurement (ABPM) ranging from 32 to 45% but on small numbers of patients (n = 54 at most). This hypertension appears to affect kidney function and has been previously associated with the risk of hemorrhagic stroke. It is therefore important to know the prevalence of hypertension in children with sickle cell disease and to determine its mechanisms. The factors which could explain this high prevalence are the increase in arterial stiffness and the increase in systemic vascular resistance linked to the alteration of the sympathovagal balance contributing to the regulation of vascular tone. Indeed, a disturbance of this balance with an increase in vasoconstrictor sympathetic tone has already been found. Hypothesis: In a subgroup of sickle cell children there is systemic hypertension (prevalence: main objective) linked to the alteration of the sympathovagal balance already established during sickle cell disease (increase in sympathetic tone and decrease in parasympathetic tone) affecting systemic vascular resistance (secondary pathophysiological objectives).

Main objective (200 children): To evaluate the prevalence of elevated blood pressure (former pre-hypertension) and hypertension (including masked hypertension) in children with sickle cell disease. Secondary objectives (60 children): to evaluate the prevalence of loss of nocturnal decrease in blood pressure (dipping); to evaluate arterial stiffness (pulse wave velocity: PWV) and vascular resistance (Augmentation Index, AI) in the different groups: normal, pre-hypertension and hypertension; to evaluate the cardiac sympathovagal balance by studying heart rate variability (HRV) in the three groups: normal, pre-hypertension and hypertension; to evaluate arterial in the three groups: normal, pre-hypertension and hypertension; to evaluate whether the absence of nocturnal dipping is or is not an associated factor of abnormal arterial stiffness, systemic vascular resistance, sympathovagal balance or baroreflex by comparison of subjects with normal dipping versus abnormal dipping.