Measurement of the Reactive Hyperemia Index in Sickle Cell Patients During Pain Crisis and After Recovery

Severe recurrent pain is the most common cause of acute morbidity in sickle cell disease1. The underlying pathogenesis was initially thought to be ischemia from obstruction of capillary beds by stiffened red blood cells; however, there is evidence that other factors contribute to the pathogenesis of sickle cell pain crisis, such as inflammation and coagulation, ischemia-reperfusion injury, angiogenesis balance, and vasomotor tone processes that are regulated by endothelial nitric oxide.

Recent clinical data suggest that subjects with sickle cell disease suffer from chronically impaired nitric oxide bioavailability. This has been attributed to increased consumption of nitric oxide by hemoglobin and reactive oxygen species, or decreased production of nitric oxide by endothelial cells; however the roles of nitric oxide bioavailability and endothelial dysfunction during acute pain crisis are controversial and incompletely understood. Although there have been several studies of endothelial function in steady state sickle cell disease, there has been no comprehensive study of endothelial function during pain crisis.

In this study, our primary objective is to measure the reactive hyperemia index (a measure of the endothelial response to shear stress) in twenty sickle cell subjects during acute pain crisis and to compare it with the reactive hyperemia index measured after recovery from pain crisis. This will identify whether there are acute changes in endothelial cell function during sickle cell pain crisis. Our secondary objective is to compare the reactive hyperemia index of thirty-five sickle cell subjects in steady state versus the reactive hyperemia index of thirty-five healthy control subjects. This will identify whether there are chronic differences in endothelial function between sickle cell subjects and healthy control subjects.

This study will determine if there are defects in endothelium-dependent vasodilation in response to shear stress during sickle cell pain crisis. Moreover, this study provides an opportunity to evaluate new physiologic biomarkers of sickle cell pain crisis based on measurements of blood flow, temperature, and oxygenation in the skin. These measurements may serve as clinical endpoints in future studies of disease pathogenesis or therapeutic interventions for sickle cell disease.