Exploring Near Infrared Spectroscopy (NIRS) technologies for assessment of muscle physiology, tissue oxygenation, and blood flow in patients with Sickle Cell Disease (SCD

National Heart, Lung, And Blood Institute

Investigators

Abstract

Sickle cell disease (SCD) is an inherited hemoglobinopathy that disproportionately impacts minority populations in the United States affecting about 100,000 individuals, primarily of African ancestry, and 1 in 365 African-American births. The substitution of valine by glutamic acid on the 6th amino-acid of beta globin results an abnormal hemoglobin variant (HbS) which polymerizes once deoxygenated, and alters both the structure and function of red blood cells (RBCs) distorting them into bizarre sickle shapes. Sickled RBCs have a lifespan 1/6th that of normal, resulting in chronic hemolytic anemia; they are also rigid and can obstruct microvascular blood flow causing recurring, unpredictable cycles of acute vaso-occlusive pain, commonly referred to as vaso-occlusive crises (VOC). The recurrent VOCs lead to hypoxia-reperfusion injury and together with the intravascular hemolysis promote inflammation and vascular endothelial damage. This systemic vasculopathy affects multiple organs leading to cardiovascular complications, chronic pain, cerebral and kidney impairment. Near infrared spectroscopy (NIRS) is a non-invasive optical technique for characterizing microvascular hemodynamics including hemoglobin concentration, blood flow, and tissue oxygen saturation. There is a wealth of literature reporting on NIRS in a wide variety of clinical applications including breast cancer and exercise science. Given the impairments to microvascular flow and endothelial dysfunction associated with SCD, advanced quantitative NIRS is an attractive candidate to provide comprehensive hemodynamic evaluations in point-of-care settings. There are limited studies evaluating NIRS devices in SCD. One study has reported a relatively dampened hyperemic response after brachial cuff occlusion, indicative of endothelial dysfunction in SCD patients. The preliminary data obtained from another research study are encouraging and demonstrates that hemodynamic information collected correlates with clinical lab values. In this single site, non-interventional, exploratory study, 40 subjects (20 SCD (HbSS and/or HbSB0) and 20 healthy controls (HbAA)) will undergo a baseline hemodynamic assessment as outpatients utilizing NIRS applications and protocols. A subset of study participants may be invited to return to the Clinical Center for clinical and NIRS reassessment periodically for a maximum of 4 additional visits, at least 3 days apart, within 120 days from their initial (baseline) visit to test for repeatability of the NIRS. The purpose of this study is to generate further NIRS-derived tissue hemodynamic data in SCD compared to data from healthy controls. The data will help inform the most appropriate and efficient optical technique that best differentiate the abnormal hemodynamics in SCD patients from normal physiological variation in healthy controls. The optimal NIRS technique can then be adopted and applied for regular screening and disease monitoring in SCD patients. Enrollment has been completed, with a total of 40 subjects (20 SCD and 20 HbAA) who have completed participation in this trial.