Microfluidic assessment of PO2-regulated RBC capillary velocity in ME/CFS

• PO 2 -regulated RBC capillary velocity is impaired in ME/CFS. • RBC velocity response to PO 2 is a unique characteristic in ME/CFS. Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex disease of unknown etiology that affects multiple organ systems. Although there is no established treatment or diagnostic test for ME/CFS yet, studies have consistently demonstrated impaired cerebral blood flow (CBF) and blood flow regulation in ME/CFS. In this study, we measured red blood cell (RBC) velocity in microfluidic capillaries at varied oxygen tensions (PO 2 ) and showed that, compared to RBCs from heathy controls, RBCs from patients with ME/CFS exhibit compromised capillary velocity in response to reduced PO 2 . To examine whether such PO 2 -regulated RBC capillary velocity could be used to assess or diagnose ME/CFS, we conducted receiver operator characteristic analysis and used machine learning to analyze various features of PO 2 -regulated RBC capillary velocity. We found that velocity slope–based classifiers were highly accurate, sensitive, and specific (ie, 77.8%, 76%, and 90%, respectively) in ME/CFS classification. Furthermore, we demonstrated this RBC-based microfluidic approach can be used to evaluate potential drugs (ie, salmeterol xinafoate and xanomeline) for improving RBC capillary velocity in ME/CFS. These findings highlight previously unrecognized roles of RBCs in the pathophysiology of ME/CFS and suggest a potential RBC-based test for ME/CFS diagnosis.