Under deoxygenated conditions, sickle blood rheology is differentially affected by fluid admixtures with opposing tonicities. (A) Representative rheological plot of whole sickle blood resuspended in a fluid (fluid with final sodium = 141 mEq/L shown). Blood velocity (red dots, left side y-axis) responds to changes in oxygen tension (blue dots, right side y-axis). Blood velocity exponential deceleration rates were calculated by fitting the deoxygenated blood velocity region to an exponential decay function (dashed black line, equation). (B) Deceleration rates for blood samples were calculated from N = 10 patients with SCD. Samples exposed to admixtures with sodium concentrations of 141 mEq/L were significantly higher than blood samples exposed to sodium concentrations of 103 mEq/L.