Salmeterol and xanomeline improved PO₂-regulated RBC capillary velocity and sensitivity in ME/CFS. (A) RBCs treated with 1 nM salmeterol exhibited the highest magnitude and sensitivity of PO₂-regulated capillary velocity (patients with ME/CFS, n = 9; 955, 956, and 473 cells for 0 nM (R² = 0.81), 1 nM (R² = 0.91) and 10 nM salmeterol (R² = 0.85), respectively. Calculated slope of –0.098 ± 0.0331, –0.175 ± 0.0485, and –0.149 ± 0.0121 mm/s per mm Hg for 0, 1, and 10 nM salmeterol, respectively. ns, P > .05 (Mann-Whitney test). (B) Xanomeline incubation increased the magnitude and sensitivity of PO₂-regulated RBC capillary velocity (patients with ME/CFS, n = 8; 905, 690, and 917 cells for 0-μM (R² = 0.92), 1-μM (R² = 0.91), and 10-μM xanomeline (R² = 0.91), respectively. Calculated slope (mm/s per mm Hg) of –0.083 ± 0.0381, –0.204 ± 0.0730, and –0.292 ± 0.0478 for 0, 1, and 10 μM, respectively. ns, P > .05 (Mann-Whitney test); ∗∗P < .01 (unpaired t test). Each data point in calculated slope represents 1 participant. Data are presented as mean ± SEM.