The oxygen-hemoglobin dissociation curve A. Flattened upper portion 100 B Steep middle portion 290 E80 C. Lower portion g 70 saturation 60 (mm Hg) f Hb 13.5 s50 20 35 30 40 40 75 50 83.5 o30 60 89 芒 70 92.7 d20 80 94.5 90 96.5 10 100 97.5 20 60 80100 Po,(mm Hg)10 The oxygen-hemoglobin dissociation curve A. Flattened upper portion B. Steep middle portion C. Lower portion