Diameters of blood vessels measured with intravital microscopy. Arteriole (A) and venule (B) diameters measured at baseline; after administration of saline, apoHb, or apoHb-Hp; and after 20% isovolemic exchange transfusion of PolyHb. Top panels show the measured values; bottom panels show values normalized to the baseline of the same vessel in the same animal. Gray lines connect measurements obtained in the same blood vessel. *P < .05 compared between groups. ^aP < .05 compared with the saline administration group at the same time point. n = 5 animals per group, 6 vessels per animal.