In vivo effects of Hb solutions on blood viscosity and theologic behavior of RBCs: comparison with clinically used volume expanders

BACKGROUND: Hb-based oxygen carriers (HbOCs) have vasoactive effects that a re still poorly understood. Factors known to have vasoactive effects, such as plasma, whole-blood viscosity, and the theologic behavior of RBCs, are m odulated by HbOCs in vitro, but few in vivo studies have been performed. STUDY DESIGN AND METHODS: Rabbits were phlebotomized (30%) and resuscitated with unmodified stroma-free Hb (SFHb), dextran-tetracarboxylate-Hb (Dex-BT C-Hb), O-raffinose-polymerized Hb (OrpHb), HSA, or hydroxyethyl starch 200 (HES). Plasma viscosity was assessed with a capillary viscometer and whole- blood viscosity with a rotational viscosimeter. RBC aggregation kinetics we re determined by analysis of back-scattered light in a rotating device. RESULTS: As compared to that in the control RBC suspension, resuscitation w ith SFHb, OrpHb, or HSA decreased plasma and whole-blood viscosity as well as RBC aggregation; resuscitation with Dex-BTC-Hb increased whole-blood vis cosity at low shear rates as well as RBC aggregation, whereas that with HES decreased whole-blood viscosity but increased RBC aggregation. CONCLUSION: HbOCs have different theologic effects in vitro and in vivo. Th ere are marked differences among the Hb solutions in their in vivo effects on viscosity and RBC theologic behavior (especially at low shear rates enco untered in the venous circulation and the microcirculation), which may be r elated to the chemical modifications applied to hemoprotein. These results could contribute to an understanding of the vasoactive effects of HbOCs.