Effects of free and liposome-encapsulated hemoglobin on choroidal vascularplexus blood flow, using the rabbit eye as a model system

Purpose. This study investigated the vasoconstrictive effects of both strom a-free and liposome-encapsulated cross-linked hemoglobin (Hb) on vascular p lexus hemodynamics, using the choroid of the rabbit eye as a model system. Methods. Sequential subfraction of high-speed ICG fluorescence angiogram im ages facilitated visualization of the time-varying patterns of blood flow d istribution in the choriocapillaris during the cardiac cycle. Differences b etween baseline and post-hemoglobin injection blood flow distributions were analyzed. Likewise, differences in the time-varying patterns of flow distr ibution between the particulate and liquid phases of blood during a cardiac cycle were investigated, since this may bear on differences in vasoactivit y induced by circulating stroma-free vs. encapsulated Hb. Results. Cross-linked Hb induced a transient, but marked, localized reducti on in choriocapillaris blood flow. This effect was significantly attenuated when liposome encapsulated cross-linked hemoglobin was administered. Plexu s blood flow distribution was different for particulate and liquid ICG. Conclusions. Differences in particulate and liquid ICG flow patterns sugges t that one contribution to the different plexus blood flow patterns observe d in the encapsulated and free Hb experiments may be due to differences in liquid and particle-bound Hb distribution within the plexus. The observed c horiocapillaris blood flow reductions may be attributable to an aggregate e ndothelial cell contractility induced by presence of extra-cellular Hb in t he choriocapillaris plexus.