{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T04:24:40Z","timestamp":1776918280552,"version":"3.51.2"},"reference-count":31,"publisher":"American Physiological Society","issue":"4","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["American Journal of Physiology-Heart and Circulatory Physiology"],"published-print":{"date-parts":[[2003,10]]},"abstract":"<jats:p> The effect of transfusing a nonextravasating, zero-link polymer of cell-free hemoglobin on pial arteriolar diameter, cerebral blood flow (CBF), and O<jats:sub>2<\/jats:sub> transport (CBF \u00d7 arterial O<jats:sub>2<\/jats:sub> content) was compared with that of transfusing an albumin solution at equivalent reductions in hematocrit (\u223c19%) in anesthetized cats. The influence of viscosity was assessed by coinfusion of a high-viscosity solution of polyvinylpyrrolidone (PVP), which increased plasma viscosity two- to threefold. Exchange transfusion of a 5% albumin solution resulted in pial arteriolar dilation, increased CBF, and unchanged O<jats:sub>2<\/jats:sub> transport, whereas there were no significant changes over time in a control group. Exchange transfusion of a 12% polymeric hemoglobin solution resulted in pial arteriolar constriction and unchanged CBF and O<jats:sub>2<\/jats:sub> transport. Coinfusion of PVP with albumin produced pial arteriolar dilation that was similar to that obtained with transfusion of albumin alone. In contrast, coinfusion of PVP with hemoglobin converted the constrictor response to a dilator response that prevented a decrease in CBF. Pial arteriolar dilation to hypercapnia was unimpaired in groups transfused with albumin or hemoglobin alone but was attenuated in the largest vessels in albumin and hemoglobin groups coinfused with PVP. Unexpectedly, hypocapnic vasoconstriction was blunted in all groups after transfusion of albumin or hemoglobin alone or with PVP. We conclude that 1) the increase in arteriolar diameter after albumin transfusion represents a compensatory response that prevents decreased O<jats:sub>2<\/jats:sub> transport at reduced O<jats:sub>2<\/jats:sub>-carrying capacity, 2) the decrease in diameter associated with near-normal O<jats:sub>2<\/jats:sub>-carrying capacity after cell-free polymeric hemoglobin transfusion represents a compensatory mechanism that prevents increased O<jats:sub>2<\/jats:sub> transport at reduced blood viscosity, 3) pial arterioles are capable of dilating to an increase in plasma viscosity when hemoglobin is present in the plasma, 4) decreasing hematocrit does not impair pial arteriolar dilation to hypercapnia unless plasma viscosity is increased, and 5) pial arteriolar constriction to hypocapnia is impaired at reduced hematocrit independently of O<jats:sub>2<\/jats:sub>-carrying capacity. 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