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Increased arterial oxygen content by artificial haemoglobin induces a decrease in regional cerebral blood flow and
Michael Schöler1, Christian Lenz, Wolfgang Kuschinsky
1Clinic for Anesthesiology and Critical Care Medicine, Medical Faculty Mannheim, Germany.
High hemoglobin concentration reduced regional cerebral blood flow (CBF) in rats, even at normal hematocrit. This suggests that elevated hemoglobin can impair local oxygen delivery to specific brain regions.
Area of Science:
- Physiology
- Neuroscience
- Hematology
Background:
- Cerebral oxygen delivery is normally maintained by adjusting cerebral blood flow (CBF) to match oxygen content.
- Previous studies induced regional CBF decreases via higher oxygen content under hyperbaric or hyperviscous conditions.
- This study investigated if high hemoglobin concentration alone, at normal hematocrit, reduces local CBF.
Purpose of the Study:
- To determine if elevated hemoglobin concentration, independent of hematocrit, affects regional cerebral blood flow (CBF).
- To assess the impact of high hemoglobin on local cerebral oxygen delivery under normal physiological conditions.
Main Methods:
- Conscious rats underwent isovolemic plasma exchange with hemoglobin-based oxygen carriers to achieve high hemoglobin (19 g dL−1) at normal hematocrit.
- A separate group had hematocrit reduced via exchange with a hemoglobin-based oxygen carrier, maintaining normal hemoglobin levels.
- Mean and regional CBF were measured using iodo-[(14)C]-antipyrine autoradiography; oxygen delivery was calculated.
Main Results:
- Mean CBF was significantly reduced (23%) in rats with high hemoglobin (20.3 g dL−1, Hct 0.44) compared to controls (15.3 g dL−1, Hct 0.44).
- Regional CBF decreased in 22 of 39 brain regions under high hemoglobin conditions.
- While overall cerebral oxygen delivery remained constant, high hemoglobin reduced local oxygen delivery in one-third of brain structures.
Conclusions:
- Elevated arterial hemoglobin concentration can decrease regional cerebral blood flow.
- High hemoglobin levels, even at normal hematocrit, can impair local oxygen delivery to specific brain regions.
- Overall cerebral oxygen delivery is maintained, but regional distribution is affected by high hemoglobin.
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