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Brain Advance Access originally published online on April 27, 2007
Brain 2007 130(6):1631-1642; doi:10.1093/brain/awm071
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© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia

Hwa Kyoung Shin1, Andrew K. Dunn2, Phillip B. Jones3, David A. Boas3, Eng H. Lo4, Michael A. Moskowitz1 and Cenk Ayata1,5

1Stroke and Neurovascular Regulation Laboratory, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, 2Biomedical Engineering Department, University of Texas at Austin, Austin, TX 78712, 3Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, 4Neuroprotection Research Laboratory, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129 and 5Stroke Service and Neuroscience Intensive Care Unit, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA

Correspondence to: Cenk Ayata, Stroke and Neurovascular Regulation Laboratory, Massachusetts General Hospital, 149 13th Street, Room 6403, Charlestown, MA 02129, USA E-mail: cayata{at}partners.org

Normobaric hyperoxia is under investigation as a treatment for acute ischaemic stroke. In experimental models, normobaric hyperoxia reduces cerebral ischaemic injury and improves functional outcome. The mechanisms of neuroprotection are still debated because, (i) inhalation of 100% O2 does not significantly increase total blood O2 content; (ii) it is not known whether normobaric hyperoxia increases O2 delivery to the severely ischaemic cortex because of its short diffusion distance; and (iii) hyperoxia may reduce collateral cerebral blood flow (CBF) to ischaemic penumbra because it can cause vasoconstriction. We addressed these issues using real-time two-dimensional multispectral reflectance imaging and laser speckle flowmetry to simultaneously and non-invasively determine the impact of normobaric hyperoxia on CBF and oxygenation in ischaemic cortex. Ischaemia was induced by distal middle cerebral artery occlusion (dMCAO) in normoxic (30% inhaled O2, arterial pO2 134 ± 9 mmHg), or hyperoxic mice (100% inhaled O2 starting 15 min after dMCAO, arterial pO2 312 ± 10 mmHg). Post-ischaemic normobaric hyperoxia caused an immediate and progressive increase in oxyhaemoglobin (oxyHb) concentration, nearly doubling it in ischaemic core within 60 min. In addition, hyperoxia improved CBF so that the area of cortex with ≤20% residual CBF was decreased by 45% 60 min after dMCAO. Furthermore, hyperoxia reduced the frequency of peri-infarct depolarizations (PIDs) by more than 60%, and diminished their deleterious effects on CBF and metabolic load. Consistent with these findings, infarct size was reduced by 45% in the hyperoxia group 2 days after 75 min transient dMCAO. Our data show that normobaric hyperoxia increases tissue O2 delivery, and that novel mechanisms such as CBF augmentation, and suppression of PIDs may afford neuroprotection during hyperoxia.

Key Words: neuroprotection; laser speckle flowmetry; multispectral reflectance imaging; middle cerebral artery occlusion; acute stroke

Abbreviations: CBF, cerebral blood flow; dMCAO, distal middle cerebral artery occlusion; PID, peri-infarct depolarization

Received October 11, 2006. Revised January 23, 2007. Accepted March 12, 2007.


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