Hyperbaric oxygen decreases infarct size and behavioral deficit after transient focal cerebral ischemia in rats

Cerebral hypoxia is a major component of immediate and secondary cell damag e caused by ischemia. Hyperbaric oxygen (HBO) is a potent means to increase the amount of oxygen dissolved in blood plasma. The effectiveness of HBO i n clinical and experimental cerebral ischemia, however, is controversial. W e sought to determine whether treatment with HBO initiated early after foca l cerebral ischemia-onset protects the brain when experimental conditions s uch as brain temperature are controlled. Male Wistar rats (n = 57) underwen t reversible filament occlusion of the right middle cerebral artery (MCA) f or 75 min. Animals were awakened after filament introduction and assessed f or presence of forelimb paresis. Rats then underwent a 60-min course of eit her 100% O-2 at 1.0 atmosphere absolute (ata; control group), HBO 1.5 ata, or HBO 2.5 ata in a customized HBO chamber allowing physiological monitorin g and pericranial temperature control. The filament was then removed. Seven days after ischemia, rat behavior was scored from 3-18 (18=normal) and bra ins were removed for histological analysis of infarct volume. Rats treated with HBO 2.5 ata had better mean +/- standard deviation (S.D.) behavioral s cores (14 +/- 2; p < 0.05) than control (10 +/- 3) or HBO 1.5-ata-treated a nimals (11 +/- 3). Similarly, total infarct volumes (mean I S.D.) were smal ler in animals receiving HBO at 2.5 ata (76 +/- 65 mm(3); p < 0.05) compare d to control (129 +/- 83 mm(3)) and HBO 1.5-ata (119 +/- 68 mm(3))-treated groups. Cortical infarction occurred less frequently in HBO 2.5-ata-treated than in control animals (44% vs. 71%; p < 0.05), We conclude that HBO can improve outcome after temporary focal ischemia when treatment is started ea rly after ischemia-onset but HBO dose appears important. Potential mechanis ms include enhanced oxygen supply to marginally perfused cells. (C) 2000 El sevier Science B.V. All rights reserved.