Delayed and multiple hyperbaric oxygen treatments expand therapeutic window in rat focal cerebral ischemic model

Although the brain-protective effect of single, early applications of hyperbaric oxygen (HBO) has been reported in acute ischemic stroke models, few studies have reported the long-term effect--especially after multiple HBO applications. This study employed delayed, multiple HBO treatments and evaluated cerebral infarction and neurological functional recovery for 4 weeks after transient focal ischemia. Adult male Sprague-Dawley rats were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) and were subsequently exposed to HBO (2.5 atmospheres absolute [ATA]) for 2 hours per day. HBO was administered at either 6 or 24 hours after MCAO/R and was repeated daily for 6 days. Rat behavior was scored to evaluate neurological deficits. The brains were removed for histological analysis of the infarct ratio at 1 and 4 weeks. Rats with HBO delayed for 6 or 24 hours following MCAO/R displayed a significant decrease of infarct ratio and amelioration of neurological deficits compared to the untreated group. This study suggests that delayed, but multiple, HBO treatments can improve neurological evaluation and reduce cerebral infarction.