The time window of intermittent hypoxia intervention after middle cerebral artery occlusion.

It was known that preconditioning hypoxia can reduce the damage caused by ischemia. However, there was no study investigating the effects of intermittent hypoxia post ischemia. The purpose of this study was to investigate the time window for administering the hypoxia for beneficial effects after cerebral ischemic damage. According to the recovery days post transient middle cerebral occlusion (MCAO), the rats were randomly assigned to one of the 4 groups (n = 20 for each group, I, II, III, and IV). Rats were then assigned to one of the 2 subgroups (a and b). Rats in group Ia, IIa, IIIa, and IVa were exposed to 7 days of intermittent hypoxia (12% O2 for 4 hours per day) after recovery 1, 2, 3, and 7 days from MCAO, respectively. Rats in group Ib, IIb, IIIb, and IVb rested for 7 days in the same hypoxia chamber without hypoxia exposure after 1, 2, 3, and 7 days post MCAO, respectively. The mortality rate of rats received hypoxia after 1 day' and 2 days' recovery post MCAO was 40% (P = 0.087) and 10% (P = 0.5), respectively. The mean infarct volume of rats received hypoxia after 7 days' recovery was significantly less than that of the comparable control group (9.23 +/- 0.71% vs. 13.32 +/- 1.26%; P = 0.013), and no rats died in this group. In summary, intermittent hypoxia intervention for 7 days after 7 days of recovery post ischemia can reduce the infract volume, and does not increase the mortality rate. According to our results, we suggest that 7 days post ischemia may be the suitable time to begin the intermittent hypoxia intervention to enhance the recovery from cerebral ischemia.