Chronic cerebral ischemia (CCI) is viewed as an alarming state induced by long-term reduction in cerebral perfusion, which is associated with neurological deficits and high risk of stroke occurrence or recurrence. CCI accounts for a large proportion in both outpatient and inpatient subjects with cerebrovascular disease, while the treatment of CCI remains a formidable challenge to clinicians. Normobaric oxygen (NBO) is an adjuvant hyper-oxygenation intervention supplied with one atmosphere pressure (1ATA=101.325kPa). A plethora of studies have demonstrated the efficacy of NBO on the penumbra in acute stroke. NBO has been shown to increase oxygen pressure, raise intracranial blood flow, protect blood-brain barrier and enhance neuro-protective effects. As the similar underlying mechanisms shared by the penumbra in stroke and the ischemic-hypoxic brain tissues in CCI, the investigators speculate that NBO may serve as a promising therapeutic strategy for attenuating short-term symptoms or improving long-term clinical outcomes amongst patients with CCI. Due to the scant research exploring the efficacy of NBO for treating CCI so far, the clinical studies are warranted to verify this hypothesis urgently.