Figure 1.

Possible mechanisms for increased risk of CI in patients with COPD Owing to cigarette smoke and other noxious environmental substances, reactive oxygen species accumulate in the lungs and trigger local inflammation. The inflammatory mediators in the lungs spill into the plasma and cause systemic inflammation. Inflammatory mediators cross the blood–brain barrier and cause neurodegeneration and reduced synthesis of neurotransmitters, resulting in PD, CI, and AD. Hypoxia also leads to PD due to reduced synthesis of dopamine in the brain. The accumulation of Aβ in the plasma of COPD patients accelerates its deposition in the brain, thus predisposing them to AD and CI. AD: Alzheimer’s disease; Aβ: amyloid-beta; CI: cognitive impairment; COPD: chronic obstructive pulmonary disease; CRP: C-reactive protein; PD: Parkinson’s disease; TNF-α: tumour necrosis factor-alpha.