Breathing oxygen at higher than normal partial pressure, leading to hyperoxia, can cause oxygen toxicity or oxygen poisoning. The central nervous system, lungs, and eyes are the systems primarily affected...Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes leading to the collapse of the alveoli in the lungs, retinal detachment and retrolental fibroplasia in the eye, and seizures.
ncbi.nlm.nih.gov
...The ‘wash-out’ of carbon dioxide progresses, from the lungs, and hence from the blood, and from the body tissues including, importantly, the brain. Carbon dioxide is a crucial variable in acid–base homeostasis; its reduction shifts the body fluids towards greater alkalinity (increased pH) and this has further knock-on effects. For one thing, it tends to cause constriction of some blood vessels, particularly those in the brain, reducing its blood supply and therefore its oxygen supply.
encyclopedia.com
Carbon dioxide (CO2) has a profound and reversible effect on cerebral blood flow, such that hypercapnia causes marked dilation of cerebral arteries and arterioles and increased blood flow, whereas hypocapnia causes constriction and decreased blood flow...Although several mechanisms involved in hypercapnic vasodilation have been proposed, the major mechanism appears to be related to a direct effect of extracellular H+ on vascular smooth muscle. This is supported by findings that neither bicarbonate ion nor changes in Pco2 alone affect cerebral artery diameter...
ncbi.nlm.nih.gov
