Cerebral vasoconstriction effects oxygen

There is some controversy concerning the cerebral vasoconstrictive effects of oxygen. Lambertsen et al. (L2) believe that the vasoconstrictive effect is due to the decreased Paooi brought about by hyperventilation (vide supra), rather than by a direct vasoconstrictive effect of oxygen. Jacobson et al. (J2) found that, under constant CO2 tensions, oxygen exerts a direct cerebral vasoconstrictive effect. 

Transgenic mice overexpressing EC-SOD have better neurological outcome and cognitive performance after severe cranial impact [171]. Such animals were, however, more susceptible to hyperbaric oxygen than control animals, an effect ascribed to sparing excessive levels of nitric oxide and thus blocking the normal vasoconstrictive response of the cerebral vasculature to hyperoxia [ 172]. 

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