Cerebral blood flow during experimental hypoxaemia and ischaemia in the newborn piglet

The effect of selective hypoxaemia or ischaemia on cerebral blood flow was studied in 14 newborn piglets with the microsphere method. Surgery and experiments were performed under general anesthesia with 70% nitrous oxide. The spontaneously breathing piglet was then exposed to either low (zero) oxygen in the inspired air (hypoxaemia), or a graded tourniquet (3-5 kg string weight) of the neck above the level of the tracheostomy (ischaemia). Cerebral blood flow was measured at baseline, during the hypoxaemic/ischaemic insult, and 30 and 60 min thereafter. Brainstem blood flow was remarkably stable during both ischaemia and hypoxaemia. The reduction in blood flow to the cerebrum and to the cerebellum was greater during ischaemia than during hypoxaemia. Reactive hyperaemia followed hypoxaemia but was not obvious after selective ischaemia. Ischaemia and hypoxaemia thus seem to have different effects on cerebral blood flow.