Age-related cerebrovascular reactivity to CO₂ after cerebral ischemia in swine

We tested the hypothesis that cerebral blood flow (CBF) reactivity to CO₂ after global ischemia takes longer to recover in 1- to 2-wk-old piglets than in 6- to 10-mo-old pigs. All animals were sedated with ketamine and anesthetized with pentobarbital sodium. Cerebral ischemia was produced by sequentially tightening ligatures around the inferior vena cava and ascending aorta for 10 min. The microsphere-determined CBF response to hypercapnia (arterial PCO₂ ~65 mmHg) was depressed at 60 min of reperfusion (9 ± 6% of preischemia; means ± SE) and remained depressed at 120 min (33 ± 23% of preischemia, means ± SE) in young pigs. In older pigs, the response was also depressed at 60 min of reperfusion (21 ± 9% of preischemia) but was not depressed at 120 min. The pattern for recovery of hypercapnic reactivity was present in most brain regions except cerebellum, where CO₂ reactivity returned to control in young animals by 120 min of reperfusion. The response to hypocapnia (arterial PCO₂ ~25 mmHg) was also better preserved in older pigs. In older pigs recovery of CO₂ reactivity during reperfusion paralleled recovery of cerebral O₂ consumption over time. We conclude that older pigs have quicker return of CBF CO₂ reactivity following transient global ischemia, which may be due to age-related differences in mechanisms of vascular reactivity.