Age-related cerebrovascular response to global ischemia in pigs

We tested the hypothesis that 1- to 2-wk-old pigs (piglet) have improved recovery of cerebral blood flow (CBF), cerebral oxygen consumption (CMRO₂), and somatosensory-evoked potentials (SEP) compared with 6- to 8-mo-old pigs (pig) after transient global cerebral ischemia. All animals were anesthetized with pentobarbital sodium. After tracheostomy ventilation was adjusted to maintain normoxia (arterial oxygen pressure, 100-150 mmHg) and normocarbia (arterial carbon dioxide pressure, 35-40 mmHg). Arterial blood gases, blood pressure, and hemoglobin concentration remained within physiological limits throughout the experiment. Cerebral ischemia was produced by sequentially tightening ligatures around the inferior vena cava and ascending aorta. During ischemia the electroencephalogram and SEP became isoelectric within 40 and 120 s, respectively. At 10 min of reperfusion hyperemia occurred in most brain regions (e.g., whole brain: piglet, 270 ± 45%; pig, 316 ± 48%). In pigs delayed hypoperfusion occurred in all regions except white matter. In contrast, piglets only had delayed hyperperfusion to the brain stem and caudate nucleus. Throughout reperfusion CMRO₂ was decreased in pigs (3.3 ± 0.4 to 1.9 ± 0.2 ml·min^-1·100 g^-1) but was not different from control (2.7 ± 0.3 ml·min^-1·100 g^-1) in piglets. By the end of reperfusion SEP amplitude was closer to control in piglets than pigs (55 ± 9 vs. 32 ± 4% of control). We conclude that 1- to 2-wk-old piglets have quicker return of CBF, CMRO₂, and SEP to control values after global ischemia, which mechanistically may explain previous reports of improved neurological recovery in young animals after transient ischemia.