Reduced cerebral blood flow but intact reactivity to hypercarbia and hypoxia following subarachnoid hemorrhage in rabbits

Subarachnoid hemorrhage (SAH) was produced in rabbits by four subarachnoid injections of blood (n = 7) or saline (n = 6); a control group (n = 6) had no injections. Basilar artery vasospasm was assessed by serial angiograms. Resting CBF (microspheres) and CBF reactivity to hypercapnia (65 and 85 mm Hg) and hypoxia (fractions of inspired oxygen of 0.15 and 0.10) were determined. Basilar artery vasospasm was seen with SAH. Resting CBF was reduced by 31% (SAH 43 ± 12, saline 65 ± 17, control 60 ± 21 ml 100 g^-1 min^-1), and resting cerebrovascular resistance was increased (SAH 1.84 ± 0.30, saline 1.31 ± 0.49, control 1.39 ± 0.25 mm Hg ml^-1 100 g^-1 min^-1) after SAH. CBF rose to a similar degree in all three groups in response to hypercarbia and hypoxia. We conclude that resting CBF is reduced in this model of SAH, but vascular reactivity remains intact.