CEREBRAL BLOOD-FLOW AUTOREGULATION AFTER EXPERIMENTAL SUBARACHNOID HEMORRHAGE DURING HYPERVENTILATION IN RATS

The purpose of the current study was to investigate whether impaired cerebral blood flow (CBF) autoregulation after experimental subarachnoid hemorrhage (SAH) could be restored by hyperventilation. SAH was induced in rats by injection of autologous blood into the cisterna magna. CBF was measured using intracarotid injection of Xe-133. Autoregulation was studied in four groups of animals: normoventilated controls, hyperventilated controls, normoventilated animals with SAH, and hyperventilated SAH animals. PaCO2 in the normocapnic groups was 38-42 mm Hg and 25-30 mm Hg in the hypocapnic groups. CO2 reactivity after SAH was intact as hyperventilation decreased CBF by 38% in controls and by 46% in animals with SAH. Mean arterial pressure (MAP) was unaffected in both groups. In the controls, hypocapnia caused a shift of the autoregulation curve toward lower CBF levels without changing the lower limit of autoregulation. In the SAH group in the normocapnic state, autoregulation was absent as the obtained curve was a straight line, such that CBF increased with increasing MAP. However, during hypocapnia CBF was constant in the MAP interval between 60-150 mm Hg showing reestablishment of autoregulation by hyperventilation.