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

The purpose of the current study was to investigate whether impaired c erebral blood flow (CBF) autoregulation after experimental subarachnoi d hemorrhage (SAH) could be restored by hyperventilation. SAH was indu ced in rats by injection of autologous blood into the cisterna magna. CBF was measured using intracarotid injection of Xe-133. Autoregulatio n was studied in four groups of animals: normoventilated controls, hyp erventilated controls, normoventilated animals with SAH, and hypervent ilated SAH animals. PaCO2 in the normocapnic groups was 38-42 mm Hg an d 25-30 mm Hg in the hypocapnic groups. CO2 reactivity after SAH was i ntact as hyperventilation decreased CBF by 38% in controls and by 46% in animals with SAH. Mean arterial pressure (MAP) was unaffected in bo th groups. In the controls, hypocapnia caused a shift of the autoregul ation curve toward lower CBF levels without changing the lower limit o f autoregulation. In the SAH group in the normocapnic state, autoregul ation 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 reestablishm ent of autoregulation by hyperventilation.