Effect of hyperventilation on organ tissue blood flow in brain and ventricles of rabbits measured by the colored microsphere method

We investigated the changes in regional cerebral blood flow and myocardial blood flow during hyperventilation. Japanese white rabbits were anesthetized with a mixture of 50% oxygen and 50% nitrous oxide with 1.0% sevoflurane. Hyperventilation (with hypocapnia) was induced by adjusting the ventilation to achieve a PaCO_2 of 25〜30mmHg. Following hypocapnia, normocapnia was attained by loading CO_2 gas without changing the conditions of ventilation to increase PaCO_2 to 40〜45mmHg. Blood flow in the cerebral cortex, cerebellum, thalamus, pons, hippocampus, right ventricle, and left ventricle were measured using the colored microsphere method in each rabbit during hypocapnia and 30 minutes after establishing normocapnia. The findings during hypocapnia and normocapnia were compared. Blood flow in the cerebral cortex and the cerebellum during hypocapnia was lower than during normocapnia, while myocardial blood flow was not affected by PaCO_2. These findings suggest that changes in blood flow in the cerebral cortex and cerebellum contribute to a large extent to the decrease in cerebral blood flow leading to loss of consciousness in patients with hyperventilation syndrome.