Autoregulation and Hyperemia of Cerebral Blood Flow as Evaluated by Thermal Diffusion

A thermal diffusion flow probe gave a quantitative dynamic recording of cerebral blood flow (CBF) during bleeding and transfusion in experimental animals. Autoregulation was readily demonstrated in nine of 12 animals and was found only with gradual hypotension. After autoregulation was lost, no increase in CBF could be obtained with carbon dioxide inhalation. Reactive hyperemia was demonstrated consistently following compromised CBF and, again, no increase in CBF with hypercarbia could be obtained until the hyperemia had subsided. Once hyperemia ceased, autoregulation could be demonstrated again in the same animal.