A long term observation of local cerebral blood flow using the hydrogen gas clearance technique

Local blood flow was estimated in the cerebral hemispheres of conscious goats using implanted platinum electrodes and the hydrogen gas clearance technique over periods of several weeks. During the first days of the experiments the blood flow rate was either below 27 ml/100 g/min. or above 40 ml/100 g/min. A gradual decrease in flow was observed over five weeks. The final flow values were between 20 ml/100 g/min. and 30 ml/100 g/min. Carotid injections of serotonin, noradrenalin, or metaoxamine, and inhalation of 5% carbon dioxide produced only insignificant changes in local blood flow. The cause of the slow decrease of flow and the change from a biexponential to a monoexponential curve may be explained by local tissue changes during the observation periods.