Changes in Cerebral Blood Flow and Arterio-Venous Oxygen Difference During Insulin Hypoglycemia. ∗

Previous work has disclosed that the arterio-venous oxygen difference of cerebral blood is diminished during insulin hypogly-cemia. 1 , 2 However, the arterio-venous oxygen difference is determined not only by the metabolic rate of the brain, but also by velocity of blood flow. Therefore, thd possibility exists that the smaller oxygen difference found may be due to a more rapid blood flow during hypoglycemia. Observations by Loman and Myerson 3 on human subjects and Leibel and Hall 4 on rabbits, have failed to demonstrate any marked changes in the rate of cerebral blood flow during insulin hypoglycemia uncomplicated by convulsions. However, for conclusive information regarding changes of brain metabolism, it is necessary to determine, simultaneously, the cerebral blood flow and the arterio-venous oxygen difference. The results of such a study on patients with schizophrenia are presented in this preliminary report.

Methods for the collection and analysis of the blood samples have been previously described. 2 The rate of blood flow in the internal jugular vein was estimated by a modification of the Gibbs thermostromuhr. This instrument proved to be at least as sensitive as the original and will be described elsewhere. Observations on the blood flow were made over long periods during which the position of the thermostromuhr in the vein was maintained constant. A special technique was devised which prevented error resulting from the formation of clots on the needle.

In 5 cases the blood flow and the arterio-venous differences were determined before injection of insulin as well as throughout the course of the coma and the subsequent administration of glucose. In 3 other instances the observations were begun during coma and continued until after arousal with intravenous glucose.