In 1945, Kety developed the first quantitative and reproducible method for measuring cerebral blood flow. The implications of that simple statement will escape those not old enough to recall the bizarrely unreliable techniques previously used. Before the new method was introduced, oxygen tension was measured twice in blood sampled from the internal carotid artery and the internal jugular vein; if blood flow was assumed to be constant during that interval, changes in the differential between arterial and venous oxygen levels reflected metabolism; if cerebral metabolism was taken as unchanged, the difference could only reflect changes in blood flow. But which of the two was the case? There was no way to know. Kety used nitrous oxide, an inert but soluble gas, to measure blood flow (by applying the Fick principle). Once blood flow had been calculated, changes in arteriovenous oxygen tension provided an index of metabolism.
Kety and his colleagues applied the method to healthy volunteers, and to patients with various ailments—essential hypertension, diabetic acidosis and coma, increased intracranial pressure and senile dementia. Major differences were evident in these patients. But blood flow and oxygen consumption in people with schizophrenia were entirely within the normal range. Kety knew that such findings did not rule out the possibility of biologically important changes in particular brain regions of schizophrenics. Thus, measuring differences in regional blood flow became his next objective.
This is a preview of subscription content, access via your institution