The measure in vivo of regional cerebral oxygen utilization by means of oxyhemoglobin labeled with radioactive oxygen-15

Abstract

Regional cerebral oxygen utilization rate is measured in vivo by the following method: A small volume of blood with radioactive oxygen-15-tagged hemoglobin is rapidly injected into the internal carotid artery of the patient under study. The first injection is followed by the injection carried out under identical circumstances but with blood labeled with water-¹⁵O. After each injection, the distribution of the radioactive label in the brain is measured and recorded, as a function of time, by six collimated scintillation probes placed over the subject's head. The recording, subsequent to the first injection, reflects (a) the arrival of the labeled oxygen into the tissues, (b) its partial conversion into water of metabolism, and (c) the washout of labeled water from the brain. The ratio of the amount of labeled water formed to the amount of oxygen perfusing the tissues, which can be derived from the recording, is a measure of fractional oxygen utilization. The second injection provides a measure of blood flow by the interpretation of the washout of labeled water from brain tissues. The product, fractional oxygen utilization × blood flow × arterial oxygen content, gives a measure of oxygen utilization rate. Some aspects of the validity of this method are tested by the injection of a nondiffusible indicator, carboxyhemoglobin-¹⁵O. Regional cerebral oxygen utilization rates for a series of patients with cerebral pathology are reported.