The Measurement of Cerebral Blood Flow by External Isotope Counting*

Abstract

The Kety-Schmidt nitrous oxide method (2) is presently the only well-accepted technique for the quantitative estimation of human cerebral perfusion. In spite of theoretical objections (3) and practical limitations it has provided a wealth of otherwise unobtainable information. The procedure is tedious, however, and has remained predominantly a laboratory research tool.Efforts have continued to find an accurate, more adaptable method, but with limited success. Sapirstein and Hanusek (4-6) have reported measurements of regional blood flow in laboratory animals by use of K42, Rb86, and 4-iodo831 antipyrine, and Sapirstein has reported observations concerning the applicability of these materials to measurement of human cerebral perfusion (7,8). This investigation was designed to evaluate, clarify, and extend those observations by employing 4-iodo'8lantipyrine and Rb86Cl in the quantitative estimations of human cerebral blood flow. The effects of altered arterial pCO2 upon cerebral hemodynamics were evaluated by use of this research method. THEORETICAL CONSIDERATIONSRegional blood flow by indicator distribution. After a rapid intravenous injection of an indicator substance, mixing occurs during passage through the central circulation. The initial distribution throughout the body is directly proportional to the regional distribution of the cardiac output. The problem inherent in this method of determining organ blood flow is that of quantifying the *