Normal Average Value of Cerebral Blood Flow in Younger Adults is 50 ml/100 g/min

Many studies of CBF in normal humans have been reported in the literature over the last 40 years, using a variety of techniques yielding widely varying average values for resting CBF in normal younger adults-from �35 to �75 mlll00 g/min, They cannot all be correct, because there is no reason to doubt that resting normoxic and normo­ capnic adults having a normal hematocrit must also have practically the same average CBF indepen­ dently of sex, race, country, climate, etc, Normal adults show a very slight decrease of CBF with age, which is on the order of 0,5%/year (Naritomi et aI., 1979; Davis et aI., 1981; Hagstadius and Risberg, 1983; Matsuda et ai" 1984), The proposition to be presented here is that normal adults of mean age 30-40 years have an average CBF of 50 ml/l00 g/min and that the error of this estimate, as will become apparent from the following discussion, is unlikely to exceed 5 ml to either side, Thus the thesis proposed is-any de­ viation of mean CBF outside this range of 45-55 mll100 g/min must be due to systematical errors of the method used, One cannot, for obvious reasons, conclude the converse, viz" that a mean normal value inside the range mentioned means that no systematical errors influence the method used, Clearly, the sum of er­ rors may so balance each other as to yield the "cor­ rect" mean value yet with the errors not necessarily canceling out in other states, so that despite correct mean normal values, the method is nevertheless not valid at all-or not quite valid-depending on con­ ditions. The first study to be discussed is the classical report of Kety and Schmidt from 1948. It gave the first detailed description of the nitrous oxide method, and great care was exerted with all details. The mean CBF in 3 2 studies of 13 young male adults, college students �20 years of age, was 56 mlll00 g/min in normocapnia. Owing to the cessa­ tion of the study at 10 min, this method cannot fully take into account the white matter flow, an error that is slightly enhanced because the arterial curve is not completely horizontal. The combined effect