Regional Cerebral Blood Flow in the Rat Measured by the Tissue Sampling Technique; a Critical Evaluation Using Four Indicators C14‐Antipyrine, C14‐Ethanol H3‐Water and Xenon133

Abstract The validity of the assumptions inherent in the tissue sampling technique for measuring cerebral blood flow was tested in the rat, using the 4 indicators C 14 ‐antipyrine, C 14 ‐ethanol, H 3 ‐water and Xenon 133 . Each one of the indicators was infused i.v. during either 30, 60 or 120 s and the blood flow was calculated from the integrated arterial curve and from the tracer concentration in the tissue. The calculated flows varied with the time of infusion, and at high perfusion rates all tracers gave flow values that were lower than those obtained with the Kety and Schmidt technique. For C 14 ‐antipyrine, the method gives an error already at normal perfusion rates. It is concluded that the cerebral uptake of the tracers is diffusion‐limited, and that the tissue sampling technique cannot be used for quantitative measurement of cerebral blood flow in high flow situations. However, the error of the method is considerably reduced if C 14 ‐ethanol is used and if the time of infusion is limited to 30 s.