The Hydrogen Clearance Method in Assessment of Blood Flow in Cortex, White Matter and Deep Nuclei of Baboons

The technique of hydrogen clearance by an inhalation method is discussed. The electronic instrumentation necessary to secure stability and reproducibility from the recordings is described. Clearance rates in gray matter of about 80 ml/100 gm per minute in the cortex and putamen have been obtained, and of about 20 ml/100 gm per minute in white matter.Clearance curves have invariably been monoexponential in character in white matter, and in over half the cases in the putamen. In the remainder of the putamen curves and in 60% of the cortical clearance curves, the curves could be resolved into only two exponentials. Using bicompartmental analysis, the fast-clearing components of biexponential curves in both cortex and deep nuclei gave the same figures as clearance curves of an entirely monoexponential character from these two tissues. The importance of recirculation time, concentration of hydrogen inhalation, and verification of the tissue placement by subsequent dissection are discussed. The capacity of the method to detect sudden changes in flow during clearance is described.