Comparison between the Photoelectric Method and H2 Clearance Method for Measuring Cerebrocortical Blood Flow in Cats

The photoelectric method using carbon black as a nondiffusible tracer of blood was compared with the hydrogen clearance (H 2 ) method in nine anesthetized cats. A photoelectric apparatus and H 2 electrode were applied to a small region of the cerebral cortex (left ectosylvian gyrus) for simultaneous measurement of the regional CBF. The values of CBF(H 2 ) and CBF(photoelectric) were 50.7 ± 19.2 and 52.1 ± 14.5 ml − 100 g −1 · min −1 , respectively. CBF(H 2 ) and CBF(photoelectric) were found to correlate well ( r = 0.588, p < 0.01) when changes in CBF were induced by CO 2 inhalation, exsanguination, hyperventilation, and occlusion of the middle cerebral artery. The correlation between CBF(H2) and CBF(photoelectric) was much better in the case of intraindividual comparisons ( r = 0.957, p < 0.01). In addition to its merits in common with the H 2 clearance method, such as handiness, low cost, and strict regionality, the photoelectric method displayed the following advantages: time-to-time measurements of CBF (<20 s), immediate display of the microcirculatory flow pattern, and simultaneous monitoring of cerebral blood volume. However, measurements from deep structures of the brain are better performed by the H 2 method despite the disadvantage of the use of a potentially explosive gas.