Coupling between CBF and CMRO2 during neuronal activity

The central idea of the oxygen limitation model is that the oxygen extraction fraction E must decrease during neuronal activation, so a large change in cerebral blood flow (CBF) is required to support a small change in the cerebral metabolic rate Of O-2 (CMRO2). The model is expanded here to show that maintaining mitochondrial pO(2) at a constant non-zero level during activation, so that O-2 availability does not become limiting for CMRO2, still requires the fractional CBF change to be several times larger than the CMRO2 change. Furthermore, the expanded model also allows for a brief initial increase in E at stimulus onset with a corresponding transient dip in cytoplasm and mitochondrial pO(2). However, because the tissue pO(2) must increase to support a higher CMRO2, the tissue O-2 content itself would be an ambiguous signal for regulating CBF. For this reason, although the function served by a large CBF increase may be to support CNTRO2, the tissue O-2 content itself is probably not the key factor for regulation of CBF. (C) 2002 Elsevier Science B.V All rights reserved.