Carbon Dioxide Levels and Cerebral Blood Flow

To the Editor.—  We wish to point out that the article by Ariel et al entitled "Regional Cerebral Blood Flow in Schizophrenics" (Archives 1983;40:258-263) needs clarification on an important point. There is a general consensus that carbon dioxide is the single, most powerful determinant of cerebral blood flow (CBF).¹ Even mild changes in carbon dioxide levels are associated with profound CBF alterations.² The authors did not provide any information at all about this important variable. One might argue that the study was on resting CBF and that only acute changes in carbon dioxide affect CBF.³ However, carbon dioxide levels should have been monitored to make sure that no acute changes or rapid fluctuations took place during the measurement. Furthermore, the differential effects of acute and sustained carbon dioxide changes on CBF are unclear. It is difficult to interpret the results of this study without this crucial