Anxiety, pCO2 and cerebral blood flow

This study examined the effect of anxiety on cerebral blood flow at different levels of pCO(2) in healthy participants (N = 29). Three types of breathing were used to manipulate pCO(2) in a within-subject threat-of-shock paradigm: spontaneous breathing, CO2-inhalation and hyperventilation resulting in normo-, hyper- and hypocapnia. Transcranial Doppler ultrasonography was used to measure CBF velocity (CBFv) in the right middle cerebral artery, while breathing behavior and end-tidal pCO(2) were monitored. During normocapnia, elevated anxiety was clearly associated with increased CBFv. Consistent with the cerebral vasoconstrictive and vasodilating effects of, respectively, hypo- and hypercapnia, we observed a positive linear association between CBFv and pCO(2). The slope of this association became steeper with increasing anxiety, indicating that anxiety enhances the sensitivity of CBEv to changes in pCO(2). The findings may elucidate conflicting findings in the literature and are relevant for brain imaging relying on regional cerebral blood flow. (C) 2013 Elsevier B.V. All rights reserved.