Anxiety, pCO2 and cerebral blood flow.

Abstract 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, CO 2 -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 CBFv 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.