Positron emission tomographic evaluation of cerebral blood flow during state anxiety in simple phobia.

The present study was undertaken to clarify some of the conflicting findings of previous reports on the effect of state anxiety on cerebral blood flow (CBF). Seven subjects with simple phobia of small animals were studied to permit the generation of wide ranges of anxiety. Each subject received five positron emission tomography (PET) scans in a rest-fear-rest-fear-rest, repeated-measures paradigm. A population of eight normal controls was employed. The phobic stimuli produced significant increases in state anxiety during fear and significant differences in physiologic measurements between the fear and rest scans. Absolute global and regional CBF was significantly lower during fear scans than during rest scans; however, when hypocapnia resulting from anxiety-induced hyperventilation was taken into account, the pattern vanished, and all global and regional CBF differences among scans became not significant. Resting global and regional CBF values in the phobic subjects did not significantly differ from those of the normal controls. That a relationship between anxiety and CBF was not found in 35 scans among seven subjects strongly suggests that CBF changes induced by state anxiety are either not presently measurable by PET techniques or that such a relationship may not exist. These findings should also reduce concerns that subject anxiety may confound CBF measurements during routine PET scanning.