Acute effects of cigarette smoking on global cerebral blood flow in overnight abstinent tobacco smokers.

We examined whether cerebral vascular reactivity to 5% CO2/95% O2 would be a useful, independent measure of effects of tobacco smoking on global cerebral blood flow (gCBF). The acute effects during smoking one's favorite brand of cigarettes were determined after overnight tobacco abstinence. Positron emission tomography was used to quantitatively measure gCBF using H(2)15O in 10 right-handed young-adult male volunteer tobacco smokers. After a 12-hr abstinence, gCBF measurements were repeated six times at 15-min intervals: First baseline, 5% CO2/95% O2 inhalation, first cigarette smoking, second baseline, 5% CO2/95% O2 inhalation, and second cigarette smoking. Surprisingly, no significant change was seen in mean gCBF during smoking compared with baseline. However, the increase in arterial plasma concentration of nicotine correlated inversely with gCBF. Out of 19 smoking sessions, gCBF increased in 7, decreased in 7, and was unchanged in 5 sessions. The gCBF increased during smoking when baseline gCBF was relatively low, whereas gCBF decreased when baseline gCBF was relatively high. Both vascular reactivity and estimated gCBF plus arterial nicotine concentrations were useful measures to predict the changes in measured gCBF. These individual differences result in important bimodal effects of smoking on the brains of different young adult tobacco smokers.