GLOBAL CEREBRAL BLOOD-FLOW DECREASES DURING PAIN

Positron emission tomography studies have identified a common set of b rain regions activated by pain. No studies, however, have quantitative ly examined pain-induced CBF changes. To better characterize CBF durin g pain, 14 subjects received positron emission tomography scans during rest, during capsaicin-evoked pain (250 mu g, intradermal injection), and during innocuous vibration. Using the (H2O)-O-15 intravenous bolu s method with arterial blood sampling, global CBF changes were assesse d quantitatively. Painful stimulation produced a 22.8% decrease in glo bal CBF from resting levels (P < 0.0005). This decrease was not accoun ted for by arterial PCO2, or heart rate changes. Although the exact me chanism remains to be determined, this pain-induced global decrease re presents a previously unidentified response of CBF.