FIGURE 1

Mean percent change in middle cerebral artery (MCA) blood flow velocity during 33% ^SXe/67% O₂ inhalation, as determined by transcranial Doppler measurements at 30-second intervals in 10 young adult males (Obrist et al., 1992). Blood velocity gradually increased during the 4.5-minute ^SXe inhalation, reaching a peak value of 35% 13% (mean SD) above preinhalation baseline values. Concurrent CBF measurements by the intravenous ¹³³Xe method yielded a 28% 17% increase from baseline values. Arrows indicate the time of ¹³³Xe injection and start of clearance curve fitting (see Discussion). Note the rapid decline in blood velocity after terminating ^SXe inhalation.