CO2 Reactivity of the Fast and Slow Clearing Compartments

• Regional cerebral blood flow measurements have been made at two levels of Paco, using the clearance of 133Xenon injected into the internal carotid artery. Specific and percent changes in blood flow per mm Hg change in Paco, (CO2 reactivity) have been calculated for the fast and slow clearing tissue (Ff and Fs) and F initial. Mean hemisphere CO2 reactivity was marginally greater in the fast clearing tissue than in the slow clearing tissue (P = 0.05). On a regional basis the greater CO2 reactivity of Ff over Fs was significant in five areas (P < 0.05). A strong positive linear correlation between mean specific reactivity and conductance (the reciprocal of resistance) has been demonstrated for Ff and Fs and confirmed in the F initial. Additional Key Words regional cerebral blood flow 133Xenon internal carotid artery • It is well known that cerebral blood flow (CBF) can be altered by changes in the arterial carbon dioxide tension (Paco,).1"4 Cerebrovascular resistance is increased by the vasoconstrictor effect of hypocapni