Tracking cerebral blood flow regulation during incremental ascent to altitude: Effect of superimposed hypoxia and hypocapnia

High altitude exposure imposes a unique cerebrovascular challenge due to the presentation of two opposing blood gas stimuli. Specifically, hypoxia causes cerebral vasodilation, increasing cerebral blood flow (CBF), whereas respiratory-induced hypocapnia causes cerebral vasoconstriction, decreasing CBF. Accordingly, arterial blood gases are large determinants of resting CBF, but the conflicting nature of these two superimposed chemostimuli presents a challenge in tracking CBF responsiveness with ascent to altitude. The extent that conflicting arterial blood gas variables affect CBF during incremental ascent to moderate altitude (i.e., the typical ascent profile for trekkers) is unclear. In 16 lowlanders during incremental ascent to altitude, we aimed to (a) characterize the relationship between arterial blood gas stimuli with regional and global CBF and (b) develop a novel index to track changes in CBF in relation to simultaneous but conflicting chemostmuli. During ascent to 4370m over seven days in the Ne...