Impact of hypobaric hypoxia on blood flow distribution in frontal lobes

Aim: Acute hypobaric hypoxia is well known to alter brain circulation and to cause neuropsychological impairment. However, very few studies have examined the regional changes occurring in the brain during acute exposure to extreme hypoxic conditions.
Methods: Regional cerebral blood flow response to hypoxia was investigated in six healthy subjects exposed to either normobaric normoxia or hypobaric hypoxia with ambient pressure/inspired oxygen pressure of 101/21 kPa and 50/11 kPa, respectively. After 40 minutes at the desired pressure they were injected 99mTc-HMPAO and subsequently underwent Single Photon Emission Computed Tomography. Regional Cerebral Blood Flow distribution changes in the whole brain were assessed by Statistical Parametric Mapping, a well established voxel-based analysis method.
Results: Hypobaric hypoxia increased regional cerebral blood flow distribution in sensorymotor and prefrontal cortices and in central structures. PaCO2 correlated positively and SatO2 negatively with regional cerebral blood flow in several temporal, parahippocampal, parietal and central structures.
Conclusions: These findings underscore the specific sensitivity of the frontal lobe to acute hypobaric hypoxia and of limbic and central structures to blood gas changes emphasising the involvement of these brain areas in acute hypoxia.