USE OF DIFFUSION TENSOR IMAGING TO ASSESS THE IMPACT OF NORMOBARIC HYPEROXIA WITHIN NORMAL APPEARING BRAIN FOLLOWING TRAUMATIC BRAIN INJURY
Introduction We have shown that normobaric hyperoxia (NH) may rescue metabolically compromised tissue following traumatic brain injury (TBI).
Objective To assess the impact of NH within normal appearing brain using diffusion tensor imaging (DTI).
Materials and Methods Fourteen patients with severe TBI underwent DTI at baseline and following NH (80% oxygen). Twenty-six controls underwent DTI at baseline, while 7 controls underwent DTI at 21%, 60% and 100% oxygen. We used the 95% prediction interval (PI) for zero change to demonstrate regions showing a change following hyperoxia.
Results Baseline DTI showed regional variability, with differences in all DTI parameters compared with controls (p < 0.05). Following NH there was no DTI change in controls. In patients the apparent diffusion coefficient (ADC) was unchanged within deep grey and mixed cortical regions despite baseline values that were lower than control (p < 0.05). One white matter region showed a fall in fractional anisotropy (FA) and increase in radial diffusivity (p < 0.05). However, many other regions showed a non-significant trend for lower FA and axial diffusivity. Eighteen per cent of regions showed an FA decrease and 4% showed an increase greater than the 95% PI for zero change.
Conclusions NH does not normalise ADC values within non-lesion deep grey and mixed cortical regions, and may reduce FA in normal appearing white matter. The mechanistic basis for these findings is unclear, but imply that a short period of NH is not beneficial within normal appearing brain, and raise the concern that NH may worsen axonal injury.