Effects of reduced oxygen availability on the vascular response and oxygen consumption of the activated human visual cortex.
To identify the impact of reduced oxygen availability on the evoked vascular response upon visual stimulation in the healthy human brain by magnetic resonance imaging (MRI).



Functional MRI techniques based on arterial spin labeling (ASL), blood oxygenation level-dependent (BOLD), and vascular space occupancy (VASO)-dependent contrasts were utilized to quantify the BOLD signal, cerebral blood flow (CBF), and volume (CBV) from nine subjects at 3T (7M/2F, 27.3 ± 3.6 years old) during normoxia and mild hypoxia. Changes in visual stimulus-induced oxygen consumption rates were also estimated with mathematical modeling.



Significant reductions in the extension of activated areas during mild hypoxia were observed in all three imaging contrasts: by 42.7 ± 25.2% for BOLD (n = 9, P = 0.002), 33.1 ± 24.0% for ASL (n = 9, P = 0.01), and 31.9 ± 15.6% for VASO images (n = 7, P = 0.02). Activated areas during mild hypoxia showed responses with similar amplitude for CBF (58.4 ± 18.7% hypoxia vs. 61.7 ± 16.1% normoxia, P = 0.61) and CBV (33.5 ± 17.5% vs. 25.2 ± 13.0%, P = 0.27), but not for BOLD (2.5 ± 0.8% vs. 4.1 ± 0.6%, P = 0.009). The estimated stimulus-induced increases of oxygen consumption were smaller during mild hypoxia as compared to normoxia (3.1 ± 5.0% vs. 15.5 ± 15.1%, P = 0.04).



Our results demonstrate an altered vascular and metabolic response during mild hypoxia upon visual stimulation.



2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:142-149.
Department of Physics, University of Sao Paulo, Ribeirao Preto, Brazil.
Felipe
F
Rodrigues Barreto
Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.
Silvia
S
Mangia
Department of Physics, University of Sao Paulo, Ribeirao Preto, Brazil.
Carlos Ernesto
CE
Garrido Salmon
D000328:Adult; D001682:Biological Availability; D001783:Blood Flow Velocity; D002560:Cerebrovascular Circulation; D005074:Evoked Potentials, Visual; D005260:Female; D006801:Humans; D002534:Hypoxia, Brain / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014793:Visual Cortex / Q000503:physiopathology*; D014796:Visual Perception
D010100:Oxygen
CMRO2; functional MRI; mild hypoxia; neurovascular coupling; vascular response