Gray matter nulled and vascular space occupancy dependent fMRI response to visual stimulation during hypoxic hypoxia

Effects of reduced oxygen availability on the vascular response and oxygen consumption of the activated human visual cortex

“…Despite the availability of oxygen as of crucial importance in energy metabolism, few human studies have analyzed how the cerebral metabolic rate of oxygen and the vascular response are affected by mild hypoxia at rest and during increased neuronal activity, ie, during stimulation . The literature on the impact of reduced oxygen availability in in vivo human physiology utilized a degree of mild hypoxia that yielded arterial blood oxygen saturation in the range of 80–85% .…”

Feasibility of functional MRI at ultralow magnetic field via changes in cerebral blood volume

“…In CBV-based functional imaging the signal changes arise from the difference in T 1 between brain tissue, cerebrospinal fluid (CSF) and blood. The CBV response can be measured with the vascular space occupancy (VASO) method (Lu et al,2003), aimed at nulling the blood compartment selectively, or by the closely related scheme using gray matter nulling (GMN) (Wu et al, 2008;Shen et al, 2009;Shen et al, 2012). Our group has determined a T 1 -difference between CSF and blood of more than a factor of five, and between blood and brain tissue of more than a factor of two (Inglis et al,2013), making CBV-based sequences an attractive possibility for ULF-fMRI.…”

O acoplamento neurovascular e metabólico do córtex visual ativado de sujeitos jovens saudáveis durante a disponibilidade reduzida de oxigênio

“…Results from literature are controversial: the amplitude of CBF and CBV responses is not affected by hypoxia (6,11,(170)(171)(172), although BOLD amplitude has been reported to be not significantly affected (170,172) or decreased (6). Activated areas decrease in BOLD-fMRI during hypoxia as compared to normoxia is a consistent finding between studies (6,(170)(171)(172), although CBF and CBV areas changes were reported to remain unaltered (11,170) or decrease (6,(170)(171)(172)(173) during hypoxia. Finally, two recent studies calculated estimates of ΔCMRO 2 due to stimulation based on the calibrated BOLD technique, which revealed a reduction of ΔCMRO 2 during mild hypoxia as compared to normoxia (174,175).…”

“…reported no amplitude changes in the visual cortex (170), although a 77% area reduction was observed in the motor cortex (172). Unaltered CBV amplitude in response to mild hypoxia is a consensus between studies (6,171,173), Hence, there would be a lesser mismatch between CBF and CMRO 2 during mild hypoxia. However, previous studies that focused on analyzing the effects of mild hypoxia in the brain electrical activity showed both event-related brain potentials and reaction times altered during mild hypoxia as compared to normoxia (184)(185)(186)(187).…”

“…Mild hypoxic hypoxia regulated by an inspired gas mixture containing 12% O 2 has been safely applied in studies in the past decade, leading to arterial oxygen saturation levels of approximately 85% without any related historic of discomfort (11,(170)(171)(172). Few human brain studies have analyzed how physiological parameters related to the vascular response, such as BOLD, CBF, CBV and CMRO 2 are affected by mild hypoxia, both at baseline (i.e., in absence of external stimuli) and during increased neuronal activity (6,11,(170)(171)(172)(173).…”