CBF And Visual Task Induced Neuronal Activity After Hypoxia/Reoxygenation:MRI Studies

ObjectivesThe brain consumes 20%of oxygen,which takes the most oxygen consumption of body to maintain normal brain function,the brain can be easily suffer from hypoxia.Therefore,A series of responses in hypoxia,such as headache and dizziness.Previously,we have studied the CBF and brain structures in mountain climbers,soldiers and volunteer teachers,and found that the changes of brain functions after hypoxia are mainly reflected in the decline of visual spatial cognitive construction ability.Therefore,in-depth studies on the brain mechanism from CBF and visual task induced neuronal activity after hypoxia/reoxygenation.Materials and methodsThis study recruited 23 Xiamen University undergraduates who went to Lhasa Damxung County(altitude 4300m)as volunteer teachers in August 2017,including 11 females and 12 males,with an average age of 19.4±0.9.Tested before(Test 1),back to Xiamen within one week(Test 2)and back to Xiamen after three months(Test 3),the physiological tests(hematological measure,blood pressure,,heart rate,pulse,oxygen saturation and lung function),behavior tests(acute mountain sickness,De-acclimatization symptoms,anxiety and depression),TCD and brain MRI.MRI data include 3D T1,ASL,and resting and task-activated fMRI.In addition,we recruited 13 low-altitude controls with matched age,gender,and educational background to verify whether the learning effect affects the behavior test results at the same time interval.All tests were analyzed by intergroup paired t test.ResultsTest 2 and Test 1 were paired with T test,FEV1(P=0.03 9),FEV1/FVC(P=0.020),the number of red blood cells(P=0.003)and hemoglobin(P<0.001)were significant increased.The results of TCD showed that the Vs and Vm of the BA were significant reduced.The results of ASL showed that the CBF of the left central posterior gyrus,cingulate gyrus and superior frontal gyrus were significant increased;the CBF of the left precuneus,putamen,thalamus,cerebellar vermis,right temporal lobe and cerebellar vermis were significant reduced.The fMRI results in the clock task showed activation in the left inferior frontal gyrus,insula,medial frontal gyrus and right frontal gyrus,but inhibition of the right lingual gyrus.Furthermore,based on the resting state fMRI data,the whole brain functional connectivity analysis was performed with the visual cortex differential brain regions bilateral lingual gyrus as the seed.The connectivity of the left lingual gyrus with the left paracentral lobule,the right inferior parietal lobes and fusiform is enhanced,but the connectivity with the right angular gyrus is weakened;the connectivity of the right lingual gyrus with the inferior parietal lobes,the right fusiform gyrus,the right frontal gyrus and the right insular lobes is enhanced,but the connectivity with the right superior frontal gyrus is weakened.Test 3 and Test 1 were paired with T test.There was no significant difference in cardiopulmonary function and hematological measurement,but significant increase in systolic(P<0.001)and diastolic blood pressure(P=0.010).There was no significant difference in Vs and Vm of BA.The results of ASL showed that the CBF of the left middle temporal gyrus,lingual gyrus,cerebellum,parietal lobe,the temporal lobe,cingulate gyrus,the right amygdala,hippocampus,fusiform gyrus and cerebellum were significant reduced.The fMRI results in the clock task showed activation in the left lentiform nucleus,pyramis,posterior cingulate,superior temporal gyrus and middle temporal gyrus.Furthermore,based on the resting state fMRI data,the whole brain fcunctional connectivity analysis was performed with the visual cortex differential brain region bilateral lingual gyrus as the seed.The results of fMRI showed that the connectivity of the left lingual gyrus with the right fusiform gyrus,the anterior cingulate and left inferior semi-lunar lobule were enhanced,but the connectivity with the superior temporal gyrus was weakened;the connectivity of the right lingual gyrus with the right posterior cingulate gyrus,superior temporal gyrus,right insular lobe and the left tuber is enhanced.Conclusions(1)CBF was redistributed in different brain regions and blood flow supplied by BA in the posterior regions was significantly decreased after hypoxia;(2)Cells activity was inhibited in the visual cortex by spatial tasks;(3)Functional connectivity to visual cortex was enhanced;(4)Changes in cerebral blood flow and brain function caused by the hypoxia is reversible to the original level after a time when the normal oxygen level is restored.(5)Our study suggests that decreased CBF and inhibition of neuronal activity may be mechanisms of visual dysfunction after hypoxia.