Dynamic Study Of CBF During Acute Hypoxia/Reoxygenation

ObjectivesBrain is the most important central nervous organ of human body,and its normal function is very important for life activities.The function of the brain mainly depends on aerobic metabolism.It is very sensitive to the oxygen environment changing,and even brain damage will occur in severe cases.However,there were hypoxia phenomena in altitude exposure and some clinical diseases.The changes in the brain during hypoxia have been fully studied,but the changes in the brain after repxygenation and whether there are sequelae are still unclear.Over the years,our laboratory has found that the insular and occipital lobes are significantly affected by hypoxia and reoxygenation through long-term studies of the army stationed in Tibet,the high altitude(HA)volunteer teaching team and the HA mountaineering team.This study focuses on observing the dynamic changes of Cerebral blood flow(CBF)during acute hypoxia/reoxugenation,especially in the insular and occipital lobes.To explore the relationship between CBF and cerebral oxygen metabolism,and further discussing the mechanism of CBF regulation to provide theoretical basis for the study of regional brain microenvironment and the treatment of diseases with hypoxia.Materials and methodsIn this project,19 undergraduate students from Xiamen University were recruited in October 2018.The subjects were all male,with an average age of 20±0.7 years.They were subjected to 30 min of hypoxia at 10%oxygen concentration.In normoxia before hypoxia,10 min and 30 min during hypoxia,and 1 h and 6 h during reoxygenation after hypoxia,all subjects underwent the following tests:1)Physiological measurements,including oxygen saturation(SpO2),respiratory rate,pulse and blood pressure;2)Behaviroral tests,including acute mountain sickness,depressive symptoms;3)Brain magnetic resonance imaging(MRI)scan,including 3D T1,arterial spin labling(ASL),and quantitative susceptibility mapping(QSM).Paired T test was used to compare the CBF result of hypoxia and reoxygenation with those of normoxia,and voxel-based morphometry(VBM)was used to analyze the significant difference clusters of the whole brain.Separately separate the difference clusters into regions of interest(ROI)and apply them to all subjects for extraction value analysis and dynamic analysis.The correlation between CBF and physiological measurements was also analyzed.ResultsCompared with the physiological measurements in normoxia,SpO2 at 10 min and 30 min of hypoxia significantly decreased,then the pulse,blood pressure and respiratory rate did not change significantly.The physiological measurements in reoxygenation were compared with those in normoxia,the respiratory rate increased significantly at 1h of reoxygenation,and there were no significant differences in other measurements.After 6 h of rexygenation,SpO2 increased significantly,and systolic blood pressure decreased significantly,others did not differ significantly.The results of CBF shows that after 10 min of hypoxia,the CBF first decreased,with a large but scattered brain regions,including the right cingulate gyrus,right middle frontal gyrus,right insula,left lentiform nucleus,left paracentral lobule,left occipital lobe and left middle frontal gyrus.When the hypoxia continued for 30 min,the reduced range of CBF beban to shrink and was concentrated temporal lobe,parietal lobe,prefrontal lobe and mainly in the cingulate gyrus.Meanwhile,there were the regions with increased CBF in left insula and left occipital lobe.After 1 h of reoxygenation,the regions of CBF decreased from a cluster in the cingulate gurus to scattered clusters near the cingulate gyrus.The increased area of also changed from left insula and left occipital lobe to right occipital lobe.After 6 h of reoxygenation,the CBF reduction regions were further reduced,but the cingulate gyrus was still the main cluster.The regions with CBF increased expanded around the left and right occipital lobes.The correlation analysis between physiological measurements and the CBF value of ROI in insula,occipital lobe and cingulate gyrus showed that there was a negative correlation between pulse and CBF in the right occipital at normoxia.In cingulate gyrus,there was a negative correlation between CBF and SpO2 at 10 min of hypoxia,and a positive correlation between CBF and SpO2 at 1 h of reoxygenation.At 6 h of reoxygenation,CBF in the right occipital lobe was negatively correlated with pulse.The analysis of ROI showed that the variation trend of CBF is opposite to the variation trend of magnetic susceptibility in left and right insula,left and right occipital lobe and cingulate gyrus.When CBF increased the susceptibility was decrease.However,CBF and susceptibility of the cingulate gyrus decreased synchronously at 30 min of hypoxia,indicating that cerebral metabolic activity may be decreased in this region.Similarly,the CBF and susceptibility of the right occipital lobe increased simultaneously at 30 min of hypoxia,indicating that cerebral metabolic activity may be increased in this region.Conclusions(1)During the acute hypoxia/reoxygenation,the changes of CBF showed the tendency of dispersion and aggregation.Morover,compared with hypoxia,CBF does not recover linearly.(2)During hypoxia/reoxygenation,the oxygen-sentive brain regions with changes in insular and occipital lobe first experienced changes in CBF.(3)There were differences in the distribution of CBF by acute hypoxia/reoxygenation in different brain regions,which were caused by cerebral oxyen metabolism.(4)The decreased cerebral oxygen metabolism,induced by hypoxia,in cingulate gyrus was to meet the increased cerebral oxygen metabolism in occipital lobe to maintain the homesasis of the brain.(5)During acute hypoxia/reoxygenation,CBF and brain metabolism were not simply coupled or uncoupled,but stable and adjustable.