Ultrasonic Evaluation Of The Effect Of High Altitude Hypoxia On Cerebral Blood Flow Regulation

Objectives1.Transcranial color-coded duplex Doppler（TCCD）technology was used to detect cerebral blood flow parameters under different hypoxia periods,to evaluate the regulation of cerebral blood flow during acute altitude and long-term altitude hypoxia exposure,and to evaluate the reserve capacity of cerebral blood vessels during hypoxia adaptation.2.TCCD was used to monitor the change of cerebral hemodynamics during intermittent progressive hypoxia preconditioning,evaluate the change trend of cerebral blood flow regulation at different acclimation heights,and provide effective indicators for the adaptation effect of altitude preconditioning.Methods1.A total of 137 subjects were enrolled in this study,which were divided into the following three groups:（1）Plain area group:64 residents in long-term plain area;（2）Acute altitude group:All subjects in the plain group received simulated acute altitude hypoxia exposure for 30 min;（3）Plateau group:73 long-term plateau residents were included.Heart rate and pulse oxygen saturation（Sp O₂）of subjects in the above three groups were recorded,and TCCD technology was used to observe the changes of blood flow parameters such as systolic peak velocity（Vs）,end of diastolic velocity（Vd）and mean blood flow velocity（Vm）,resistance index（RI）and pulsatile index（PI）of middle cerebral artery（MCA）of the three groups.Combined with breath holding test,the cerebral vascular reactivity（CVR）of of different hypoxia time was evaluated by breath-holding index（BHI）.In addition,acute altitude subjects were divided into two age groups（≤30years old and>30 years old）to compare the difference of CVR changes after hypoxia.2.Ten healthy volunteers were included as research subjects,and underwent intermittent and progressive simulated hypoxic exposure training for 4d in a normally hypoxic chamber,once per day,120min per time,rising one height per day（3900m to4500m）.Divided into the following groups according to height:（1）Basic value:cerebral blood flow parameters of all subjects before hypoxic preconditioning;（2）Group 1:all subjects were subjected to the cerebral blood flow parameters in the simulated altitude of3900m（oxygen concentration 12.39%）normally hypoxic chamber;（3）Group 2,all subjects were subjected to the cerebral blood flow parameters in the simulated hypoxia chamber at a height of 4100m（oxygen concentration 12.03%）;（4）Group 3:all subjects were given cerebral blood flow parameters in a simulated chamber with normal hypoxia at a height of 4300m（oxygen concentration 11.45%）;（5）Group 4,all subjects were subjected to cerebral blood flow parameters in a simulated chamber with a height of 4500m（oxygen concentration 11.34%）.TCCD was used to measure the changes of blood flow parameters of MCA during intermittent progressive hypoxia pretraining（simulated altitude 3900m,4100m,4300m,and 4500m）,including Vs,Vd,Vm,RI and PI.Combined with breath-holding test,BHI was used to assess changes in CVR at different altitudes.Meanwhile,heart rate and Sp O₂of all subjects were recorded.Results1.（1）Compared with plain group,Sp O₂of acute plateau group decreased,and heart rate increased（all P<0.01）,middle cerebral artery blood flow velocity（Vs,Vd,Vm）significantly increased（all P<0.01）,RI and PI had no statistical significance（all P>0.05）.In the altitude group,Sp O₂decreased,heart rate increased（all P<0.01）,Vd increased（P=0.005）,Vs,Vm differences were not statistically significant,RI and PI decreased（all P<0.01）.（2）Compared with acute plateau group,Sp O₂increased and heart rate increased（all P<0.01）,Vs and Vm decreased（P<0.01,P<0.05）,Vd showed no significant difference（P>0.05）,RI and PI decreased（all P<0.01）in plateau group.（3）After breath holding,the blood flow velocity（Vs,Vd,Vm）of middle cerebral artery increased significantly（all P<0.01）,while PI and RI decreased significantly（all P<0.01）.（4）BHI of acute plateau group was lower than that of plain group（P<0.01）;BHI in plateau group was lower than that in plain group（P=0.045）,but higher than that in acute plateau group（P=0.007）.（5）In the acute altitude group,the BHI change rate of>30 years old subjects was lower than that of≤30 years old subjects（P<0.05）.2.（1）The difference of Sp O₂among all groups was statistically significant（P<0.01）.After pairwise comparison,the Sp O₂of groups 1,2,3 and 4 was lower than the base value,and the difference was statistically significant（all P<0.05）.（2）There was no significant difference in heart rate among all groups（P>0.05）.（3）There were statistically significant differences in middle cerebral artery flow velocity（Vs,Vm and Vd）among all groups（all P<0.05）.Pairwise comparison after test showed that cerebral blood flow velocity（Vs,Vm and Vd）in the first group was higher than the basic value,and the difference was statistically significant（all P<0.05）.（4）The difference of PI among all groups was statistically significant（P=0.024）.After pairwise comparison,the PI of the first group was lower than the basic value,and the difference was statistically significan（P<0.05）.There was no statistical significance in RI among all groups（P>0.05）.（5）There was no significant difference in BHI among groups（P=0.335）.（6）Spearman rank correlation analysis showed that Vs was negatively correlated with Sp O₂（r=-0.373,P=0.008）.The other parameters had no correlation with Sp O₂（P>0.05）.Conclusions1.The application of TCCD technology can detect the cerebral hemodynamic parameters in real time and accurately,providing objective basis and research basis for the evaluation of cerebral blood perfusion and cerebrovascular reserve capacity during acute or long-term altitude operation.2.Using TCCD to monitor the changes of cerebral blood flow during intermittent progressive hypoxia preconditioning can objectively and effectively evaluate the adaptation effect of hypoxia preconditioning,and also provide theoretical basis for the prevention of hypoxia at high altitude.