The Effects Of Two Repeated Posture Changes On Cardiovascular Regulation In Humans

Objective:To study the Effects of two repeated posture changes on cardiovascular regulation in humans,and the effects of repeated position changes on it were further elucidated and the mechanism was discussed,which provided the basis for the application of this method in the research and practice of Aeronautics and Astronautics.Methods:30 volunteers were randomly divided into two groups of A and B,each group were 15.Group A were exposed to HDT/HUT pattern of repeated body position change test and group B were to SUP/HUT.Each group underwent the same mode test two times,and the interval between two times was 7 days at least.Before and after the first time test,subjects were examined to the vertical position,and before and after the second times test,subjects were examined to the low position.Check the data of supine by last 30s and the data of head up(or head down)by the first 30s to the examine of head up and head down.Analysis the changes of heart rate(HR),stroke interval(IBI),stroke volume(SV),cardiac output(CO)and ejection time(EJT),blood pressure(SBP,DBP MAP),and total peripheral resistance(TPR);10ml blood in each position at 2min was took,and analysis the changes of hematocrit(HCT),plasma renin activity(PRA),vasopressin(AVP),angiotensin ?(A ?),antidiuretic hormone(ADH),aldosterone(ALD),atrial natriuretic peptide(ANP).Results:(1)Head-up tilt examination:After the test of HDT/HUT,supine position SV decreased significantly;Orthostatic position SBP,EJT and IBI decreased significantly,HR,HCT,ANP were increased significantly;After the test of SUP/HUT,DBP,MAP in supine position were increased significantly;Orthostatic position DBP increased significantly,SV and PRA were decreased significantly,MAP increased.(2)Head-down tilt examination:After HDT/HUT test,SBP,DBP,MAP and TPR were increased significantly in supine position and head down position,while PRA was decreased significantly;HCT increased significantly in supine position.After the SUP/HUT test,the level of DBP,MAP and TPR increased significantly in the supine position,and the PRA decreased significantly,and the PRA decreased significantly at the head-down position.Conclusion:(1)There are different influences on the orthostatic stress response of two patterns of repeated position change tests.HDT/HUT mode may not be conducive to orthostatic endurance maintenance,and SUP/HUT mode can improve orthostatic tolerance.The mechanism may be closely related to the changes in the hematocrit caused by repeated body position changes(the effective circulation volume of indirect reaction).(2)The effects of two repeated posture tests on human head down stress response are different,mainly due to the difference of blood pressure characteristics,which needs further research and validation.