Comparative Study On The Influences Of Different Pattern Of Repeated Body Position Change Test On Cardiovascular Function

Objective:Subjects of the same group were exposed to two different patterns of repeated body position change tests. The purpose of this study was:to investigate cardiovascular effects of repeated body position change between HDT/HUT and SUP/HUT; to find out which stimulus pattern provides the largest physiological effects and, hence, presumably the largest countermeasure potential.Methods:There were12healthy subjects who were exposed to two different patterns of repeated body position change tests (HDT/HUT and SUP/HUT). Before and after the repeated body position change test, subjects were subjected to5min of+75°head-up tilt (HUT1and HUT2, respectively) from a horizontal position. The experimental protocols are as follo we: HDT/HUT:0°,5min—-15°,1.5min—+50°,1min—-15°,1.5min—+50°,1min—-15°,1.5min—+50°,1min—-30°,2min-+50°,1min—-30°,2min—+50°, lmin—-30°,2min—+50°,1min—-45°,3min—+50°,1min—-45°,3min—+50°,1min—-30°,2min—+50°,1min—-15°,1.5min-+50°,1min—0°,5min. SUP/HUT: Ten bouts of SUPINE-HUT were alternated. Each bout involved a2-min supine period followed by a1-min+75°HUT. The parameter at supine position was made as control. Heart rate (HR), BP (SBP, DBP, MBP), total peripheral resistance (TPR), stroke volume (SV), and cardiac output (CO) were determined during the whole test. We collected the cardiovascular parameters at20s and60s during every position to analyze.Results:1) In the HDT/HUT condition, at the first minute of+75°HUT2, DBP, MBP and CO were significantly decreased. Cardiovascular response index (CRI) was significantly elevated compared with HUT1. In the SUP/HUT condition, during the supine phase of HUT2, HR, CO were decreased compared with HUT1. SV and TPR were not changed. There were no differences in the tilt period for SBP, DBP and MBP compared with HUT1. CRI was no change compared with HUT1.2) The change of cardiovascular index was obvious and regular for both HDT/HUT and SUP/HUT. 3) Except for the first two position change, the change value in BP (△BP) for the pattern of HDT/HUT was less than the pattern of SUP/HUT. Except for the eighth position change, in each position of the20s, the change value in SV (△S V) and CO (△CO) for the pattern of HDT/HUT was less than the pattern of SUP/HUT.4) There was no change in the response of HR for tilt10compared with tiltl for both HDT/HUT and SUP/HUT. The trend of SV was similar with CO. In the HDT/HUT condition, SBP (p<0.05),MBP decreased for the last-15?0s and+50?0s compared with the first-15?0s and+50?0s. SBP decreased, DBP and MBP increased for the last+50?0s compared with the first+50?0s. However, these were not significant. TPR was larger than the first position change, but had no significant. In the SUP/HUT condition, DBP, MBP was significantly elevated for both supine and75(?)UT compared with the first tilt. SBP was significantly elevated for the last0?0s and+75?0s. TPR was significantly larger than the first position change.Conclusion:1) The cardiovascular responses of two patterns of repeated body position change test had some differences.2) Compared with the pattern of HDT/HUT, the body can better adapt to the pattern of SUP/HUT impacting on the cardiovascular system3) The pattern of HDT/HUT may be used for astronaut selection; the pattern of SUP/HUT may be used for G warm-up maneuver before space flight.