Countermeasures To Orthostatic Intolerance After Space Flight

Over the tens of years of human space flight experience, long-term aviationcould result in a series of physiological changes, especially cardiovascularfunction disorders. All astronauts experienced some degree of orthostaticintolerance following spaceflight, ranging from tachycardia to orthostatichypotension and syncope. these effected the work ability and health ofastronauts, and re-entry or landing. Therefore, to provide additional protectionagainst spaceflight-induced orthostatic intolerance during re-entry and landingwas very necessary.Nowadays, a variety of countermeasures have been developed, includingsaline loading, intermittent venous pooling (using lower body negative pressure,LBNP), pharmacological manipulations and training. But these countermeasureshave not been complete effective, most astronauts experienced some degree oforthostatic intolerance. However, with the further development of aerospacetechnology, human missions to Mars and deep space exploration will become a reality, astronauts will face more severe space environment effects. So, furtherimprovement and research for countermeasures will be an important task ofaerospace medicine.We designed heel raising which combined anti-G straining maneuver andcountermeasure for vasovagal syncope. Then to verify the efficiency of heelraising on orthostatic tolerance. At the same time, to evaluate the effectivepressures of two anti-G suits which aim to improve lower body negativepressure （LBNP） tolerance. The purpose of this study was to makecountermeasures to orthostatic intolerance and to provide a theoretical basis forpreventing postflight orthostatic intolerance in long-duration spaceflight.The main results and findings of this study were as follows:1. Heel raising may be beneficial for lower body negativepressure tolerance We observed and compared the lower body negativepressure(LBNP) tolerance of subjects underwent orthostatic stress tests ofcombined head-up tilt and LBNP. The one test determined the baseline LBNPtolerance (control group); In another test, subjects were instructed to heel raisinguntil presyncope or syncope. Beat-by-beat arterial blood pressure was measuredduring the study and compared the changes of cardiac function. The resultsshowed that as compared with those of control group, the duration of negativepressure(DNP) and cumulative stress index(CSI) increased (P<0.05) when heelraising was conducted; mean arterial pressure and stroke volume increasedsignificantly during LBNP of-40mmHg and-50mmHg phase (P<0.05) in heelraising group, compared with the control group. The increment of heart rate inheel raising group was significantly lower during LBNP of-40mmHg and-50mmHg phase (P<0.05) as compared to the control group. It is suggested that heel raising increases human LBNP tolerance and improves the cardiovascularfunction.2. Inflatable anti-G suits may be beneficial for lower bodynegative pressure tolerance We observed and compared the effects of theinflatable anti-G suit on LBNP tolerance at two level of pressure. The purpose ofthis study was to evaluate the effective pressures which aim to LBNP tolerance.Beat-by-beat arterial blood pressure was measured during the study andcompared the changes of cardiac function underwent the two effective pressures.The results showed that the pressure of inflatable anti-G suit were set at30~40mmHg or40~50mmHg. As compared with those of control group, whenwearing inflatable antigravity suit under two pressure standard, the DNP andCSI increased (P<0.01); During LBNP exposure, MAP and SV tend to increasedand HR at40~50mmHg declined, but no significant changes were observed. It issuggested that the inflatable anti-G suits can increase LBNP tolerance when athigh and low level of pressure respectively and improve cardiovascular function.At high level of pressure, this effect is more significant.3. Lacing anti-G suits may be beneficial for lower bodynegative pressure tolerance We observed and compared the effects of thelacing anti-G suit on LBNP tolerance at two level of pressure. The purpose ofthis study was to evaluate the effective pressures which aim to LBNP tolerance.Beat-by-beat arterial blood pressure was measured during the study andcompared the changes of cardiac function underwent the two effective pressures.The results showed that the pressure of lacing anti-G suit were set at20~30mmHg or30~40mmHg. As compared with those of control group, whenwearing lacing antigravity suit under two pressure standard, the DNP and CSI increased (P<0.01); During LBNP exposure, MAP and SV tend to increase andHR tend to decline, while no significant changes were observed. It is suggestedthat the lacing anti-G suits can increase LBNP tolerance when at high and lowlevel of pressure respectively and improve cardiovascular function. At high levelof pressure, this effect is more significant.In conclusion, we compared the effects of heel raising and two anti-G suitson LBNP tolerance and cardiac function, and found that heel raising and the twoanti-G suit can increase LBNP tolerance and improve cardiovascular function.This study may be beneficial for prolonged spaceflight.