Study On The Method Of Simulated Push-pull Effect And Training Programs For Counteracting Push-pull Effect

The mechanism, early-warning and countermeasures of G-LOC are crucial problems in aviation medicine. When combat aircraft flew for fight or training, the aircrew were exposed frequently to less than +1Gz acceleration during tactical maneuvering. On an immediate transition to high-sustained +Gz levels, +Gz tolerance were decreased by previous baseline zero or -Gz exposure. This phenomenon was defined as"push-pull effect, PPE". The impairment of +Gz tolerance was directly related to the magnitude and duration of the preceding -Gz exposure. According to the demands of attacking flight maneuvering and the development of high performance aircrafts, alternations of±Gz and PPE will have more chances to appear in real flight which bring great challenges to the flight safety. Therefore, study on PPE became to be a new hotpot in the research field of aviation medicine.Normally, modern fighter aircrafts did not expose to high level sustained–Gz in combat flight. But push-pull maneuver may be used in some fighting maneuverings, such as dive and missile escape. Though the emergence of -Gz in military flight was less, smaller and shorter than those of fly aerobatics, more consideration must be given to the associated impairment of subsequent +Gz tolerance.Classic viewpoints to the mechanism of PPE were the blood head forward transferring and hydrostatic forces increase in vessel above heart-level. The consequences are immediate slowing of heart rate, decreased cardiac output and total peripheral resistance and reduction of arterial blood pressure. When transition to high-sustained +Gz levels, the time-course of BP recovery was prolonged to a greater extent due to the lengthened time course of sympathetically mediated peripheral vasoconstriction and impaired compensation of cardiovascular. Recent several studies suggested that autonomic reflexes and essential characteristic of slow vasoconstriction or rapid vasodilatation of peripheral vascular may contribute to the push-pull effect.Several equipments or techniques have been set up to simulate push-pull maneuver and to study the physiological effect of PPE, which included manned centrifuge, Coriolis acceleration platform, vertical rotating model, tilt table and perfusion circuit. Now in air force, besides increasing awareness of this potential hazard among pilots and doing pilot's best to avoid push-pull maneuvers, there were no special equipments and techniques to counteract the push-pull effect.In this study, we tried to set up new ground training programs to counteract push-pull effect. First of all, we established a new way to simulate push-pull maneuver by using tilt table combining with lower body negative pressure(LBNP). Then, we observed the alterations of cardiovascular after tilt table combining with LBNP training, repeated body position change training and self-generating lower body negative pressure training. Furthermore, we evaluated the possible functions of these three training programs on counteracting the push-pull effect.The main results and findings of this work were as follows:1. Cardiovascular reflex during push-pull maneuver simulated by tilt table combining with LBNP. This study used tilt table combining with -70mmHg LBNP to simulate push-pull maneuver and observed the changes of heart rate(HR), blood pressure(BP) and cardiac pump function during pure +90°head-up tilt(HUT-control) and +90°HUT preceded by various head-down tilt(HDT) angles. The results showed that systolic blood pressure(SBP), diastolic blood pressure(DBP), mean blood pressure(MAP) and total peripheral resistance(TPR) during HUT preceded by various angles of HDT decreased significantly(P<0.05) compared to HUT-control. These alterations related with the degree of HDT angles. Stroke volume(SV) and cardiac output(CO) during HUT preceded by all HDT conditions increased significantly(P<0.05) compared to HUT-control. SBP, DBP and MAP during HUT preceded by various angles of HDT changed insignificantly while push-pull maneuver simulated by tilt table combining with LBNP. However, SV, CO increased significantly(P<0.05) and TPR depressed significantly(P<0.05) below baseline, the magnitude of alterations related with the HDT angles. This results implicated that push-pull maneuver could be simulated by tilt table combining with LBNP, while BP changed variably to some extent.2. Cardiovascular reflex after repeated body position change training program HR, BP, cardiac pump function and autonomic reflexes during simulated push-pull maneuver, supine and HUT test were investigated after repeated body position change training for 1 time per day in 6 continuous days. The results showed that after training 6 days, BP and cardiac pump function trended to decrease, HFn increased and LFn decreased in heart rate variability analysis, baroreflex sensitivity (BRS) trended to decrease as compared to those before training. BP decreased significantly(P<0.05) in phase of HUT during simulated push-pull maneuver and HUT test, while cardiac pump function inclined to decrease after training 6 days. These results implicated that BP during simulated push-pull maneuver and the adjustive response ability to head-up tilt stress would decline after repeated body position change training because the proportion of HDT was greater than that of HUT. Thus, the repeated body position change training program was not fit for ground training to counteract push-pull effect. But its effect on decreasing BP implicated that it may be much more fit for astronaut training to ease space adaptation syndrome. 3 cardiac pump function and autonomic reflexes during simulated push-pull maneuver, supine and HUT test were investigated after push-pull maneuver simulated by tilt table combining with LBNP training for 1 time per day in 6 continuous days. The results indicated that after 6 days'training, SBP on supine position didn't change remarkably, while DBP, MAP and TPR trended to decrease and SV, CO increased as compared to those before training. HFn decreased and LFn, LF/HF increased in HRV analysis, BRS and LFn of systolic blood pressure variability (SBPV) trended to decrease. BP trended to decline in phase of HUT during simulated push-pull maneuver and HUT test, while cardiac pump function inclined to increase after 6 days'training. The results implicated that cardiac pump function strengthened and heart sympathetic tone increased after training for 6 days. But low TPR resulted from decreased peripheral sympathetic vasoconstriction tone reduced the adjustive response ability to head-up tilt stress. Thus, this training program for the purpose of counteracting push-pull effect needs to be modified and evaluated with much more works.4. Cardiovascular reflex after self-generated lower body negative pressure training program HR, BP, cardiac pump function and autonomic reflexes during simulated push-pull maneuver, supine and HUT test were investigated after self-generated lower body negative pressure training for 1 time per day in 10 continuous days. The results showed that after training for 10 days, BP and cardiac pump function on supine position increased significantly as compared 3. Cardiovascular reflex after push-pull maneuver simulated by tilt table combining with LBNP training program HR, BP, with those before training. HFn trended to decrease and LFn trended to increase. Results of SBPV analysis and BRS kept on the levels of those before training. BP and cardiac pump function increased significantly (P<0.05) in phase of HUT during simulated push-pull maneuver and HUT test as compared with those before training. The results indicated that basic cardiovascular level could be enhanced after self-generated lower body negative pressure training and the adjustive response ability to head-up tilt stress increased. This new training device and its training program could be adapted to anti-G training, including training to counteract push-pull effect, for pilots.In conclusion, this study established a new way to simulate push-pull maneuver using tilt table combining with LBNP and observed changes of cardiovascular after tilt table combining with LBNP training, repeated body position change training and self-generating lower body negative pressure training. This work found that the repeated body position change training program was not fit for ground training to counteract push-pull effect and simulated push-pull maneuver using tilt table combining with LBNP training program needs to be modified and evaluated in later works. While self-generating LBNP training program suited to counteracting push-pull effect. The results of this work may contribute to the studies on special acceleration training programs to fulfill the needs of air force.