Effects Of Lower Body Negative Pressure In The Upright Seated Position On The Human Physiological And Psychological Function

G-LOC means the G -induced loss of consciousness when a pilot is exposed to +Gz. In recent years, with the development of high-performance fighter planes, the defense against high sustained +Gz load(>9 G) with great jerk(>6 G/s) ,as well as the prevention and monitoring of G-LOC becomes an important subject of how to improve the fighting capacity of the air force. At the present time, how to decrease the incidence of G-LOC and how to prevent occurrence of flying accident still remains one of the important subjects for aerospace medical workers.Lower body negative pressure( LBNP) is one of the effective methods to simulate the influence of gravito-inertial force on human circulation. It can simulate the effects of +Gz on human body to a certain extent. Considering thehigh-technology war in he future and the specific condition of the air force, it is necessary to investigate the effect of LBNP on blood flow in cerebral artery and brain cognitive ergonomics in order to monitor the G-LOC.The main objectives of this experiment were: I) To observe the effects of lower body negative pressure in upright seated position(U-LBNP) on human blood flow velocity in middle cerebral artery (VMCA), heart rate(HR) and blood oxygen saturation (SaO2). 2) To investigate the effects of different U-LBNP on human event related potentials(ERP), reaction time(RT), tracking error (ER) and cardiovascular function. The results of this experiment might provide experimental data for diagnosis of presyncope and orthostatic intolerance.In this study, 13~15 young men were chosen as subjects. Five minutes before the experiments, the subjects were tested , the data coming out of which were used for contrast. During the experiments, each subject participated 2 tests, each test lasting 5 minutes with 2 different levels of U-LBNP respectively. These LBNP were:-4.00 kPa(-30mmHg) and -6.67 kPa(-50mmHg).In experiment one, 15 young men were selected as subjects. VMCA, HR and Sa(>2 were measured at 0.5, I, 2, 3, 4, 5 min during U-LBNP and l,3,5min after U-LBNP of-4.00 kPa and -6.67 kPa .In experiment two,13 young men were selected as subjects. Amplitude of P30o (AMP), latency of P30o(LAT), RT , ER, HR and blood pressure(BP) were measured during U-LBNP of-4.00 kPa and -6.67 kPa.The main results were as follows:I. Under -4.00 kPa U-LBNP, VMCA slowed down at 4,5min during U-LBNP(/><0.05) , and HR speeded up at 3,4,5min during U-LBNP(P<0.05). There were no significant changes of SaO2. Under -6.67 kPa U-LBNP, VMCA became slow at 2,3min duringU- LBNP(P<0.05), and at 4 min and 5 min duringU-LBNP(PO.Ol). At 1 min after release of U-LBNP, VMCA did not recover (P<0.05). Thereafter it recovered to the control level. HR significantly increased during U-LBNP(.P<0.01) and SaOj decreased obviously at 5 min during U-LBNP(P<0.01).2. Under -4.00 kPa U-LBNP, AMP and LAT RT , ER and BP had no significant differences compared with control level, whereas HR increased at 3,5min during LBNP(P<0.01). Under -6.67 kPa U-LBNP, AMP decreasedOPO.05); LAT and RT delayed(P<0.05, PO.05); ER increasedCPO.05); HR speeded up(/><0.01); Diastolic pressure rose(P<0.05), but systolic pressure had no significant changes. After LBNP of -4.00 or -6.67 kPa was released, HR and BP recovered rapidly.The results of this study show that LBNP can cause blood pooling in lower body and decrease supply to brain blood. VMCA and brain blood volume decrease make the response to the outside stimuli slow down and the brain cognitive ergonomics decrease. Meanwhile the cardiovascular compensation function enhances, so HR speeds up and BP rises. The results of this study provide experimental data for diagnosis of presyncope and orthostatic intolerance.