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Objective: To observe the effects of different levels of acute +Gz exposure on myocardial ultrastructure of rats and provide experimental basis for further development of anti-G measures., Method: Twenty male Wistar rats were randomly divided into 4 groups (n=5): normal control group, +20 Gz group, +10 Gz group and +5 Gz group. Profile of the centrifuge +Gz exposure was trapezoidal, in which +20 Gz lasted for 30 s, +10 Gz for 1.5 min. +5 Gz exposure was repeated for 3 times with 30 min interval and each for 1.5 min. Myocardial tissue of left ventricle was sampled for transmission electron microscopy 5 h after exposure., Result: +20 Gz and +10 Gz exposure caused obvious edema of myocardial and endothelial cells, myofibril disorder and injuries of mitochondria and nucleus. Breaks of myocardial fiber, formation of contraction bands and rupture of mitochondria were also observed in +20 Gz group. In +5 Gz group, there was still slight edema of myocardial and endothelial cells, while organic changes of myocardial ultrastructure were not observed., Conclusion: High +Gz exposure can cause myocardial ultrastructural injury in rats. Slight reversible injured response can also be observed in myocardial cell after repeated moderate level of +Gz exposure. This indicates that attention should be paid to the study of the effect of high +Gz on heart in pilots.

Objective: To assess the role of autonomic nervous function during orthostatic tolerance tests (OTT) in pilots with history of G-induced loss of consciousness (G-LOC) or vasovagal syncope (VVS)., Method: The relation between heart rate variability (HRV) and outcome of OTT result were compared among 3 groups of cases: 1) 30 patients with history of syncope and positive OTT as patient group (PG); 2) 20 cases with history of syncope but negative OTT result as negative group (NG); 3) 15 age-, sex-, flight plane model-, flight time-matched healthy pilots as healthy control (HC). OTT results and HRV, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) before and after OTT and their time and frequency domain were compared and analyzed among the three groups., Result: HR, SBP, and DBP were not significantly different (P>0.05) among the three groups before OTT. But during OTT, HR in PG was higher than those in NG and HC (P<0.01), SBP and DBP in PG were lower than those in NG and HC (P<0.01). 24 h continuous RR interval standard difference (SDNN), HRV triangle index (HRVI), and interval average value in PG were significantly lower than those in NG and HC; Power spectrum analysis of mean 1 h value for low frequency part (LF) and high frequency part (HF) were not significantly different among three groups, but LF/HF ratio in PG was higher than that in NG or HC (P<0.05)., Conclusion: It is suggested that G-LOC and VVS may be due to increase in sympathetic tone and decrease in parasympathetic tone during orthostatic stimulation, as resulted from autonomic nervous dysfunction.

Objective. To investigate the preventive and theralseutive (therapeutic) effects of basic fibroblast growth factor (bFGF) and Radix Salviae Miltiorrhizae (RSM) on brain injury caused by repeated +Gz exposures. Method. bFGF and RSM were injected intraperitoneally into SD rats before and after repeated +Gz exposures. The contents of excitatory amino acids (EAAs), nitric oxide (NO) and the number of cell apoptosis in the brain were measured, and were compared to those of the control group and normal saline (NS) group. Result. The contents of EAAs, NO and the number of cell apoptosis were significantly higher in repeated +Gz exposures group than those in control group. The values were markedly lower in bFGF and RSM group than those in repeated +Gz exposures group and NS group. Conclusion. bFGF and RSM showed distinct preventive and therapeutic effect on the brain injury induced by repeated +Gz exposures.

Objective: To study the relationship between cardiac arrhythmias and autonomic nervous regulation in pilots under +Gz acceleration., Method: Dynamic ECG during +Gz exposures in 36 orthostatic intolerance pilots and 62 healthy pilots were analysed and compared., Result: The orthostatic intolerance pilots had obviously lower +Gz tolerance and more cardiac arrhythmias. The cardiac arrhythmias could affect +Gz tolerance., Conclusion: The cardiac arrhythmias under +Gz acceleration could be taken as an index of evaluating cardiovascular compensatory function and warning against acceleration (+Gz) induced loss of consciousness (G-LOC).

Objective. To study changes of mRNA expression of IL-1beta and TNF-alpha in rat brains after repeated exposures to +Gz. Method. Twenty conscious SD rats served as the subjects. They were randomly divided into 5 groups. Using an animal centrifuge, control rats (n = 4) were exposed to +1 Gz and experimental rats (n = 16) were exposed to +14 Gz three times, each for 45 s with 30 min interval in between. The rat brains were taken 30 min, 6 h, 24 h and 48 h after the last centrifuge run and total RNA was isolated. mRNA expression levels of IL-1beta and TNF-alpha in rat brain were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Result. mRNA expression levels of IL-1beta and TNF-alpha in rat brains taken 30 min, 6 h and 24 h after repeated +Gz exposures were significantly higher than those in control rats, but returned to normal after 48 h. Conclusion. It suggested that mRNA expressions of IL-1beta and TNF-alpha in rat brains can be stimulated by repeated +Gz exposures and the increased expression of IL-1beta and TNF-alpha may play a role in the pathologic course of brain damage induced by +Gz exposures, but the damage is reversible.

Objective: To study the changes of mRNA expression of heat shock protein 70 (HSP70) in the rat brain exposed to repeated +Gz., Method: The mRNA expression levels of HSP70 in rat brain were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR)., Result: The HSP70 mRNA expression levels in rat brains taken 30 min and 6 h after repeated +Gz exposures were significantly higher than those in control group, while the difference between the levels of control group and those of experimental rat brains taken 24 h after +Gz exposure was not significant., Conclusion: It is suggested that HSP70 mRNA expression in rat brain can be induced by repeated +Gz exposures and the increased HSP70 mRNA expression may play an important role in self-protection against brain damage induced by +Gz exposures.