[Myocardial ultrastructural changes in rats following different levels of acute +Gz exposure].

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.

[Assessment of autonomic nervous function during orthostatic stress in pilots with history of syncope].

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.

Study of Some Endocrine Hormone in Pilots under Coriolis Acceleration Stimulation

OBJECTIVE: To explore the difference of some endocrine hormore of healthy pillots and the orthostatic intolerance pilots with coriolis acceleration Increased. METHODS: The coriolis acceleration of 3.75 pai 2cm/s2, 5.00 pai 2cm /s2, 6.25 pai 2cm/s2, was given with a Interval of 3-4 min In 12 flying syncope and 12 healthy pilots, AT-II, Isulin Cortisol, Aldosterone, Gastric were measured by radio immunossay. RESULT : All polits Showed that Aldosterone, AT-II, Gastrin were increased with coriolis acceleration Increased (p<005). Cortisol, Insulin of healthy pilots Increased (p<0,05). CONCLUSIONS : It was considered that endocrine hormone may be used In the autonomic nervous system evaluation Excitation of the autonomic nervous system ol healthy pilots were increased with coriolis acceleration acted, but the orthostatic intolerance pailots decrease.