AIM:This study continuously monitors the hemodynamic changes in conscious and anesthetic rats during rapid ascent to high altitude to investigate whether there is difference between the 2 conditions and discuss the rela-ted underlying mechanism.METHODS: Sprague-Dawley rats were randomly divided into conscious group, anesthetic group, anesthetic-5000-control ( A-5000-control) group, anesthetic-5000-aminoguanidine ( A-5000-AG) group, conscious-5000-control ( C-5000-control ) group and conscious-5000-aminoguanidine ( C-5000-AG ) group.The rats in anesthetic group and conscious group were kept in a hypobaric chamber, in which the simulated altitude was increased from 2 260 m to 5 000 m at 2 m/s, and the rats in other 4 groups were at 5 000 m.The system arterial pressure ( Psa) , central venous pressure ( CVP) , heart rate ( HR) and breathing rate ( BR) were directly and continuously displayed and digitally recorded by a high-performance data acquisition (PowerLab 16/35, AD Instruments) at 200 Hz.RESULTS: The HR and BR in the conscious rats were higher and MAP was lower than those in the anesthetic rats obviously.A significant decrease in mean arterial pressure ( MAP) in conscious and anesthetic groups was observed following the increase in the altitude levels, and the net decrease in MAP in conscious group was significantly greater.Additionally, HR in the conscious rats was sig-nificantly lower at 5 000 m than that of the initial level.The rats in C-5000-AG group and A-5000-AG group showed a sig-nificant increase in the arterial pressure after the intravenous injection of AG, a selective inhibitor of inducible nitric oxide synthase ( iNOS) , and no marked change of HR and BR was found.CONCLUSION: Blood pressure and HR decrease during rapid ascent to high altitude, while the change of BR is not obvious.The mechanisms of self-safety would be trig-gered in the early stage of hypoxia, which activates iNOS and then leads to a larger number of nitric oxide.Plentiful NO di-astolizes the vessels to improve the ventilation-perfusion mismatch and lower the blood pressure.When the altitude arise to 5 000 m, even more earlier, a decompensatory stage may occur in the body, leading to decreased HR and blood pressure further more than those in the anesthetic rats.Due to the effects of pentobarbital sodium, the depression of blood pressure requires a lag period and the net decrease in MAP is less than that in the conscious rats.Therefore, hemodynamic changes during rapid ascent to high altitude in conscious rats are more comprehensive and authentic.