Comparison of the effects of chronic intermittent hypobaric hypoxia and continuous hypobaric hypoxia on hemodynamics in rats.

The aim of this study is to investigate the effects of chronic intermittent hypobaric hypoxia (IHH) and chronic continuous hypobaric hypoxia (CHH) on hemodynamics under basic normoxia and acute hypoxia conditions and to find the difference of two types of chronic hypoxia. Forty adult male Sprague-Dawley (SD) rats were randomly divided into 5 groups: Control group (CON), 28 days IHH group (IHH28), 42 days IHH group (IHH42), 28 days CHH group (CHH28) and 42 days CHH group (CHH42). The rats in IHH groups were treated with intermittent hypoxia (11.1% O2) mimicking 5 000 m altitude in a hypobaric chamber for 28 or 42 d, 6 h a day, respectively. The rats in CHH groups lived in the hypobaric chamber with the same degree of hypoxia like IHH rats except half an hour in normoxia each day for feeding and cleaning. The body weight of rats was measured once a week. The parameters in hemodynamics, such as mean artery blood pressure (MAP), heart rate (HR), left ventricular systolic pressure (LVSP), maximum change rate of left ventricular pressure (+/-LVdP/dt(max)) were recorded under basic normoxia and acute hypoxia conditions through catheterization technique. The superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in myocardium of rats were measured by biochemical method. The weights of whole heart, left and right ventricles were measured separately. The results showed: (1) The basic HR and MAP in CHH42 rats were lower than those in CON, IHH and CHH28 rats (P<0.05). (2) IHH showed a cardioprotection against acute hypoxia and reoxygenation injury, manifested as the result that the changes of HR, MAP, LVSP, and +/- LVdP/dt(max) were smaller than those in CON rats during acute hypoxia and reoxygenation. CHH showed a rather strong cardioprotection during acute hypoxia, manifested as the result that the decreases of HR, MAP, LVSP, and +/- LVdP/dt(max)were much smaller, but it did damage during reoxygenation, manifested as the result that the recovery of hemodynamics was the worst among three groups (P<0.05). (3) The antioxygenation of heart was increased in both IHH and CHH rats compared with that in CON rats manifested by the increased SOD activity and decreased MDA content (P<0.05, P<0.01). (4) IHH had no effect on heart weight, but CHH rats showed an obvious right ventricular hypertrophy compared with CON and IHH animals (P<0.01). The result indicates that IHH can induce a more effective cardioprotection with no much side effect, which might have a potential value for practical use.