Effects of hyperbaric oxygen preconditioning on maximal oxygen uptake and walking-up the stairs index of the subjects when exposed to simulated 4 000 m acute hypoxia

Objective To investigate the effects of hyperbaric oxygen preconditioning (HBOP) on maximal oxygen uptake(VO2max)and walking-up the stairs index of the subjects with acute high altitude exposure. Methods At day 1, 8 subjects had walking-up the stairs exercise at the sea level for five minutes at a rate of 25 steps per minute, with the height of each step being 30 cm. A pacer was used to control the rate of walking up the stairs. Heart rate (HR), arterial oxygen saturation (SaO2), the amount of end expiratory CO2 were measured at rest and recovery stage, meanwhile heart rate and levels of SaO2 at exercise were also detected, with the obtained data being used as the control values at the sea level. At day 2, the subjects were exposed to the simulated 4 000 m high altitude and had the same walking-up the stairs exercise as day 1, with detected data being used as the control values at 4 000 m high altitude. At day 3 to 9, the subjects were exposed to HBO, once a day, 90 minutes per session. Half an hour after completion of HBOP at days 3, 5 and 7, the subjects were exposed to a simulated high altitude of 4 000 m and had the same walking-up the stairs exercise as day 1, and the subjects returned to the sea lever upon completion of the experiment. Maximal oxygen uptake (VO2max) and the walking-up the stairs indexes were calculated by heart rate. Results (1)At the instant after completion of 7th HBOP, the heart rate (158.82±9.08) decreased significantly, as compared with that of the control value at 4 000m [(167.58±7.63)beats/min], with statistical significance (P<0.05). (2)At the instant after completion of 7th HBOP, the walking-up the stairs exercise values(46.41±7.30)were increased significantly, as compared with those of the control value at 4 000 m(45.36±4.70)and the value detected at the instant upon completion of 5th HBOP(45.66±4.75)were increased significantly, also with statistical significance (P<0.05). (3)At the instant after completion of 7th HBOP, the value of VO2max was(46.41±7.30)ml/(kg·min) was obviously elevated, as compared with that of the control value at 4 000 m [(42.30±4.59)ml/(kg·min)], with statistical significance (P<0.05). (4)After 7th HBOP, the level of SaO2 at rest was(82.25±3.37)%, which was significantly increased, as compared with that of the control value at 4 000 m [(79.00±5.58)%], with statistical significance (P<0.05). The level of SaO2 at the instant after exercise, and the levels of SaO2 after completion of the 5th HBOP [(76.50±4.17)%] and 7th HBOP [(76.25±4.60)%] were obviously elevated, as compared with that of the control value at 4 000 m, also with statistical significance (P<0.05). Conclusions HBOP after acute high altitude exposure could increased maximal oxygen uptake and walking-up the stairs indexes and improve exercise capacity of the subjects at high altitude. Key words: Hyperbaric oxygen preconditioning; Simulated high altitude; Walking-up the stairs exercise; Maximal oxygen uptake; Walking-up the stairs index