Abstract： Objective To monitor physiological indexes of divers in simulated different high altitude helium-oxygen (heliox) diving,and also to explore the effect of different high-altitude diving and physical load on the cardiopulmonary function of divers.Methods In the dual-purpose hyperbaric-hypobaric chambers,4 divers were exposed to simulated altitudes of 50 (plain),3000,4000 and 5200 m for a succession of 9 days.The divers stayed at 50,3000 and 4000 m for 2 days respectively,but at 5200 m they stayed for 3 days.At 3000 and 4000 m,the divers conducted 30 m simulated dives,once a day.On the first day at 5200 m,the divers carried out a 30 m simulated dive,and on the second day a 50 m dive,but on the third day no diving activity was conducted.The duration of diving was all 60 minutes.Heart rate and stroke volume of the divers were detected every morning,after they sat at ease for 10 minutes.Heart rate,arterial oxygen saturation (SaO2) and exhaled end CO2 volume were measured after the divers took 1 min rest on the treadmill.Then,the divers had 5-minute treadmill exercise with load of 0.5 kg and speed of 60r/min.The pace of exercise was measured with a pacemeter,and heart rate and SaO2 at the end of each minute were detected for a succession of 5 minutes.After exercise,the divers sat at ease on the treadmill,and heart rate,SaO2 and exhaled end CO2 volume were recorded at the end of each minute for a succession of 3 minutes.Every afternoon,the divers carried out simulated dives,during which heart rate was monitored.(No diving at the plain,but the physiological indexes was measured,which was used as basic value).Change value of heart rate was the heart rate at the 5th minute subtracted by the recovery heart rate at the 3rd minute.The maximal oxygen uptake (VO2max) was thus calculated according to heart rate by using the Astrand P.O nomogram.Results (1) When the simulated 30 m dive was performed at the altitudes of 3 000 and 4 000 m,the heart rates of the divers decreased by 9.6％ and 6.9％ respectively,as compared with those of the same altitudes without dive.Likewise,when the simulated 30 and 50 m dives were conducted at the altitude of 5200 m,the divers' heart rates decreased by 7.6％ and 8.0％ respectively,as compared with those of the same altitude without dive.Heart rates at various high altitudes during the dives tended to decrease,when they were compared with those at the same high altitudes without dives,and statistical significance could be noted,when comparisons were made between them (P ＞0.05).The stroke volume at 3 000 m [(68.1± 15.8) ml] was significantly lower than that at 50 m [(84.72 ± 22.7) ml],with statistical significance (P ＜ 0.05).(2) Heart rates at various high altitudes were significantly higher than that at the plain (50 m),no matter whether the divers were at rest,with physical load or during the stage of recovery,also with statistical significance (P ＜ 0.05 or P ＜ 0.01).No statistical significance could be noted in changes of heart rates,when heart rates of the divers at 4 000 m were compared with those at 5 000 m (P ＞ 0.05).(3) With the elevation of altitudes,SaO2 levels at different altitudes decreased progressively,and statistical significance could be seen when comparisons were made between them(P ＜0.05 or P ＜0.01).(4) VO2max at 3000,4000 and 5200 m decreased by 6.2％,19.9％and 22.3％ respectively,when compared with that at the plain.(5) When the divers were at rest,CO2 level in the exhaled end-tidal air at 5200 m decreased significantly than that at the plain,with statistical significance (P ＜0.01).When compared with that at the plain,CO2 levels in the exhaled end-tidal air at the end of 3 minutes during recovery at 3000,4000 and 5200 m decreased significantly,also with statistical significance (P ＜0.01).Conclusions Following simulated helium-oxygen diving at high altitudes,the cardiopulmonary function of the divers improved to a certain extent,with the tendency of turning for the better.