Fig 2. Changes of heart rate, pulse oxygen saturation, and brain oxygen saturation.

The heart rate (HR) declined gradually after a rise during the stay at high altitude. Even at the sixth point, about 1 month after coming back to the 500m altitude, it continued to decrease. Pulse oxygen saturation (SPO₂) displayed a downward state at high altitude, although it increased at 1 and 3 months post arriving at the base camp. The left and right brain oxygen saturation increased at the second, third, and fourth point, which was significantly higher than that at the first point. At the fifth and sixth point, left brain oxygen saturation nearly returned to normal, while the right brain oxygen was still at high level. *, p<0.05 compared with the first point; **, p<0.01 compared with the first point; #, p<0.05, compared with the second point; ##, p<0.01, compared with the second point; ΔΔ, p<0.01, compared with the third point.