Figure 1From: Effects of acute hypoxia on heart rate variability, sample entropy and cardiorespiratory phase synchronization Experimental protocol described with a diagram showing altitude vs. time. Each subject stayed at each simulated altitude for 15Â minutes. The physiological data of the last 10Â minutes was considered as steady state and adopted for analysis. The simulated altitude ascended from sea level (SL) to 3000Â m and 3000Â m to 4000Â m at the rate of 3Â m/s.Back to article page