FIG. 1.

Illustrative nocturnal oxygen profiles at high altitude. S_pO₂ versus time (hours) for illustrative nocturnal sleep recordings during the first night at HA. Top panel (A) illustrates the trace of a representative subject with intermittent hypoxemia with relatively high mean S_pO₂. Middle and bottom panels (B, C) exhibit different nocturnal S_pO₂ tracings of representative subjects from subgroups with marked and mild reductions in mean S_pO₂ and no significant sleep apnea, respectively. Red line shows the mean nocturnal S_pO₂ during the night. AHI values are reported for each tracing. AHI, Apnea–Hypopnea Index; HA, high altitude; S_pO₂, oxyhemoglobin saturation.