Effects of different stay durations on attentional performance during two mountain expeditions

BACKGROUND: Hypoxia-induced deficits in intellectual performance are linked to the altitude level reached, the speed of the ascent and the time spent at high altitude. This study analyzes attentional changes during adaptation to two different types of stay at high altitude on two different expeditions: one involving a 16-d trip between 2,000 m and 5,600 m, followed by a 2-d ascent to 6,440 m and back again; the other, a 21-d stay at 6,542 m. We tested the hypothesis that, at similar high altitudes, decrements in attentional performance would only occur during a long duration stay. METHODS: Indexes for attentional performance were calculated for two experimental groups under normoxia before the climb, under acute and chronic hypoxia during the climb, and under normoxia after the climb. They were compared for two control groups tested only under normoxia. RESULTS: The altitude stay was found to have an effect on the 6,542 m group when compared with the controls. Group performance differed at 2 d and 21 d after their arrival at 6,542 m and after their return to normoxia. When all the test administrations were pooled together for this expedition we noted an interaction between the level of difficulty of the task and the experimental and control groups: namely the difference between the groups was greater for the difficult task than it was for the easy task. No effect was found for the other expedition (at 5,600 m) when the group tested was compared with the controls. CONCLUSION: For a 21-d stay at an altitude of 6,542 m with the same ascent protocol as a group climbing to a lower altitude (16 d between 2,000 m and 5,600 m followed by a 2 d ascent to 6,440 m and back again), subjects appeared to suffer from attentional performance deficits which persisted for several days after the subjects returned to normoxic conditions.