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 expeditio ns: one involving a 16-d trip between 2000 m and 5600 m, followed by a 2-d ascent to 6440 m and back again; the other, a 21-d stay at 6542 m. We teste d 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 un der normoxia before the climb, under acute and chronic hypoxia during the c limb, and under normoxia after the climb. They were compared for two contro l groups tested only under normoxia. Results: The altitude stay was found t o have an effect on the 6542 m group when compared with the controls. Group performance differed at 2 d and 21 d after their arrival at 6542 m and aft er their return to normoxia. When all the test administrations were pooled together for this expedition we noted an interaction between the level of d ifficulty of the task and the experimental and control groups: namely the d ifference 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 5600 m ) when the group tested was compared with the controls. Conclusion: For a 2 1-d stay at an altitude of 6542 m with the same ascent protocol as a group climbing to a lower altitude (16 d between 2000 m and 5600 m followed by a 2 d ascent to 6440 m and back again), subjects appeared to suffer from atte ntional performance deficits which persisted for several days after the sub jects returned to normoxic conditions.