Date Published: October 3, 2018
Publisher: Public Library of Science
Author(s): Mirjam Limmer, Petra Platen, Andreas Mierau.
Exposure to hypoxic conditions is reported to impair cognitive performance. Further, moderate physical exercise improves cognitive function, but little is known about the influence of exercise on cognitive function in hypoxia. Therefore, the current study aimed to examine the influence of hypoxia (HYP) and prolonged exercise (EX) on attentional performance.
A total of 80 participants (female: n = 29; male: n = 51) were assigned to four groups: HYP + EX (n = 15), HYP (n = 25), EX (n = 21) and normoxia (NOR) (n = 21). The Frankfurt Attention Inventory—2 (FAIR-2) was performed at four testing points (day 1, 14, 16 and 18) to assess attentional performance. All groups completed a pretest (D1) and a follow-up test (D18). In HYP + EX conditions, the cognitive task was performed in a hypoxic state after prolonged exercise (D14: 3950 m, D16: 5739 m) during a mountain climb on Mt. Kilimanjaro. Participants in HYP were tested under intermittent hypoxia at rest in a hypoxic chamber (D14: 3500 m, D16: 5800 m), and those in EX were tested under normoxia after prolonged exercise during a 7-day backcountry ski hiking tour. NOR was a control group, and participants completed all tests under normoxia and at rest.
Hypoxia impaired the attentional functions performance value (PV) and continuity value (CV) for the HYP + EX (p = 0.000) and HYP (L: p = 0.025; K: p = 0.043) groups at 5739 m and 5800 m, respectively, but not the function quality value (QV). In contrast, the EX group did not exhibit changes in attentional function.
The current results suggest that attentional performance is impaired during extreme normobaric and hypobaric hypoxic exposure. We further conclude that greater cognitive impairment under hypobaric hypoxia during a mountain climb compared with normobaric hypoxia at rest is not caused by prolonged exercise, but may be influenced by other factors (e.g. low temperatures, dehydration, or sleep deprivation) that remain to be verified.
There is currently widespread interest in high-altitude activities internationally, including mountaineering, hiking and skiing . During altitude exposure, the oxygen partial pressure decreases exponentially with increasing altitude and the resulting hypoxic conditions lead to cognitive and physiological alterations caused by decreased O2 intake [2,3]. In 1925, early mountaineers reported impairment of mental skills and a reduced ability to concentrate during a high altitude mountaineering expedition . Recent studies investigating the effects of hypoxic conditions on cognitive functions have reported impairments in a range of cognitive abilities, such as memory [5,6], learning , reaction time [8,9] and decision making [6,7]. Cognitive impairment, particularly attentional dysfunction, has negative effects on high altitude mountaineering expeditions, including poor decision making and situation assessment, errors in perception of environmental events or cues, and distraction [2,10]. For instance, attention impairment and associated distraction from rope and safety management, weather observations, or changes in attention to climbing partners’ physical health could result in inappropriate decisions. Because of the risks associated with mountain conditions, impaired decision making can lead to falls, injuries, and death . However, there is a small but increasing body of evidence regarding the effects of high altitude on attention . One previous study reported an impairment of attention capacity at simulated altitudes between 3000 and 5000 m . Additionally, impaired attention is described for acute exposure to simulated altitude (4500 m) at a maximum of 24 h [1,12] and for environmental hypobaric hypoxia up to 5300 m . In contrast, one study reported attentional changes in mountaineers during a high altitude expedition involving a stay of 21 days at 6542 m, but not for a second group of mountaineers that stayed 18 days between 2000 and 6440 m .
We hypothesized that attentional performance would be impaired during a mountain climb up to 5800 m because of the effects of hypoxic conditions and prolonged exercise. In addition, we predicted that the potential moderators hypoxia and prolonged exercise would influence attention.
The present findings suggest that attention is impaired during extreme normobaric and hypobaric hypoxic exposure, with the strongest effects occurring during mountain climbs at extreme altitudes. Moreover, we conclude that greater cognitive impairment under hypobaric hypoxia during a mountain climb compared with normobaric hypoxia at rest does not appear to be caused by prolonged exercise. There are significant methodical testing challenges when testing for attentional impairments between simulated and real world altitude conditions. Thus, additional studies are required to standardize these methodical factors and identify additional factors besides hypoxia that negatively impact attention during mountain climbs, such as sleep deprivation, dehydration, or low temperatures at high to extreme altitudes.