Abstract
PurposeThe present study determined the association between body fluid variation and the development of acute mountain sickness (AMS) in adults.MethodsForty-three healthy participants (26 males and 17 females, age: 26±6 yr, height: 174±9 cm, weight: 68±12 kg) were passively exposed at a FiO2 of 12.6% (simulated altitude hypoxia of 4500 m, PiO2 = 83.9 mmHg) for 12-h. AMS severity was assessed using the Lake Louise Score (LLS). Food and drink intakes were consumed ad libitum and measured; all urine was collected. Before and after the 12-h exposure, body weight and plasma osmolality were measured and whole-body bioimpedance analysis was performed.ResultsThe overall AMS incidence was 43% (38% males, 50% females). Participants who developed AMS showed lower fluid losses (3.0±0.9 vs. 4.5±2.0 ml/kg/h, p = 0.002), a higher fluid retention (1.9±1.5 vs. 0.6±0.8 ml/kg/h, p = 0.022), greater plasma osmolality decreases (−7±7 vs. −2±5 mOsm/kg, p = 0.028) and a larger plasma volume expansion (11±10 vs. 1±15%, p = 0.041) compared to participants not developing AMS. Net water balance (fluid intake – fluid loss) and the amount of fluid loss were strong predictors whether getting sick or not (Nagelkerkes r2 = 0.532). The LLS score was related to net water balance (r = 0.358, p = 0.018), changes in plasma osmolality (r = −0.325, p = 0.033) and sodium concentration (r = −0.305, p = 0.047). Changes in the impedance vector length were related to weight changes (r = −0.550, p<0.001), fluid intake (r = −0.533, p<0.001) and net water balance (r = −0.590, p<0.001).ConclusionsParticipants developing AMS within 12 hours showed a positive net water balance due to low fluid loss. Thus measures to avoid excess fluid retention are likely to reduce AMS symptoms.
Highlights
Rapid ascents of non-acclimatized mountaineers to altitudes above 2,500 m are associated with the development of acute mountain sickness (AMS).This normally self-limiting syndrome is characterized by non-specific symptoms such as headache, dizziness, nausea, vomiting, loss of appetite, fatigue, and insomnia [1,2]
Changes in fluid balance have been reported to be different between hypobaric hypoxia vs. normobaric hypoxia conditions suggesting that both, reduced barometric pressure and oxygen partial pressure contribute to fluid retention [20]
Plasma osmolarity (Posm), sodium (Na), resistance divided by body height (R/height), reactance divided by body height (Xc/height)
Summary
Rapid ascents of non-acclimatized mountaineers to altitudes above 2,500 m are associated with the development of acute mountain sickness (AMS).This normally self-limiting syndrome is characterized by non-specific symptoms such as headache, dizziness, nausea, vomiting, loss of appetite, fatigue, and insomnia [1,2]. Controversy exists whether other factors such as low fluid intake and dehydration [6,9,10] or overhydration [11,12] promote AMS because of the lack of agreement in other studies [13,14,15]. These divergent findings may be explained by varied experimental designs (e.g., laboratory vs field studies, resting vs exercise conditions) and the lack of well controlled studies [15]. Assessment of fluid homeostasis during passive normobaric hypoxia exposure (i.e., controlled normobaric hypoxic conditions, without the influence of exercise, hypobaria, cold) might help to clarify the pathophysiological relevance of hypoxia on the hydration status and the concomitant AMS development
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