“Acute mountain sickness (AMS) is a syndrome induced by hypoxia in unacclimatized individuals who ascend rapidly to altitudes exceeding 2500m and remain there for more than several hours” (Beidleman, et al., 2003, p. 322). AMS typically occurs when an individual is exposed to reduced air pressures and lower oxygen concentrations, which is most often encountered at high altitudes (Heller, 2009). “Oxygen is critical to normal cellular function because it is an essential part of the electron transport chain for energy production in cells” (West, 2004, p. 790). The first account of mountain sickness was documented in 1590 by Jose do Acosta, a Spanish Jesuit, in his book, Historia Natual y Moral de las India (Virués-Ortega, Garrido, Javierre & Kloezeman, 2006). AMS is diagnosed and classed according to the Lake Louise AMS assessment score (Vardy, Vardy & Judge, 2005). The clinical diagnosis of AMS is made in the setting of recent ascent combined with two associated symptoms, based on the consensus of 1991 International Hypoxia Symposium at Lake Louise, Canada as described in Figure 1 (Hou, Lin & Wang, 2004).
The AMS assessment includes five symptoms: headache, gastrointestinal distress, fatigue or weakness, dizziness or light-headedness, and difficulty sleeping (Wagner, Fargo, Parker, Tatsugawa & Young, 2006). Each symptom is scored on a scale of 0 (not present) through 3 (severe or incapacitating) (Wagner et al., 2006). Symptom scores are combined, resulting in a range from a minimal assessment score of 0, to a maximal score of 15 (Wagner et al., 2006). The preferred assessment method is a headache with one other symptom and a total score of three or more (Wagner et al., 2006). AMS typically resolves spontaneously within 1 – 3 days of acclimatization to the new altitude if no further ascent occurs (Bärtsch & Saltin, 2008), or upon descent to a lower altitude. If symptoms are ignored and ascent continues, the life threatening conditions, High-Altitude Cerebral Edema (HACE) or High Altitude Pulmonary Edema (HAPE) can develop. HAPE accounts for most fatalities from high altitude illnesses and occurs to 5 to 10% of AMS patients (Hou et al., 2004).
When humans are exposed to environmental hypoxia, homeostatic changes occur at both the systemic and cellular levels to restore adequate oxygenation and minimize hypoxic injury. This acclimatization process demonstrates the systemic effects of isolated hypoxia and the predominate hematological, respiratory, and cardiovascular responses. Emerging evidence indicates that the hypoxia-inducible factor (HIF) family of transcription factors plays a central regulatory role in these homeostatic changes (Smith, Robbins & Ratcliffe, 2008).
The most widely known feature acclimatization is the development of polycythaemia which improves the oxygen-carrying capacity of the blood (Smith et al., 2008). However, it develops slowly and takes several days before an increased rate of erythrocyte production can be...