High Altitude Pulmonary Edema
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High altitude pulmonary edema (HAPE) is a life threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above 2500m. Some cases have however been reported also at lower altitudes (between 1500 and 2500m in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high altitude exposure with a high mortality in absence of emergency treatment.
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[edit] Aetiology
The initial insult that causes HAPE is a shortage of oxygen which is caused by the lower air pressure at high altitudes.[1] The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:
- Increased pulmonary arterial and capillary pressures (pulmonary hypertension) secondary to Hypoxic Pulmonary Vasoconstriction.[2]
- An idiopathic non-inflammatory increase in the permeability of the vascular endothelium.[3]
Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension may not in itself be sufficient to explain the development of oedema: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.[4]
[edit] Incidence
The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~ 4,000 m) appears to be less than 1%. In over 30 years of research experience, the U.S. Army Pike's Peak Research Laboratory, utilizing about 300 sea-level resident volunteers (and more than 100 staff members) rapidly and directly exposed to high altitude, only 3 were evacuated with suspected HAPE.
[edit] Predisposing factors
Individual susceptibility to HAPE is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE).
[edit] Research
In order to help understand the factors that make some individuals susceptible to HAPE, the International HAPE Database was set up in 2005.[5]
[edit] Footnotes
- ^ Kenneth Baillie and Alistair Simpson. Barometric pressure calculator. Apex (Altitude Physiology EXpeditions). Retrieved on 2006-08-10. - Online calculator
- ^ Bärtsch P, Maggiorini M, Ritter M, Noti C, Vock P, Oelz O (Oct 31 1991). "Prevention of high-altitude pulmonary edema by nifedipine.". N Engl J Med 325 (18): 1284-9. PMID 1922223.
- ^ Swenson E, Maggiorini M, Mongovin S, Gibbs J, Greve I, Mairbäurl H, Bärtsch P (2002). "Pathogenesis of high-altitude pulmonary edema: inflammation is not an etiologic factor.". JAMA 287 (17): 2228-35. PMID 11980523.
- ^ Maggiorini M, Mélot C, Pierre S, Pfeiffer F, Greve I, Sartori C, Lepori M, Hauser M, Scherrer U, Naeije R (2001). "High-altitude pulmonary edema is initially caused by an increase in capillary pressure.". Circulation 103 (16): 2078-83. PMID 11319198.
- ^ International HAPE database. Apex (Altitude Physiology EXpeditions). Retrieved on 2006-08-10.
