Auswirkungen akuter Höhenexposition: Welche Höhe ist gesundheitlich verträglich?

Abstract

Exposures to natural and simulated altitudes are combined with a reduction of the available oxygen (hypoxia) and may provoke health problems or even emergencies. Although millions of people are living at high altitudes, are regularly or occasionally performing mountain sport activities, are transported by airplanes, and are increasingly frequently exposed to hypoxia at their workplace, e.g. with fire control systems, there is no consensus about the level of hypoxia which is well tolerated by most of human beings. Thus, the present mini review tries to define such a level. This review indicates that although humans show adaptive responses even to altitudes below 2000 m or corresponding normobaric hypoxia (FiO2: >16%) most of these subjects without severe pre-existing diseases well tolerate altitudes up to 3000 m (FiO2: 14.5%). If at all, symptoms of acute mountain sickness may develop in some persons after a minimum exposure time of about 6 hours. This also applies to children, elderly persons and pregnant women. Physical activity and unusual environmental conditions may increase the risk to get sick. Also patients with not severe cardiovascular, respiratory or metabolic diseases well tolerate such levels of altitude. However, individual differences in responses to hypoxia have to be considered and can at least partly be tested by simple hypoxia challenge tests. For safety reasons altitudes up to 2700 m or normobaric hypoxia up to FiO2 values of 15% are proposed to be well tolerated by most humans who are not severely diseased.

Controlled Hypoxia Acutely Prevents Physical Inactivity-Induced Peripheral BDNF Decline

“…Controlled hypoxia is known for its low risks and potential short and long-term benefits on physiological parameters (e. g., increased erythropoiesis, angiogenesis, antioxidant capacity, improved exercise performance) [24][25][26]46,47]. A recent review suggested that controlled hypoxia increases BDNF levels in the brain as well as in the blood of rodents [48].…”

“…In general the benefits and detriments of hypoxia are determined by the severity, frequency and duration of hypoxia exposures [24]. However, in the case of controlled hypoxia, e. g., in the context of altitude training, the reduction in the oxygen supply to the organism is mostly harmless [25]. An insufficient supply of O2 leads to a decrease in the O2 saturation of the blood (hypoxemia).…”

Effect of Intravenous Iron Supplementation on Acute Mountain Sickness: A Preliminary Randomized Controlled Study

“…An important clinical problem posed by this research is whether iron deficiency may increase susceptibility to AMS or other high-altitude diseases. Although some treatments have been shown to effectively reduce the incidence and severity of AMS, gradually ascending to high altitudes seems to be the best strategy for the prevention of altitude sickness [ 6 ].…”

“…Previous studies have indicated that some drugs may prevent AMS, but these prophylactic interventions may be accompanied with serious adverse effects [ 6 ]. Recently, clinical trials with healthy volunteers suggested that intravenous iron supplementation may protect against AMS.…”