Rapid ascents of Mt Everest: normobaric hypoxic preacclimatization.

Abstract

Acclimatization to high altitude is time consuming. An expedition to Mt Everest (8848m) requires roughly 8weeks. Therefore it seems very attractive to reach the summit within 3weeks from home, which is currently promised by some expedition tour operators. These rapid ascent expeditions are based on two main components, normobaric hypoxic training (NHT) prior to the expedition and the use of high flow supplemental oxygen (HFSO2). We attempted to assess the relative importance of these two elements. We evaluated the effect of NHT on the basis of the available information of these rapid ascent expeditions and our experiences made during an expedition to Manaslu (8163m) where we used NHT for preacclimatization. To evaluate the effect of an increased O2 flow rate we calculated its effect at various activity levels at altitudes of 8000m and above. So far rapid ascents to Mt Everest have been successful. The participants carried out 8weeks of NHT, reaching sleeping altitudes = 7100m and spent at least 300h in NH. At rest a flow rate of 2l O2/min is sufficient to keep the partial pressure of inspired oxygen (PIO2) close to 50mmHg even at the summit. For ativities of ~80% of the maximum rate of oxygen consumption (VO2max) at the summit 6l O2/min are required to maintain a PIO2 above 50mmHg. NHT for preacclimatization seems to be the decisive element of the offered rapid ascent expeditions. An increased O2 flow rate of 8l/min is not mandatory for climbing Mt Everest. Preacclimatization using normobaric hypoxica (NH) is far more important than the use of HFSO2. We think that NHT will be widely used in the future. The most effective regimen of preacclimatization in NH, the duration of each session and the optimal FIO2 are still unclear and require further study.