High-altitude medicine: important for trekkers and mountaineers, essential for progress in medicine.

It is a pleasure to dedicate an issue of Progress in Cardiovascular Diseases to high-altitude medicine, and we gratefully thank the editors for giving us this opportunity. The readers will discover that the frontiers of highaltitude medicine are almost infinite and often extend to low altitude. Why is this so? Progress in medicine is intimately linked with the understanding of underlying mechanisms of disease. At high altitude, the ambient hypoxia triggers a series of physiologic responses that affect principally the respiratory, cardiovascular, neuroendocrine, and renal systems with the goal of maintaining adequate cellular oxygenation. At low altitude, the same systems may be activated with the same goal. The trigger, however, is not ambient hypoxia but hypoxemia that is the consequence of an organ insufficiency, usually the heart or the lung. Therefore, the ultimate goal of most high-altitude researchers is not only to understand physiologic (mal)adaptation to hypoxia for the benefit of the millions exposing themselves to high altitude, but to think beyond that, imagining how the knowledge gained from field research at high altitude may be applied to the much larger number of patients with hypoxia/ hypoxemia-associated diseases. A recent example of research from our own group may illustrate this state of mind. As detailed elsewhere in this issue, high-altitude pulmonary edema (HAPE) offers a unique model to study underlying mechanisms of pulmonary edema in humans (see p 485 by Scherrer et al).