[Overview of the most important (patho)physiological mechanisms of high-altitude acclimatization in healthy individuals].

More and more people are spending time at high altitudes, either recreationally or permanently. As altitude increases, the partial pressure of inspired oxygen decreases, leading to hypobaric hypoxia and triggering a wide range of physiological adaptations. This article discusses the most relevant (patho)physiological acclimatization effects at high altitudes in healthy subjects. Hypobaric hypoxia primarily affects respiration, circulation, blood, as well as sleep and brain function. Respiration responds immediately with increased ventilation (hypoxic ventilatory response), reducing CO₂ levels and causing respiratory alkalosis, which is later compensated renally. Above approximately 2500 m, periodic breathing often occurs, disrupting sleep. Cardiac output initially rises due to an increased heart rate but decreases later as stroke volume declines. Plasma volume contracts rapidly, raising hematocrit and increasing blood viscosity. In the long term, erythropoietin stimulates red blood cell production, enhancing oxygen transport capacity. Physical performance begins to decline linearly from around 1500 m, and maximum oxygen uptake remains limited despite acclimatization.