Sport in Extreme Environments: Cardiovascular Issues

Abstract

Exposure to extreme environments has become increasingly attractive. The remotest places on earth like the poles, the high mountain peaks, the hot deserts, or the deep sea are particularly fascinating. Although the most extreme environments remain rather reserved to a few extraordinary people, improved access and infrastructure nowadays allow millions of visitors to pursue recreational outdoor activities in extremely cold or hot regions, in hypobaric hypoxia (high altitudes) or hyperbaria (diving). Humans are homeotherms, meaning that their core temperature has to be held constant within a relatively narrow range (35.0–37.5 °C). Exposure to cold air or cold water is associated with the risk of hypothermia (core temperature below 35 °C), which is especially pronounced in cold water. In contrast, heat exposure may provoke the risk of hyperthermia (core temperature above 37.5 °C), which is especially distinct during exercise. With increasing altitude (hypobaric hypoxia) aerobic capacity (maximal oxygen uptake, VO2max) declines by about 1.5–3.5% every 300 m of altitude gain. On the other hand, when exercising at depth (diving, hyperbaria) oxygen supply needs to be maintained by artificial means. Without breathing gas supply, exposures are limited to the individual breath-hold time. Due to the greater health risk when exercising under extreme conditions, pre-exposure medical assessment of exercise performance and cardiorespiratory functioning are of utmost importance. Both exercise training to achieve an appropriate cardiovascular fitness and habituation/acclimatization to the specific environmental conditions are important preventative measures for both athletes and patients.