[Sports and extreme conditions. Cardiovascular incidence in long term exertion and extreme temperatures (heat, cold)].
During ultra-endurance exercise, both increase in body temperature and dehydration due to sweat losses, lead to a decrease in central blood volume. The heart rate drift allows maintaining appropriate cardiac output, in order to satisfy both muscle perfusion and heat transfer requirements by increasing skin blood flow. The resulting dehydration can impair thermal regulation and increase the risks of serious accidents as heat stroke. Endurance events, lasting more than 8 hours, result in large sweat sodium chloride losses. Thus, ingestion of large amounts of water with poor salt intake can induce symptomatic hyponatremia (plasma sodium < 130 mEq/L) which is also a serious accident. Heat environment increases the thermal constraint and when the air humidity is high, evaporation of sweat is compromise. Thus, thermal stress becomes uncompensable which increases the risk of cardiovascular collapse. Cold exposure induces physiological responses to maintain internal temperature by both limiting thermal losses and increasing metabolic heat production. Cold can induce accidental hypothermia and local frost-bites; moreover, it increases the risk of arrhythmia during exercise. Some guidelines (cardiovascular fitness, water and electrolyte intakes, protective clothing) are given for each extreme condition.
Melin
B
B
Unité de bioénergétique et environment, Centre de recherches du service de santé des armées Emile-Pardé 24, avenue des maquis du Grésivaudan BP 87 38702 La Tronche. brunomelin@compuserve.com
Savourey
G
G
D002318:Cardiovascular Diseases / Q000209:etiology* / Q000517:prevention & control; D002320:Cardiovascular Physiological Phenomena; D003080:Cold Temperature / Q000009:adverse effects*; D005334:Fever / Q000209:etiology* / Q000517:prevention & control; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D007035:Hypothermia / Q000209:etiology* / Q000517:prevention & control; D015994:Incidence; D010807:Physical Endurance; D011322:Primary Prevention / Q000379:methods; D012307:Risk Factors; D013177:Sports; D013178:Sports Medicine / Q000379:methods; D013997:Time Factors; D014883:Water-Electrolyte Imbalance / Q000209:etiology* / Q000517:prevention & control
Sports et conditions extrêmes. Incidence cardiovasculaire des efforts de longue durée et des températures extrêmes (chaleur, froid).