The role of climatic conditions and histamine release in exercise-induced bronchoconstriction

We examined the role of climatic conditions on exercise induced asthma in patients in the tropics. Ten asthmatic patients exercised on a cycle ergometer achieving similar maximal heart rates, oxygen consumption, work load, and minute ventilation on three occasions, breathing warm humid air, cool drier air and cold dry air. Blood for plasma histamine was collected before and after exercise breathing cold air. The exercise-induced bronchoconstriction (EIB) was least in warm air, maximal in cold air and intermediate in cool air. Post exercise venous histamine was raised in only 2 out of 7 patients. We conclude that temperature and humidity have a direct role in EIB and that mediator release is probably the result rather than the cause of EIB.