ABSTRACT
Presently, there are two main theories to explain the relationship between physical activity and EIA. Firstly, the theory of airway cooling due to respiratory heat loss with rewarming by secondary hyperaemia and pulmonary vasodilatation will be considered.11 As the inspiratory air is rapidly saturated with water vapour during breathing, the temperature of the inspiratory air also increases. Through thermal mapping McFadden and coworkers demonstrated that the temperature increased from 32.0 0.05°C in the upper trachea to 35.5 0.3°C in the subsegmental bronchi during quiet breathing (ventilation 15 l/min) of room air (26.7 0.5°C).12 During increasing ventilation the temperature fell, and with a maximum ventilation of 100-120 l/min the temperature in the upper trachea was 29.2 0.5°C, and 33.9 0.8°C in the subsegmental bronchi. During maximum ventilation with frigid air (18.6 1.2°C) the upper tracheal temperature was 20.5 0.6°C and the subsegmental bronchial temperature was
Furthermore, owing to pulmonary vasoconstriction induced by the cold air, a secondary reactive hyperaemia may occur, with resulting oedema and airways narrowing.11
