Effect of nasal air temperature on lung function.

Inhalation of cold air is known to induce intrapulmonary airway obstruction in sensitive asthmatic patients and this is a condition often ascribed to heat and water losses from the airway mucosa ( 1-6). However, the pathophysiological mechanism explaining why airway cooling and exercise cause broncho-obstruction is not yet clear. The fact that anticholinergic drugs suppress exercise-induced asthma may indicate a reflex through the vagal nerve, although blockade of this nerve does not completely prevent bronchoobstruction induced by exercise in asthmatic patients (7-1 1). The fact that sodium cromoglycate prevents the development of exercise-induced asthma (9, 12-1s) and that elevated levels of histamine are present in exercise-induced asthma (1 1 , 16-18) indicate that mediators may be involved. The importance of the latter is uncertain, since antihistamines have a poor preventive effect in exercise-induced asthma (19). Changes in osmolarity of the airway lining may also be an important factor ( 2 e 2 2 ) . Furthermore, asthmatic patients react with broncho-obstruction when challenged with hypoand hyperosmolar solutions ( 2 3 , 24) (Fig. 1).