Cold and the airways.

Physiological and pathological respiratory responses are triggered by various conditions of exposure to cold climates. Beside airway smooth muscle, both the pulmonary and the tracheobronchial vasculatures are major effectors of respiratory responses to cold. General exposure to cold causes pulmonary vasoconstriction known as "Raynaud's phenomenon of the lung" in subjects with primary Raynaud syndrome and favors acute pulmonary oedema in subjects with congestive heart failure. In healthy subjects acute hyperventilation of very cold air has led to acute respiratory failure closely similar to hypoxic pulmonary oedema. In outdoor exercising people years long repetition of hyperventilation of subfreezing air causes "eskimo lung" made of obstructive lung disease and increased wall thickness of pulmonary arteries. At a lesser degree hyperventilation of dry air cools the central airways and triggers subclinical bronchial obstruction in healthy subjects. In asthmatic subjects hyperventilation of dry air causes asthma attacks. Results of recent animal and human experiments point to a key role of mucosal vessels in thermal balance of the airways. Simultaneously, there is increasing evidence that hyperventilation-induced asthma is triggered by a thermal stimulus.