THE RESPIRATORY SYSTEM IN A COLD ENVIRONMENT

Acute or chronic cold exposure elicits several effects on the respirat ory system. Pulmonary mechanics are compromised by bronchoconstriction , airway congestion, secretions and decreased mucociliary clearance. T hese responses are active in cold- or exercise-induced asthma, and are possibly responsible for decreased immune function and protection aga inst airborne pollutants. The primary ventilatory effect of cord air i s to decrease baseline Ventilation and respiratory chemosensitivity. A lthough these responses provide significant protection against heat lo ss in many animals, the effect in humans is minimal. Cold exposure als o elicits an increase in pulmonary vascular resistance. This stimulus is synergistic with hypoxia and may mediate pulmonary hypertension and edema at altitude. Chronic exposure to cold environments results in m orphological changes such as increased numbers of goblet cells and muc ous glands, hypertrophy of airway muscular fascicles and increased mus cle layers of terminal arteries and arterioles. These latter two facto rs may play a role in the symptoms of chronic obstructive pulmonary di sease and bronchitis, high altitude pulmonary hypertension and edema, and right heart hypertrophy.