Which scenario best describes the effect of humidity on exercise-induced bronchospasm?

• A. Bronchospasm is facilitated by exercise in a humid environment, compared with a dry environment.
• B. Bronchospasm is facilitated by exercise in a warm environment, compared with a cold environment.
• C. Bronchospasm is blunted when exercising in a humid environment, compared with a dry environment.
• D. Bronchospasm is blunted when exercising in a cold environment, compared with a warm environment.

Answer: (C)

When you breathe in during exercise, the airways warm and humidify the air, but the rapid, deep breathing can still dry and cool the airway surfaces. That drying increases mucosal osmolarity and triggers release of substances that cause the airway muscles to tighten, leading to bronchospasm. Humid air helps keep the airway surfaces hydrated, reducing this stimulus and thus lessening the bronchoconstriction. So exercising in a humid environment tends to blunt exercise-induced bronchospasm compared with a dry environment. The other ideas focus on warmth or coldness rather than humidity, which doesn’t describe the protective effect humidity has on the airways.