Dry gas hyperpnea changes airway reactivity and ion content of rabbit tracheal wall

Dry air hyperventilation provokes airway narrowing in asthmatics. The mechanism is thought to involve the release of inflammatory mediators in response to airway osmolarity. The response to inhaled histamine on lung mechanics and the ion content of the airway subepithelial connective tissue after dry gas hyperventilation was investigated in rabbits. Resistance increased more after histamine given after hyperventilation with dry gas compared to humid gas (P < 0.05). Compliance decreased after histamine for both dry and humid gas hyperventilation. The Na, Cl and K content was decreased in the tissue at 4 min (P < 0.001) and nearly returned to resting content at 8 min of hyperventilation with dry gas. The results suggest that dehydration occurred and was followed by oedema formation in the tracheal wall. Thus, the effects of inhaled histamine on airway resistance was amplified. The mechanism involved may be part of the normal defence of the airway to protect against desiccation during hyperventilation with dry air. This response may be exaggerated in asthmatics.