Influence of hyperpnea on airway surface fluid volume and osmolarity in normal humans

To determine the effect of hyperpnea on the characteristics of periciliary liquid, we collected airway surface fluid (ASF) and measured its osmolarity in 11 normal people while they breathed dry, frigid air (−17 ± 1.2°C) at minute ventilations (V˙e) of 10, 40, and 80 l/min through a heat exchanger. The ASF was collected at the fifth tracheal ring by absorption onto filter paper pledgets inserted via fiber-optic bronchoscopy. Hyperpnea had no influence on the amount of ASF recovered (ASF volume at a V˙e of 10 l/min = 12.0 ± 2.0 μl; at 80 l/min = 8.8 ± 1.5 μl; P = 0.28) or its osmolarity (at a V˙e of 10, 40, and 80 l/min = 326 ± 15, 323 ± 11, and 337 ± 12 mosM, respectively; P = 0.65). These findings demonstrate that the tracheal mucosa of normal subjects does not desiccate during hyperpnea and that hypertonicity of the periciliary fluid does not develop even at high levels of ventilation.