Hyperventilation with dry air increases airway surface fluid osmolality incanine peripheral airways

Hyperventilation-induced bronchoconstriction (HIB) is a component of exerci se-induced asthma (EIA) believed to result from the penetration of uncondit ioned air into the lung periphery. We used a canine model of EIA to examine the effect of hyperventilation on airway surface fluid (ASF) volume and os molality, and to determine if the observed kinetics support the hypothesis that hyperventilation-induced changes in ASF osmolality initiate bronchocon striction. Exposure of sublobar airways to dry air at baseline insufflation resulted in stable measurements of ASF volume, ASF osmolality, and periphe ral airway resistance (Rp). Baseline insufflation of warm humidified air in creased ASF volume, but did not alter ASF osmolality. Hyperventilation chal lenge with warm humidified air (WAC) increased R-p and ASF volume, but decr eased ASF osmolality. Dry air challenge (DAC) increased R-p, ASF volume, an d ASF osmolality. ASF osmolality during DAC was markedly higher when compar ed with posthyperventilation values. Post-DAC changes in (Delta) ASF volume and osmolality were poorly correlated with the development of HIB. In cont rast to Delta ASF after DAC, a ASF osmolality during DAC was strongly corre lated with HIB, and tended to be inversely related to Delta ASF volume. The se observations are consistent with the hypothesis that changes in airway o smolality during hyperventilation initiate peripheral airway constriction.