Effects of deep inspiration on bronchoconstriction in the rat

It is important to understand the mechanisms by which a deep inspiration (DI) affects bronchoconstriction in rodents so that their relevance as animal models of asthma can be assessed. We investigated the effect of DI on respiratory input impedance after methacholine inhalation in four groups of rats: a control group, a group receiving DI prior to challenge, and two groups receiving different degrees of DI after challenge. We measured respiratory input impedance for 15 min following a challenge. This provided time-courses approximating the resistance of the conducting airways and the impedance of the respiratory tissues. We found no significant difference in the peak changes in airway resistance comparing the control group and any of the DI groups following challenge. However, the peak increase in tissue impedance was reduced in the group receiving the largest DI after challenge. Our results thus suggest that the DIs that we administered were neither bronchodilatory nor bronchoprotective, but that they were able to reduce the amount of airway closure occurring following bronchoconstriction.