It is important to understand the mechanisms by which a deep inspiration (D
I) affects bronchoconstriction in rodents so that their relevance as animal
models of asthma can be assessed. We investigated the effect of DI on resp
iratory input impedance after methacholine inhalation in four groups of rat
s: 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-cours
es 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 res
ults thus suggest that the DIs that we administered were neither bronchodil
atory nor bronchoprotective, but that they were able to reduce the amount o
f airway closure occurring following bronchoconstriction. (C) 2001 Elsevier
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