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The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205
Deep inspirations (DIs) have been shown to have both
bronchoprotective and bronchodilator effects in healthy subjects;
however, the bronchodilator effects of a DI appear to be impaired in
asthmatic compared with healthy subjects. Because the ability to
generate high transpulmonary pressures at total lung capacity depends
on both the lung properties and voluntary effort, we wondered how the
response of airways to DI might be altered if the maneuver were done
with less than maximal inflation. The present work was undertaken to
examine the effects of varying the magnitude of lung inflation during
the DI maneuver on subsequent airway caliber. In five anesthetized and
ventilated dogs during methacholine infusion, changes in airway size
after DIs of increasing magnitude were measured over the subsequent
5-min period using high-resolution computed tomography. Results show
that the magnitude of lung inflation is extremely important, leading to
a qualitative change in the airway response. A large DI (45 cmH2O airway pressure) caused subsequent airway dilation,
whereas smaller DIs (
35 cmH2O) caused bronchoconstriction. The precise mechanism underlying these
observations is uncertain, but it seems to be related to an interaction
between intrinsic properties of the contracted airway smooth muscle and the response to mild stretch.
asthma; bronchoconstriction; high-resolution computed tomography; lung inflation; smooth muscle
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