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Departments of 1 Medicine and 3 Pathology and Laboratory Medicine and 2 McDonald Research Laboratories, iCapture Center, St. Paul's Hospital, Providence Health Care, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
The physically dynamic environment of
the lung constantly modulates the mechanical properties of airway
smooth muscle. In vitro experiments have shown that
contractility of the muscle is compromised by oscillatory strains,
perhaps through disruption of cross-bridge interaction and organization
of the contractile filaments. To understand the mechanism by which
oscillation affects contractility, functional changes of the muscle in
terms of force-velocity relationship were assessed before and after
imposition of length oscillation in both relaxed and activated states.
The oscillation protocol was designed to reduce isometric force by
15-20%, followed by measurement of force-velocity properties.
Maximal velocity and power changed by +8 and 
14%, respectively,
after oscillation applied in the relaxed state and changed by 15 and
25%, respectively, after oscillation applied during contraction. A
simple model of reduced activation could not account for the results;
neither could the results be explained satisfactorily by the current
cross-bridge theory of contraction. The results, however, could be
explained if the possibility of reorganization of the contractile
filaments due to oscillatory strains was considered.
airway smooth muscle; mechanics; power output; internal load; contractile units
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