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1 Department of Medicine, University of Texas Southwestern Medical School, Dallas, Texas 75390-9034; and 2 Departments of Medicine and Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 99195
Pneumonectomy (PNX)
leads to chronic asymmetric ventilatory loading of respiratory muscles
(RM). We measured RM energy requirements during exercise from RM blood
flow (
) using a fluorescent microsphere technique in dogs that
had undergone right PNX as adults (adult R-PNX) or as puppies (puppy
R-PNX), compared with dogs subjected to right thoracotomy without PNX
as puppies (Sham) and to left PNX as adults (adult L-PNX). Ventilatory
work (
) was measured during exercise. RM weight was determined
post mortem. After adult and puppy R-PNX, the right hemidiaphragm
becomes grossly distorted, but
and right costal muscle mass
increased only after adult R-PNX. After adult L-PNX, the diaphragm was
undistorted;
and left hemidiaphragm RM
were
elevated, but muscle mass did not increase. Mass of parasternal muscle
did not increase after adult R-PNX, despite increased
. Thus
muscle mass increased only in response to the combination of chronic
stretch and dynamic loading. There was a dorsal-to-ventral gradient of
increasing
within the diaphragm, but the distribution was
unaffected by anatomic distortion, hypertrophy, or workload, suggesting
a fixed pattern of neural activation. The diaphragm and parasternals
were the primary muscles compensating for the asymmetric loading from PNX.
pneumonectomy; diaphragm; microspheres; work of breathing; dog
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