Journal of Applied Physiology, Vol 75, Issue 4 1536-1544, Copyright © 1993 by American Physiological Society
Effect of lung lavage on the stress relaxation of the respiratory system
J. J. Perez Fontan
Department of Pediatrics, Washington University School of Medicine, Saint Louis, Missouri 63110.
To test the hypothesis that lowering the concentrations of surfactant
molecules at the gas-liquid interface increases viscoelastic dissipation in
the lungs, the amplitude and time course of stress relaxation were
quantified before and after lavage of the lungs with warm saline in five
newborn and five 8-wk-old anesthetized piglets. Stress relaxation was
separated from other dissipative pressure losses by fitting the pressure
decays that follow airway occlusions performed during a period of constant
inspiratory flow to a double-exponential regression. The amplitude of
stress relaxation (defined by the term of the regression with the longest
time constant) related linearly to the changes in respiratory system volume
and elastic recoil preceding the occlusions both before and after the
lavage. Lung lavage increased the slope of both relationships without
altering the time course of the relaxations. In addition to being
consistent with the proposed hypothesis, these results suggest that
viscoelastic pressure losses remain linked to the elastic stresses
generated during lung inflation, as proposed by Fredberg and Stamenovic's
structural dumping theory (J. Appl. Physiol. 67: 2408-2419, 1989).
