Journal of Applied Physiology, Vol 77, Issue 4 1653-1658, Copyright © 1994 by American Physiological Society
Effect of liquid inflation on the viscoelastic behavior of the lungs in developing piglets
J. La Rocca and J. J. Perez Fontan
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
Viscoelastic dissipation through stress relaxation decreases during the
first weeks after birth in the piglet's lungs (J. Appl. Physiol. 73:
1297-1309, 1992). To characterize the mechanism of this decrease, we
compared the stress relaxation undergone by the lungs of six newborn and
six 9-wk-old piglets when the airway opening was occluded in the course of
air and saline inflations. The amplitude of stress relaxation, determined
from the mono-exponential decay ultimately adopted by the transpulmonary
pressure during the occlusions, related linearly to the increases in lung
elastic recoil preceding the occlusions. The slope of this relationship was
greater in the newborn than in the 9-wk-old piglets during air inflations
and similar at the two ages during saline inflations. Both the ratio of
stress relaxation to elastic recoil and the time constant of the
relaxations were similar during air and saline inflations and were
independent of inflation rate and lung volume at the start of the
inflations. These findings indicate that the postnatal decrease in stress
relaxation is caused primarily by developmental changes in the geometry of
the gas-liquid interface. They are also consistent with the notion that the
viscoelastic stresses generated by the gas liquid interface and lung tissue
are well matched for a given elastic recoil.
