Effect of liquid inflation on the viscoelastic behavior of the lungs in developing piglets.
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.
Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut 06510.
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La Rocca
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Pérez Fontán
D000388:Air; D000818:Animals; D000831:Animals, Newborn; D004548:Elasticity; D008168:Lung / Q000254:growth & development / Q000502:physiology*; D008170:Lung Compliance; D012965:Sodium Chloride; D013314:Stress, Mechanical; D013552:Swine; D014783:Viscosity
D012965:Sodium Chloride