title: Pressure-volume characteristics of lungs of rats during pregnancy and postpartum.
abstract: Measurements of lung volumes in pregnant women show that the functional residual capacity and residual volume are reduced by 17-25% at late pregnancy. The present study was conducted to test the hypothesis that a decrease in FRC at pregnancy may result from an increase in retractive forces of the lung. The air and saline pressure-volume characteristics of excised lungs were studied in rats daily during pregnancy and the postpartum period. In comparison to non-pregnancy rats, the air PV measurements indicated that: (1) the retractive forces of the lungs were increased late in pregnancy resulting in reduction in both MLV (lung air volume at 40 cm H2O Ptp) and in V%10 (volume at 10/volume at 40 cm H2O Ptp X 100); (2) MLV was greater in lactating than in non-lactating and in non-pregnant rats. Lung saline volume was also greater in lactating than in non-lactating rats at early postpartum period. Lung phospholipids content was increased at late pregnancy and in lactating rats; (3) there was an increase in MLV and in V% immediately after delivery and 2-3 days after an abrupt cessation of lactation ("dried" rats). The minimal surface tension of lung lavages also decreased in these rats. A shift to that left of the air PV curve in "dried" rats suggest that under normal circumstances lung surface forces are not at their lowest.
mesh_terms: D000818:Animals; D005260:Female; D005652:Functional Residual Capacity; D008168:Lung / Q000502:physiology*; D008170:Lung Compliance; D008176:Lung Volume Measurements; D049590:Postpartum Period; D011247:Pregnancy; D011270:Pregnancy, Animal; D011663:Pulmonary Surfactants / Q000502:physiology; D051381:Rats
chemical_list: D011663:Pulmonary Surfactants