Flow and protein concentration of lymph from lungs of lambs developing hyaline membrane disease.

Wide tissue septa and dilated lymphatics can be seen in histological sections from the lungs of infants dying from hyaline membrane disease (Wade-Evans, 1962; Balis, Delivoria, and Conen, 1966). These might be produced either by the excessive transfer of liquid from the plasma to the lung interstices, or by the defective clearance of the liquid which normally fills the potential airspaces of the fetal lung. Indeed, both these processes may occur. Liquid and proteins are normally cleared from interstitial spaces through lymphatics, and in the lamb at the onset of breathing there is a large increase in pulmonary lymph flow, which is responsible for the removal of much of the fetal lung liquid (Boston et al., 1965; Humphreys et al., 1967). In the experiments of Humphreys et al. (1967) the increase in pulmonary lymph flow at the start of breathing was smaller in premature lambs, and the decrease in their lung weight after 2 hours of ventilation was less than in mature animals. Unasphyxiated immature lambs delivered at about 125-130 days of gestation (term is at approximately 147 days) develop a clinical and histological picture which seems indistinguishable from that seen in hyaline membrane disease in the human infant (Reynolds et al., 1965a). The present paper describes the histological appearances of the lungs of immature and mature lambs in which lymph flow measurements were made, with special reference to atelectasis, hyaline membrane formation, and the appearance of the tissue septa and lymphatics. The histology and lymph flow measurements are related to the surface tension characteristics of lung extracts.