Rapid alveolar liquid removal by a novel convective mechanism

Abstract

Although alveoli clear liquid by active transport, the presence of surface-active material on the alveolar surface suggests that convective mechanisms for rapid liquid removal may exist. To determine such mechanisms, we held the isolated blood-perfused rat lung at a constant alveolar pressure (PA). Under videomicroscopy, we micropunctured a single alveolus to infuse saline or Ringer solution in approximately 10 adjacent alveoli. Infused alveoli were lost from view. However, as the infused liquid cleared, the alveoli reappeared and their diameters could be quantified. Hence the time-dependent determination of alveolar diameter provided a means for quantifying the time to complete liquid removal (C(t)) in single alveoli. All determinations were obtained at an PA of 5 cmH(2)O. C(t), which related inversely to alveolar diameter, averaged 4.5 s in alveoli with the fastest liquid removal. Injections of dye-stained liquid revealed that the liquid flowed from the injected alveoli to adjacent air-filled alveoli. Lung hyperinflations instituted by cycling PA between 5 and 15 cmH(2)O decreased C(t) by 50%. Chelation of intracellular Ca(2+) prolonged C(t) and abolished the inflation-induced enhancement of liquid removal. We conclude that when liquid is injected in a few alveoli, it rapidly flows to adjacent air-filled alveoli. The removal mechanisms are dependent on alveolar size, inflation, and intracellular Ca(2+). We speculate that removal of liquid from the alveolar surface is determined by the curvature and surface-active properties of the air-liquid interface.

Endothelial connexin43 mediates acid-induced increases in pulmonary microvascular permeability

“…By spatially limiting the instillation, it was possible to 1) ensure that the responses were microvessel specific and 2) simultaneously visualize the instilled and free regions within the field of view of our microscope. Although liquid-filled alveoli were clearly identifiable under bright-field illumination, as previously reported (27), RDx70 fluorescence allowed identifying even partially filled . The rapid phase rate was calculated as the change in fluorescence over 3 min, beginning 1 min after the start of the fluorescence increase.…”

“…At the end of the instillation, the micropipette was withdrawn, to allow recovery of both the micropunctured and the surrounding alveoli (Fig. 1C), as previously reported (27). The spatial spread of acid was evident only during instillation of the acid.…”

Disruption of staphylococcal aggregation protects against lethal lung injury

“…By way of the micropipettes, we microinstilled the micropunctured alveoli with fluorophores, reagents, solutions, and antibodies, resulting in their spread from the micropunctured alveolus to at least 20 neighboring alveoli within local lung acini, as evident by transient loss of optical discrimination between alveolar walls and air spaces. Return of optical discrimination occurred within seconds of each microinstillation, indicating free fluid rapidly drained from the alveolar lumens (61). We imaged the microinstilled alveolar fields but excluded the micropunctured alveoli from the region imaged.…”

F-actin scaffold stabilizes lamellar bodies during surfactant secretion

“…To load the alveolar epithelium with fluorescent dyes, we microinfused the dyes through glass micropipettes inserted in the alveolar space (1,11,24). Each microinfusion filled 8 -10 alveoli, but then quickly drained leaving the alveolar air space free of the injected fluid (30). We carried out studies in alveoli that were not directly micropunctured.…”