Journal of Applied Physiology, Vol 48, Issue 1 29-33, Copyright © 1980 by American Physiological Society
Forces involved in lobar atelectasis in intact dogs
G. T. Ford, C. A. Bradley and N. R. Anthonisen
When an excised lung lobe undergoes atelectasis, its shape differs from
that observed when lobar atelectasis occurs in an intact animal: the chest
wall deforms the collapsing lobe. In eight anesthetized dogs in the left
lateral position we measured lung volume and transpulmonary pressure during
the development of atelectasis. We then induced atelectasis of the left
lower lobe with the rest of the lung maintained at FRC and measured lobar
volume and "translobar" (lobar minus esophageal) pressure. Lung and lobar
volumes were measured by prebreathing the animal with 88% O2-12% N2,
occluding the airway and observing the increase in lung or lobar N2
concentration. When the left lower lobe alone collapsed, translobar
pressures were more negative than transpulmonary pressure at the same
relative volume when the whole lung collapsed. This pressure difference,
which represents the deforming force applied to the lobe minus the pressure
costs of deformation, averaged 3 cmH2O at 50% FRC. Infusion of 25 ml of
normal saline into the pleural space sharply reduced the difference
pulmonary pressure during lung collapse: this difference was abolished at
80% FRC and halved at 50% FRC. The large effect of the small volume of
fluid suggested that deforming forces were largely generated in relatively
local areas, such as regions of the chest wall with sharp angulation.
