The inflationary force produced by pulmonary vascular distention in excised lungs. The possible relation of this force to that needed to inflate the lungs at birth

Among the forces that may contribute to the first inflation of the lungs after birth, those de-veloped through changes in the pulmonary circu-latory system have been assigned primary impor-tance by Jaykka (1), Bonham Carter (2) and Adams, Karlberg and Lind (3). Possibly the ear-liest basis for this view was provided during the last century by von Basch (4) who showed in ani-mals and also in experimental models that pulmo-nary vascular congestion, presumably at the capil-lary level, tends to increase the volume of gas in the lungs. Recently, it was demonstrated in ex-cised cats ' lungs that the expansile force resulting from vascular congestion is greatest when the lungs are collapsed (5). Together, these findings might be taken as evidence underscoring the role of vas-cular distention in expanding the lungs at birth. Before this view is accepted, however, two facts must be established. One is that the increase in pulmonary blood flow precedes the first breath. This is contrary to the findings of Dawes in fetal lambs that pulmonary blood flow is increased only after inflation has occurred (6). The other is that the force developed through vascular filling or con-gestion is sufficiently large to cause air to enter the lung. The object of this study was to test this sec-ond possibility. Experiments were carried out to compare the distending forces produced by a wide range of pulmonary vascular pressures with the force required to inflate the lungs. Measure-ments were made on excised lungs of adult cats and dogs that were freed of gas to simulate their condition at birth, and on lungs of puppies and newborn infants that had not breathed