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Among the forces that may contribute to the first inflation of the lungs after birth, those developed through changes in the pulmonary circulatory system have been assigned primary importance by Jaykka (1), Bonham Carter (2) and Adams, Karlberg and Lind (3). Possibly the earliest basis for this view was provided during the last century by von Basch (4) who showed in animals and also in experimental models that pulmonary vascular congestion, presumably at the capillary level, tends to increase the volume of gas in the lungs. Recently, it was demonstrated in excised 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 congestion is sufficiently large to cause air to enter the lung. The object of this study was to test this second 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. Measurements 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. METHODS Excised lungs from four adult cats, one adult dog, five fetal puppies and two stillborn infants were used. The animal lungs were made gas-free by a modification of the technique of Coryllos and Birnbaum (7). The cats were anesthetized with 30 mg. per Kg. of pentobarbital (Nem-butal®) 1 injected intraperitoneally; the dogs were given the same dose intravenously. Ninety-nine plus per cent of oxygen was used to ventilate the lungs through a tracheal cannula for about 15 minutes, after which the chest was opened and the trachea was occluded to permit absorption of the gas by the pulmonary circulation. Early in the period of gas-freeing 375 mg. of mepe-sulfate2 (an anticoagulant), diluted with saline, was injected into the left ventricle. The heart and lungs were excised together. Cannulae were …

the journal of clinical investigation/the journal of clinical investigation

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