[Alveolar recruitment under high-pressure transpulmonary inflation. An experimental morphometric study]

We describe an experimental study in which morphometric techniques are used to question traditional conceptions about the behavior of the alveolus under changes in pressure. An increase in inflation pressure in the lung results in alveolar recruitment (an increase in distal air spaces) due to stretching of its walls. To test this hypothesis, the lungs of rats were filled to 25 to 35 cm water pressure. Lungs filled to a higher pressure were expected to present a decrease in alveolar size along with thinning of its walls, and an increase of internal perimeter of the alveolus with no change in amount of tissue. Morphometric data were processed by computer and results were analyzed by statistical tests. The lungs of 10 Wistar rats were examined under light microscope. The following variables were recorded: mean linear intersection (Lm), alveolar cord, wall thickness, internal alveolar perimeter and tissue percentage. Lower Lm in lungs filled to 35 cm water pressure allows us to consider that the number of alveoli increased; lower Lm and alveolar cord indicate that alveolar size is smaller; alveolar wall thickness decreased; internal alveolar perimeter increased. All these differences were statistically significant (p < 0.001), tissue percentage being the only variable that did not change significantly. All results lead us to consider that an increase in lung inflation pressure leads to alveolar recruitment and stretching of its walls.