[Modifications in the geometry of the alveolar capillaries and their role in the ventilation-perfusion ratio]

Abstract

Alveolar capillary bed corresponds to a continuous space delimited at each side by the thin portion of the air/blood barrier. The thick portion crosses this space and constitutes structures referred to as "pillars". While the capillary space appears more or less regular in inflated rat lungs, it resembles a labyrinth in collapsed lungs. Such a change is due to the folding of the thin portion of the barrier into the capillary space. Another mechanism involved in the folding of alveolo-capillary membrane is the contraction of alveolar interstitial cells. Experimentally, hypoxia seems to stimulate these cells and to produce folding of the air/blood barrier. We have shown that the alveolar hematocrite increases in rat lungs when the animals are exposed to 4% O2 for 20 min. This increase is probably due to the trapping of red blood cells in the capillary spaces as a result of folding of the air/blood barrier. It is concluded that the relationships between alveolar and capillary configuration is an important factor in the autoregulation of V/Q ratio. The decrease in alveolar perfusion in collapsed areas and during hypoxia is due to the interference of alveolo-capillary membrane folds with the corpuscular circulation.