Morphometric estimation of pulmonary diffusion capacity. VI. Effect of varying positive pressure inflation of air spaces

Ewald R. Weibel, Peter Untersee, Joan Gil, Martin Zulauf

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The changes in lung volume related to inflation and deflation cause a hysteretic variation of the free alveolar surface area. It is examined in this study by how much this influences pulmonary diffusion capacity. Lungs fixed by vascular perfusion at five points of the pressure-volume diagram were studied by electron microscopy using stereological methods. The alveolar surface was reduced at lower inflation levels by gradual folding of the septa beneath the surface lining layer. Part of the capillary network becomes shifted to deeper regions of the septum. Most of the tissue barrier exposed to the free surface consists of the thinnest barrier portions, the thicker parts being dislocated into the depth of the septum; this reduces the effective mean barrier thickness as compared to that measured on completely unfolded lungs. The capillary volume shows a pattern of reversed hysteresis; this can be explained by the hysteretic change in the free alveolar surface and the use of a constant capillary pressure. It is concluded that the variations in the level of lung inflation lead to a reduction in the available diffusion capacity by as much as 50 to 75 percent as compared to the values obtained on completely unfolded lungs. This may explain part of the differences between physiological and morphometric estimates of dl.

Original languageEnglish
Pages (from-to)285-308
Number of pages24
JournalRespiration Physiology
Issue number3
StatePublished - Sep 1973
Externally publishedYes


  • Alveolo-capillary membrane
  • Capillary blood
  • Diffusion capacity
  • Electron microscopy of lung
  • Lung inflation
  • Morphometry
  • Pulmonary hysteresis
  • Surface lining layer


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