Red cell distribution and the recruitment of pulmonary diffusing capacity

Connie C W Hsia, Robert L. Johnson, Dipen Shah

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


The distribution of red blood cells in alveolar capillaries is typically nonuniform, as shown by intravital microscopy and in alveolar tissue fixed in situ. To determine the effects of red cell distribution on pulmonary diffusive gas transport, we computed the uptake of CO across a two- dimensional geometric capillary model containing a variable number of red blood cells. Red blood cells are spaced uniformly, randomly, or clustered without overlap within the capillary. Total CO diffusing capacity (DL(CO)) and membrane diffusing capacity (Dm(CO)) are calculated by a finite-element method. Results show that distribution of red blood cells at a fixed hematocrit greatly affects capillary CO uptake. At any given average capillary red cell density, the uniform distribution of red blood cells yields the highest Dm(CO) and DL(CO), whereas the clustered distribution yields the lowest values. Random nonuniform distribution of red blood cells within a single capillary segment reduces diffusive CO uptake by up to 30%. Nonuniform distribution of red blood cells among separate capillary segments can reduce diffusive CO uptake by >50%. This analysis demonstrates that pulmonary microvascular recruitment for gas exchange does not depend solely on the number of patent capillaries or the hematocrit; simple redistribution of red blood cells within capillaries can potentially account for 50% of the observed physiological recruitment of DL(CO) from rest to exercise.

Original languageEnglish (US)
Pages (from-to)1460-1467
Number of pages8
JournalJournal of applied physiology
Issue number5
StatePublished - May 1999


  • Capillary model
  • Finite-element analysis
  • Membrane diffusing capacity
  • Pulmonary diffusing capacity

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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