Pulmonary transit time and diffusing capacity in mammals

S. L. Lindstedt

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


Allometry is used as a tool to explain the apparent mismatch of oxygen consumption and diffusing capacity in the mammalian lung. By combining equations for pulmonary capillary volume and cardiac output, it is apparent that erythrocytes transit time through the lung must scale disproportionately to body mass. This inequality is a consequence of physical and mechanical properties setting optimal cardiac and respiratory frequencies. Because of much shorter transit times, the mean alveolar-capillary oxygen pressure difference increases as body size decreases. The time course of oxygen binding to hemoglobin may limit maximum oxygen consumption in the smallest mammals. To assure carbon dioxide diffusion equilibrium, levels of carbonic anhydrase are much higher in small than in large mammals. Because of the differences in transit time, the pulmonary diffusing capacity must scale linearly to body mass to assure adequate oxygen delivery in all mammals.

Original languageEnglish (US)
Pages (from-to)R384-R388
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number3
StatePublished - 1984

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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