RBC oxygen uptake and the effects of diffusion and perfusion

Sharpen your knowledge about alveolar diffusion with this article on factors that affect red blood cell oxygen uptake.
Last update29th Jan 2021

The partial pressure of oxygen (oxygen tension) of mixed venous blood is 40 mmHg. It rises to the alveolar oxygen tension of 100 mmHg in about 0.25 seconds after entering the pulmonary capillaries.

Figure 1. The partial pressure of oxygen of mixed venous blood (40 mmHg) rises to the partial alveolar oxygen tension (100 mmHg) after entering the pulmonary capillaries.

With mild or moderate diffusion impairment—for example, in diseases producing thickening of the alveolar-capillary membrane—equilibration of capillary blood oxygen tension and alveolar gas is essentially complete by the time the aliquot of blood transits through the capillary. However, with significant diffusion impairment, end-capillary blood oxygen tension may be significantly lower than alveolar oxygen tension, creating a widened alveolar-arterial oxygen gradient.

Figure 2. Graphical representation of the equilibration of capillary blood oxygen tension and alveolar gas across time. In diseases that produce thickening of the alveolar-capillary membrane, the equilibration of capillary blood oxygen tension and alveolar gas takes longer to complete. Diseases with significant diffusion impairment can have end-capillary blood oxygen tension lower than alveolar oxygen tension.

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The effect of alveolar hypoxia on arterial oxygen tension is accentuated during exercise, when the transit time of red blood cells in the pulmonary capillaries is shortened.

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Recommended reading

  • Grippi, MA. 1995. “Gas exchange in the lung”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 137–149)
  • Grippi, MA. 1995. “Clinical presentations: gas exchange and transport”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 171–176)
  • Grippi, MA and Tino, G. 2015. “Pulmonary function testing”. In: Fishman's Pulmonary Diseases and Disorders, edited by MA, Grippi (editor-in-chief), JA, Elias, JA, Fishman, RM, Kotloff, AI, Pack, RM, Senior (editors). 5th edition. New York: McGraw-Hill Education. (Grippi and Tino 2015, 502–536)
  • Tino, G and Grippi, MA. 1995. “Gas transport to and from peripheral tissues”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Tino and Grippi 1995, 151–170)
  • Wagner, PD. 2015. The physiologic basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases. Eur Respir J45: 227–243. PMID: 25323225

About the author

Michael A. Grippi, MD
Vice Chairman, Department of Medicine | Pulmonary, Allergy, and Critical Care Division, Perelman School of Medicine, University of Pennsylvania, USA.
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