Asthma and ARDS as examples of altered ventilation-perfusion ratios

In this Medmastery article, learn about altered lung ventilation-perfusion ratios in patients with asthma and ARDS.
Last update4th Dec 2020

Range of ventilation-perfusion ratios in normal lungs

Using a technique called the multiple inert gas technique, a range of ventilation-perfusion ratio values has been demonstrated in normal lungs. There is tight clustering around a ventilation-perfusion ratio of one (A). Shunts are absent (B), as are units with very low (C) or very high (D) ventilation-perfusion ratios.

Figure 1. The multiple inert gas technique shows the relationship between ventilation and blood flow in a lung, represented as a range of ventilation-perfusion ratios. In a normal lung, there is a tight clustering around, A, a ventilation-perfusion ratio of one. Clustering in areas that represent, B, shunts, C, low, and, D, very high ventilation-perfusion ratios are not present.

Range of ventilation-perfusion ratios in asthma

In asthma, ventilation-perfusion ratio relationships fall largely in a bimodal pattern, including areas of low ventilation-perfusion ratios (E) and areas with normal ventilation-perfusion ratios (F). The low ventilation-perfusion ratio areas likely represent alveoli whose airways are occluded with mucus, resulting in reduced ventilation.

Figure 2. The multiple inert gas technique shows the relationship between ventilation and blood flow in a lung, represented as a range of ventilation-perfusion ratios. Patients with asthma have ventilation-perfusion ratios that fall in a bimodal pattern with, E, areas of low ventilation-perfusion ratios, and F, areas with normal ventilation-perfusion ratios.

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Range of ventilation-perfusion ratios in acute respiratory distress syndrome (ARDS)

In patients with acute respiratory distress syndrome (ARDS), complicated changes in ventilation and perfusion produce areas of shunt (G), areas with low ventilation-perfusion ratios (H), areas with normal ventilation-perfusion ratios (I), and other areas with high ventilation-perfusion ratios (J). The low ventilation-perfusion ratio areas may explain why patients with ARDS are difficult to oxygenate in the early phases of their disease.

Figure 3. The multiple inert gas technique shows the relationship between ventilation and blood flow in a lung, represented as a range of ventilation-perfusion ratios. Patients with acute respiratory distress syndrome (ARDS) display areas of, G, shunt, H, areas with low ventilation-perfusion ratios, I, areas with normal ventilation-perfusion ratios and, J, areas with high ventilation-perfusion ratios.

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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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