Asthma and ARDS as examples of altered ventilation-perfusion ratios

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.

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.

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.

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