Quantification of oxygen exchange inefficiency in interstitial lung disease

Hypoxemia (low PaO₂) is a hallmark of moderate to-severe interstitial lung disease (ILD). Ventilation/ perfusion (V/Q̇) mismatch is a dominant mechanism, ̇ with a secondary role for diffusion limitation (at least at rest). In some patients, intrapulmonary shunting and impaired alveolar exchange of oxygen (O₂) can occur ('physiological' shunt [Shunt_PHYS)]), leading to severe, irreversible or nearly irreversible hypoxemia. Because of the effect of gravity on pulmonary blood flow, any shunted fraction can increase in the upright position when extensive alveolar filling is present in dependent areas of the lung in the setting of relatively preserved capillary perfusion. (author)