Proposed mechanism for partial response to oxygen in the hepatopulmonary syndrome

Diffusion-perfusion impairment (also called alveolar-capillary oxygen disequlibrium) occurs in the setting of vasodilation of alveolar capillaries; the partial pressure (or driving pressure) of oxygen in the alveolus is insufficient to achieve equilibration with blood moving near the center of the vessel. When alveolar oxygen is increased, the gradient for diffusion increases and oxygenation improves.