Hypoxaemia and liver cirrhosis: a new argument in favour of a "diffusion-perfusion defect".

Liver cirrhosis is sometimes associated with very severe hypoxaemia, which is thought to be the result of intrapulmonary vascular dilatations (IPVDs). These vascular abnormalities, although close to the gas exchange units, are so dilated that diffusion of oxygen molecules to their centre is impaired, causing an increase in alveolar-arterial oxygen tension difference (P(A-a)O2). On the other hand, administration of 100% oxygen provides enough driving pressure to overcome this relative diffusion defect and rules out a true intrapulmonary shunt. We report a case in which, in spite of a normal increase in arterial oxygen tension (PaO2) under 100% oxygen, exercising results in a marked impairment of oxygen exchange and a large intrapulmonary shunt. This is probably due to the increased cardiac output and preferential blood flow through these low resistance IPVDs.