Worsening Hypoxia Post Lung Transplant: What has Changed?

Platypnoea-orthodeoxia is a rare, but under-diagnosed clinical entity, characterised by postural hypoxia and breathlessness. Underlying pathology is inter-atrial shunt or pulmonary vascular malformation, but what anatomical distortion / physiological alterations initiates right to left shunt, usually against the pressure gradient remains unknown.