Pulmonary Arterial Hypertension (PAH) is characterised by a vasculopathy which primarily affects the distal pulmonary arteries. A combination of vasoconstriction, cellular proliferation in all layers of the vessel wall and perivascular adventitial thickening due to inflammatory infiltrates and increased extracellular matrix deposition all contribute to raised pulmonary vascular resistance.
In addition, obstructive remodelling of the vessel due to microthrombosis-in-situ and plexiform lesion formation further elevates the pulmonary vascular resistance.
Although the exact processes behind the initiation of PAH are, as yet, unknown, the aetiology is multifactorial and a multi-hit hypothesis in the formation of the disease exists. These potential hits include genetic predisposition, co-existing disease and environmental exposure, such as appetite suppressants and amphetamines.