Pulmonary arterial hypertension (PAH) is a condition of high lung pressure in the blood vessels leading from the heart to the lung.
Pulmonary arterial hypertension belongs to Pulmonary Hypertension Group 1 based on the classification schema published in the 2013 5th World Symposium in Pulmonary Hypertension held in NICE. It has several subgroups (see Table 1) such as idiopathic, heritable or familial, related to drugs and toxins or associated with certain conditions such as connective tissue disease, HIV infection, portal hypertension, congenital heart disease or schistosomiasis.
1. Pulmonary arterial hypertension
1.1 Idiopathic PAH
1.2 Heritable PAH
1.2.2 ALK-1, ENG, SMAD9, CAV1, KCNK3
1.3 Drug and toxin induced
1.4 Associated with:
1.4.1 Connective tissue disease
1.4.2 HIV infection
1.4.3 Portal hypertension
1.4.4 Congenital heart diseases
1′ Pulmonary veno-occlusive disease and/or pulmonary capillary hemangiomatosis
1′′. Persistent pulmonary hypertension of the newborn (PPHN)
Source: Abridged version from Simonneau et al. Classification of Pulmonary Hypertension
In PAH, the pulmonary arteries constrict and become increasingly narrow. Progression of the disease is characterised by inflammation and remodeling of the blood vessels. The endothelial cells multiply, the smooth muscle cells increase in size and number and the fibroblasts cells multiply. Consequently, the walls of these vessels become thicker and less flexible. This narrowing of the pulmonary arteries restricts blood flow to the lungs and causes an increase in resistance, which causes the blood pressure in the arteries to rise (Figure 1).