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.
Over time, the right heart is enlarged. This explains why the impact of PAH is not limited to the arteries in the lungs but has a direct impact on the heart. In some cases, over a period of time, the right heart will start to enlarge and decompensate. As a result, less blood will circulate through the lungs, picking up less oxygen overall. This may make people with PAH feel tired and breathless. If PAH is not treated, the right heart will start to fail.
Connective Tissue Disease-Associated Pulmonary Arterial Hypertension (CTD-PAH)
Connective tissue disease-associated pulmonary arterial hypertension (CTD-PAH) describes a group of autoimmune diseases that can cause PAH.
Examples include systemic sclerosis (scleroderma) and systemic lupus erythematosus (SLE) or mixed connective tissue disease.
By far, systemic sclerosis is the main cause of CTD-associated PAH. It is important to screen for CTD-PAH because there may be no symptoms or very mild symptoms at the early stage.
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