Pulmonary arterial hypertension (PAH) is a rare lung disease, where it becomes extremely difficult for the heart to pump blood. This leads to a strain on the heart and it becomes larger and weaker. This article examines the causes of this disease. It discusses the classification of the disease based on the cause.

When we look at the symptoms and causes of pulmonary arterial hypertension, we need to understand the causes of this disease. There are many reasons why a person can develop PAH. It is believed that in nearly 15 to 20% of cases, it is inherited from parents.

There are many other reasons why one can develop PAH. This is related to heart diseases, defects in the heart, lung diseases, and other conditions. In some patients, there is no apparent cause, in which case, it is termed as idiopathic pulmonary arterial hypertension.

PAH has been classified into five groups based on the cause of the disease, namely Group I, II, III, IV, and V.

Group I
This group includes idiopathic PAH, where the cause is not known. It also includes PAH that is inherited. This happens because of the mutation of a gene. This is referred to as heritable PAH.

Some drugs like methamphetamines can lead to PAH. Congenital heart disease, which occurs because of abnormalities at birth, can cause PAH.

There are other conditions that can lead to PAH. This includes liver disease, HIV infection, schistosomiasis (a parasitic infection), and connective tissue disorders like scleroderma.

Group II
Under Group II, PAH is caused by heart disease in the left side of the heart. Valvular heart disease in the left side, like aortic valve disease, can lead to artery problems causing PAH.

The left ventricle, which is the lower left chamber in the heart may fail, leading to PAH.

Group III
Group III classification is done based on lung disease. Emphysema is a disease related to COPD (Chronic Obstructive Pulmonary Disease). COPD can cause PAH. Pulmonary fibrosis is a lung disease, which leads to scarring in lung tissue, leading to PAH.

Sleep apnea is a sleep disorder where a person suddenly wakes up from sleep gasping for breath. This can lead to the development of PAH. Those who live in very high altitudes face a higher risk of developing PAH.

Group IV
Under Group IV classification, PAH caused by blood clots is included. This is referred to as chronic thromboembolic pulmonary hypertension. This happens because of blood clots developing in the pulmonary emboli in the lungs.

Group V
In the last group, classification is done based on conditions with unclear reasons for developing PAH. This includes the following:

• Blood disorders
• Sarcoidosis and other disorders in the body
• Glycogen storage disease and other such metabolic disorders
• Tumors that may be pressing on the lungs causing artery constriction and PAH.