Table 1. Classification of pulmonary hypertension based on etiology (9).

Group 1	Idiopathic Heritable Drug induced Associated with conditions like connective tissue disease, HIV, congenital heart disease, schistosomiasis or chronic hemolytic anemia Pulmonary veno occlusive disease (PVOD) and pulmonary capillary hemangiomatosis
Group 2	Left heart diseases Heart failure (systolic or diastolic) Valvular heart disease
Group 3	Underlying lung diseases like chronic obstructive lung disease, interstitial lung disease (ILD) and restrictive lung disease Induced hypoxia due to sleep disorder, alveolar hypoventilation or chronic exposure to high altitude
Group 4	Pulmonary hypertension due to chronic thromboembolic events also known as chronic thromboembolic pulmonary hypertension (CTEPH)