Table 2.

Clinical classification of pulmonary hypertension

Type of pulmonary hypertension	Causes
Grade 1
Pulmonary arterial hypertension	Idiopathic
	Heritable: (eg BMPR, ALK1, mutations)
	Drugs and toxins
	Connective tissue diseases
	HIV infection
	Portal hypertension
	Congenital heart disease
	Schistosomiasis
	Persistent pulmonary hypertension of the newborn
Pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis
Grade 2
Pulmonary hypertension resulting from left heart disease	LV systolic dysfunction
	LV diastolic dysfunction
	Valvular heart disease
Grade 3
Pulmonary hypertension resulting from lung diseases and/or hypoxia	Chronic obstructive pulmonary disease
	Interstitial lung disease
	Other pulmonary diseases with mixed restrictive and obstructive patterns
	Sleep-disordered breathing
	Alveolar hypoventilation disorders
	Chronic exposure to high altitude
	Developmental abnormalities
Grade 4
Chronic thromboembolic pulmonary hypertension
Grade 5
Pulmonary hypertension with unclear and/or multifactorial mechanisms	Haematological disorders (eg myeloproliferative disorders, splenectomy)
	Systemic disorders (eg sarcoidosis, pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis, neurofibromatosis, vasculitis)
	Metabolic disorders (eg glycogen storage disease, Gaucher's disease, thyroid disorders)
	Others: tumoural obstruction, fibrosing mediastinitis, chronic renal failure

ALK = anaplastic lymphoma kinase; BMPR = bone morphogenetic protein receptor; LV = left ventricular