Pulmonary Hypertension
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Direct answer
Pulmonary hypertension is persistently raised pressure in the pulmonary circulation — mean pulmonary artery pressure above 20 mm Hg at rest by current haemodynamic definition, with older textbooks quoting 25 mm Hg. It is classified into five WHO groups: pulmonary arterial hypertension (including idiopathic disease linked to BMPR2 mutations), disease from left heart failure, from chronic lung disease and hypoxia, from chronic thromboembolism, and miscellaneous causes. Vascular pathology progresses from medial hypertrophy through intimal fibrosis to complex plexiform lesions, and the end result is right ventricular hypertrophy and failure — cor pulmonale.
What you must remember
- Definition: mean pulmonary artery pressure above 20 mm Hg at rest (older texts: above 25 mm Hg); pulmonary vascular resistance is central to the modern definition.
- WHO group 1 (pulmonary arterial hypertension): idiopathic and heritable forms (BMPR2 mutation, young women), connective-tissue disease (systemic sclerosis), congenital left-to-right shunts, portal hypertension, drugs such as anorexigens, and schistosomiasis in endemic regions.
- Groups 2-5: left heart disease (the commonest overall cause), chronic hypoxic lung disease, chronic thromboembolic obstruction, and miscellaneous conditions such as haematological and glycogen storage disorders.
- Heath-Edwards grading: grade I medial hypertrophy of small pulmonary arteries; II intimal proliferation; III concentric laminar intimal fibrosis; IV plexiform lesions; V angiomatoid lesions and dilatation lesions; VI necrotising arteritis — grades IV-VI indicate severe, advanced disease.
- Plexiform lesion: a tuft of capillary-like channels within a dilated pulmonary artery, the histological hallmark of severe pulmonary hypertension, typical of group 1 disease.
- Mechanisms in hypoxic disease: hypoxic pulmonary vasoconstriction, vascular remodelling and loss of capillary bed in COPD and interstitial fibrosis — the commonest route to cor pulmonale in India.
- Eisenmenger complex: large left-to-right shunts remodel the pulmonary vasculature until flow reverses, with cyanosis, haemoptysis and paradoxical emboli; targeted pulmonary vasodilator therapy and transplantation are options per current guidance.
Common confusion
Primary (idiopathic) pulmonary arterial hypertension is a plexiform-lesion disease of young women with a BMPR2 link, whereas secondary pulmonary hypertension — by far the commoner — follows left heart failure, mitral stenosis, COPD or recurrent emboli and needs no such genetics. Do not confuse cor pulmonale (right heart disease from pulmonary causes) with the right ventricular failure of left heart disease. Plexiform lesions indicate severe group 1 disease; thromboembolic pulmonary hypertension instead shows organised, recanalised thrombus webs.
Exam-focused takeaway
Stems describe a young woman with exertional syncope and a loud pulmonary component of the second sound (idiopathic pulmonary arterial hypertension), a COPD patient developing oedema (cor pulmonale), or a photomicrograph of a plexiform lesion. Questions test the WHO group of a given cause, the order of Heath-Edwards grades, and the shunt reversal of Eisenmenger syndrome. Answer from cause to vessel lesion to cardiac consequence.
Frequently asked questions
What is the current haemodynamic definition of pulmonary hypertension?
Mean pulmonary artery pressure above 20 mm Hg at rest; older textbooks and exams may still quote 25 mm Hg.
What is a plexiform lesion?
A tuft of thin-walled capillary channels arising within a dilated small pulmonary artery — the hallmark histology of severe pulmonary arterial hypertension.
Which group of pulmonary hypertension is commonest?
Group 2, from left heart disease such as left ventricular failure and mitral valve disease.
What causes idiopathic pulmonary arterial hypertension?
Largely unknown; heritable cases involve BMPR2 mutation disrupting vascular growth signalling, mostly in young women.
What is cor pulmonale?
Right ventricular hypertrophy, dilatation or failure caused by pulmonary hypertension secondary to lung or pulmonary vascular disease.