Pulmonary hypertension
Why the low-pressure lung circulation can become a high-pressure one, how constricted, remodelled or lost small arteries raise resistance in five groups of causes, and how the right ventricle first thickens and then fails (cor pulmonale).
By the end, you can
- Describe the normal low-pressure, low-resistance pulmonary circulation and hypoxic pulmonary vasoconstriction.
- Explain how a high left atrial pressure, vasoconstriction, remodelling and loss or blockage of vessels raise pulmonary pressure, and relate them to the five clinical groups.
- Describe medial hypertrophy, intimal fibrosis and plexiform lesions, and why each forms.
- Explain how the right ventricle adapts to a raised afterload and why it can fail (cor pulmonale).
- State the haemodynamic definition (mean pulmonary artery pressure above 20 mm Hg), recognise the main tests and explain how each main treatment acts on the mechanism.
What it is
Pulmonary hypertension is raised pressure in the pulmonary arteries: a mean pulmonary artery pressure above 20 mm Hg at rest, measured at right heart catheterisation. It is a haemodynamic state with many causes, sorted into five clinical groups; in pulmonary arterial hypertension (group 1) the disease starts in the small pulmonary arteries themselves.
3 types to tell apart
- Pre-capillary
- The fault lies in the pulmonary arteries and arterioles (groups 1, 3 and 4, and many in group 5): vascular resistance is raised while the pressure in the left atrium, estimated as the wedge pressure, is normal.
- Post-capillary
- Pressure backs up from a failing left heart or a diseased mitral or aortic valve (group 2): the wedge pressure is raised and, at first, the pulmonary vessels and their resistance are normal.
- Combined pre- and post-capillary
- Long-standing back pressure from the left heart also remodels the pulmonary arteries, so resistance rises too; this carries a worse outlook than back pressure alone.
US spelling: haemodynamic → hemodynamic.
Normal function
A low-pressure circuit that matches blood to air
The pumps the whole cardiac output through the and the and into the lungs, yet it needs little pressure to do so: about 25/10 mm Hg, a mean of about 14 mm Hg, against about 120/80 mm Hg in the aorta. The circuit is short, its arteries are wide, thin-walled and stretchy, and a vast capillary bed lies in parallel, so its resistance is roughly a tenth of the systemic circulation’s.
It also has a large reserve. During exercise, flow can rise several-fold with only a small rise in pressure, because closed capillaries open (recruitment) and open ones widen (distension). The thin-walled right ventricle is built to move volume, not to generate pressure.
Unlike systemic arterioles, which dilate when oxygen is low, small pulmonary arteries constrict when the oxygen in the alveoli they serve falls: hypoxic pulmonary vasoconstriction. Locally it diverts blood from poorly ventilated alveoli to well-ventilated ones, matching perfusion to ventilation. When the whole lung is hypoxic, as at high altitude or in chronic lung disease, the arteries constrict everywhere and pressure rises.
| Feature | Systemic circulation | Pulmonary circulation |
|---|---|---|
| Typical pressure | About 120/80 mm Hg, mean about 90 | About 25/10 mm Hg, mean about 14 |
| Resistance | High, set by muscular arterioles | About a tenth: short, wide, thin-walled vessels |
| Pump | Thick-walled left ventricle | Thin, crescent-shaped right ventricle |
| Arterioles in hypoxia | Dilate, bringing more blood to oxygen-hungry tissue | Constrict, sending blood to better-ventilated alveoli |
| In exercise | Pressure rises | Flow rises several-fold with little rise in pressure (recruitment, distension) |
Typical resting values in a healthy adult; schematic.
Underlying change · Step 1 of 4
Why the pressure rises: back pressure, constriction and lost vessels
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 4
Remodelling of the small pulmonary arteries
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
The right ventricle against a raised afterload
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Breathless and tired: low output and venous congestion
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .