What 'high pressure' means here
The lung circulation is normally a low-pressure system — far gentler than the high-pressure circuit feeding the body. Pulmonary hypertension (PH) means the mean pulmonary artery pressure is abnormally high. This is a different number from the blood pressure measured on your arm, which reflects the body's circulation, not the lung's.
Pressure in the lung circuit — a sense of scale Systemic arteries (the arm cuff): ~120 / 80 mmHg Normal pulmonary artery (mean): < 20 mmHg Pulmonary hypertension (mean): >= 20 mmHg (at rest) Why the lung runs low: - thin-walled vessels, easy to over-stretch - the whole output of the heart passes through every minute - a large reserve of vessels can open up during exercise Key idea: even 'mild' PH burdens a right ventricle that was never built for high pressure.
Symptoms are quiet at first and easy to miss: gradually worsening breathlessness on exertion, tiredness, and later fainting or swollen ankles. Because the early picture is so non-specific, PH is often diagnosed late — one reason it pays to know the concept exists.
Many roads to the same pressure
Pulmonary hypertension is not one disease but a final common state with several distinct causes — and the treatment depends entirely on which road led there.
- Disease of the lung's own small arteries — these vessels narrow and stiffen; this is the rare, severe form treated with specialized vessel-relaxing drugs.
- Left-heart disease — a weak or stiff left heart backs pressure up into the lungs; this is the most common cause and overlaps with cardiogenic pulmonary edema.
- Chronic lung disease and low oxygen — conditions like COPD and pulmonary fibrosis cause vessels to tighten; raising oxygen helps.
- Old, unresolved clots — repeated pulmonary emboli that never fully cleared can scar the vessels into a chronic, potentially operable form of PH.
Measuring it, and what it does to the heart
An ultrasound of the heart (echocardiogram) can estimate lung pressure and is the usual first step. But the certain answer comes from right heart catheterization — a thin tube threaded through a vein into the pulmonary artery to measure the pressure directly. It is the gold standard, and it also reveals whether the cause sits before or beyond the lung's vessels.
Whatever the cause, sustained high pressure means the right ventricle must work harder every single beat. At first it thickens to cope, but a heart built for low pressure eventually tires. Chronic right ventricular strain driven by lung disease has its own name: cor pulmonale — literally 'lung heart'. As the right heart fails, fluid backs up into the body, producing the swollen legs and congested liver that often bring patients in.