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WHO Group 1: Pulmonary Arterial Hypertension (PAH)

Pulmonary arterial hypertension is a disease in which blood is not able to circulate normally through the lungs due to narrowing of the pulmonary arteries. Over time, blood cells stiffen and thicken, leading to increases in pressures and swelling of the heart.

The average (mean) pressure within the pulmonary arteries (also known as mPAP) is normally at 15-25 mmHg. For someone living with PAH, mPAP is equal to or higher than 25 mmHg.

What causes PAH?

The exact cause of PAH is not well understood, although new progress in research is always happening. The condition can be:

WHO Group 2: PH Associated with Left-Sided Heart Disease

Left-sided heart disease can lead to the failure to properly pump blood around the circulatory system. This causes a build-up of pressure, which leads to the development of pulmonary hypertension.

What causes PH Due to Left-Sided Heart Disease?

  • Left-sided congestive heart failure
  • Mitral valve disease
  • Other heart diseases

WHO Group 3: PH Associated with Lung Disease

Lung diseases can lead to hypoxia (lack of oxygen) and other problems in the blood. This can lead to an increase in blood pressure and cause the development of PH.
What causes PH Due to Lung Disease?

  • COPD
  • Pulmonary fibrosis
  • Sleep apnea
  • Other lung diseases

WHO Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH)

Chronic thromboembolic pulmonary hypertension (CTEPH) is caused by blood clots in the pulmonary arteries that don’t clear up, causing scarring in the pulmonary arteries. Scarring and blockage causes a build-up of pressure in the circulatory system, which leads to the development of CTEPH.

Click here to find out more about CTEPH and how it's treated.

WHO Group 5: PH Caused by Various Other Diseases

Pulmonary hypertension can be caused by various other diseases. The mechanisms of a lot of these relationships are unclear.
What are some known causes?