Pulmonary Hypertension: Overview

Reviewed by Marjorie Patricia George, MD

Pulmonary hypertension refers to a condition in which high blood pressure exists within the vessels of the lungs. Normally, venous (low oxygen) blood returns from the body to the right side of the heart. The blood is pumped to lungs via the pulmonary arteries. Breathing brings oxygen to venous blood in the lungs, turning it into arterial (high oxygen-containing) blood. Arterial blood returns through the pulmonary veins to the left side of the heart, where it is pumped to the rest of the body to deliver oxygen to organs and tissues.



Pulmonary hypertension has been classified as primary (without obvious cause, or idiopathic) or secondary (occurring as a result of another disease). Although this is still referenced in medical texts, the revised World Health Organization (WHO) classification system does away with these definitions. The WHO divides pulmonary hypertension into five categories. These categories include:

  • WHO Group I: Pulmonary hypertension due to a disease of the arteries themselves, such as idiopathic, or hereditary, or related to autoimmune disease.

  • WHO II: Pulmonary hypertension due to increased pressure on the left side of the heart.

  • WHO III: Pulmonary hypertension due to chronic lung disease, low oxygen levels or sleep disorder.

  • WHO IV: Pulmonary hypertension due to blood clots in the lung.

  • WHO V: Pulmonary hypertension associated with diseases that don’t fall into the other four categories, such as sickle cell disease.

See how your heart can affect your breathing in our infographic explaining the heart/lung connection.

Learn about the Pulmonary Hypertension Center at National Jewish Health.


Associated Conditions

Pulmonary hypertension can occur in isolation or, more commonly, with diseases of the lungs and heart. Pulmonary hypertension in the absence of other diseases is very rare and generally idiopathic or familial in nature. This kind of pulmonary hypertension is referred as pulmonary arterial hypertension (PAH). Pulmonary arterial hypertension can also be associated with autoimmune diseases; drug use such as methamphetamines or diet drugs; human immunodeficiency virus (HIV); liver disease and congenital heart disease.

Pulmonary hypertension is commonly associated with a variety of lung conditions with low oxygen levels. These include COPD, emphysema, interstitial lung disease, chronic pulmonary blood clots or sleep apnea. When pulmonary hypertension arises from cardiac conditions such as heart failure or heart valve disease, it is referred to as a pulmonary venous hypertension. However, it is important to remember that pulmonary hypertension can be associated with multiple causes.


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