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Pulmonary Hypertension: Overview

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This information was reviewed and approved by Marjorie Patricia George, MD (1/31/2020).

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 the lungs via the pulmonary arteries. Oxygen is transferred into the blood at the alveolus-capillary interface, and then 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.

Classifications of Pulmonary Hypertension

There are five different types of pulmonary hypertension (PH). These types are categorized into groupings based on the causes and treatments of the disease. The groups are known as the World Health Organization (WHO) classification system.

WHO Groups of Pulmonary Hypertension

GroupNameCaused byRisk Factors
1Pulmonary Arterial Hypertension (PAH) —due to a disease of the arteries themselves
Increased stiffness, narrowing or scarring of the pulmonary arteries stresses the heart, losing its ability to pump enough blood through the lungs.
  • Family history
  • Connective Tissue Diseases (scleroderma, lupus)
  • HIV
  • Liver Disease
  • Cocaine & Meth Use
  • Unknown Cause (idiopathic) 
2PH Due to Left Heart Disease — heart failure or heart valve problems
The left side of the heart does not pump correctly, creating a back pressure into the lungs.
  • Atrial Fibrillation
  • Coronary Artery Disease (CAD)
  • Heart Valve Disorders
  • HFpEF (diastolic heart failure)
3PH Due to Chronic Lung Disease and Hypoxia (low oxygen levels) including Sleep Disorders
Shortage of oxygen causes the arteries in the lungs to tighten.   
  • COPD
  • ILD/Pulmonary Fibrosis
  • Sleep Disordered Breathing
  • Chronic High Elevation Exposure
  • Lung Developmental Defects
  • Alveolar Hypoventilation Disorders
4PH Due to Chronic Arterial Obstructions  —   blockages in the pulmonary arteries
Blood clots that the body can’t dissolve or other obstructions block pulmonary arteries.
  • Recurring Blood Clots
  • Blood Clotting Disorders
  • Chronic Thromboembolic Pulmonary Hypertension
5PH from Unknown CausesNot well understood.
  • Blood Disorders (Sickle Cell Disease)
  • Systemic Disorders (sarcoidosis & histiocytosis) 
  • Metabolic Disorders
  • Chronic Kidney Failure
  • Splenectomy  


As the chart below shows, most patients are diagnosed with PH due to left heart disease (Group 2) and/or PH due chronic lung disease with low oxygen levels, Group 3.  


Chart source: Wijeratne, D. T., et al. (2018). Increasing Incidence and Prevalence of World Health Organization Groups 1 to 4 Pulmonary Hypertension: A Population-Based Cohort Study in Ontario, Canada. Circulation. Cardiovascular Quality and Outcomes, 11(2), e003973.


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 is often idiopathic, associated with autoimmune disease or familial in nature. This kind of pulmonary hypertension is referred as pulmonary arterial hypertension (PAH). Pulmonary arterial hypertension can also be associated with 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 sometimes referred to as pulmonary venous hypertension. And while there are specific types of pulmonary hypertension, it is important to note that pulmonary hypertension can be associated with multiple causes.

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

Learn about the Pulmonary Hypertension Program at National Jewish Health.