What Is Pulmonary Arterial Hypertension?

Pulmonary arterial hypertension (PAH) is a rare type of pulmonary hypertension (PH) that can result from one of several causes, or have no apparent cause. According to the World Health Organization functional classification, it is referred to as group 1 PH.

The disease is characterized by the narrowing of the small blood vessels, called the pulmonary arteries, that transport blood through the lungs. This narrowing restricts blood flow across the lungs, causing high blood pressure, or hypertension, and making the heart work harder to pump blood through the body. A correct diagnosis of PAH is essential to find the best possible treatment for the patient.

Causes of PAH

PAH has many potential causes. These include other diseases as well as treatments that can lead to the narrowing of pulmonary arteries. Examples include:

  • Heart abnormalities, such as congenital heart defects and Eisenmenger syndrome
  • Viral infections, such as HIV
  • Connective tissue disorders, such as scleroderma and lupus
  • Certain medicines, such as methamphetamines
  • Chronic liver disease, or cirrhosis
  • Glycogen storage disease type I, or von Gierke disease, an inherited condition caused by the buildup of a complex sugar called glycogen

Approximately 15 to 20% of PAH patients have familial, or heritable PAH, which is caused by genetic mutations that are passed down to the offspring.

Not all cases of PAH have an identifiable cause, in which case it is referred to as idiopathic PAH. This may be associated with other underlying issues, such as thyroid gland disorders. Notably, one report states that around 25–30% of people diagnosed with idiopathic PAH have a genetic cause for their condition, and thus should be classified instead as heritable PAH.

Symptoms of PAH

As PAH is a progressive disease, the symptoms usually get worse with time unless treated. Complications of PAH are associated with a lack of oxygen in the blood, caused by reduced blood flow through the lungs. Severe shortness of breath is the most frequent initial symptom and can lead to fatigue, weakness, chest pain, dizziness, and fainting. This can make it difficult for patients to undertake even mild exercise, especially at later stages of the disease.

Patients also can experience peripheral edema, or swelling of the ankles, legs, face, and abdomen. PAH also may cause a cough, sometimes with blood.

In its advanced stages, severe PAH can lead to right heart failure, due to the increased workload on the heart, and to patients experiencing cyanosis, a bluish tinge to the skin due to abnormally low levels of oxygen.

Diagnosis of PAH

To reach a diagnosis, clinicians first look at the patient’s symptoms, then run diagnostic tests to exclude other diseases and rule out other causes of PH.

Diagnostic assessments include blood tests, lung function tests, and chest X-rays. Echocardiography, or the use of ultrasounds to check the size and condition of the heart, and electrocardiography, which measures electrical activity, also may be used to get a diagnosis. The patient’s ability to exercise may be tested using the six-minute walk test, which measures how far the patient can walk in six minutes.

If PAH is suspected, an invasive test called right heart catheterization will most likely be conducted. In this test, which measures blood pressure in the pulmonary arteries and cardiac function, a doctor guides a small, hollow tube called a catheter into the pulmonary artery.

A diagnosis of familial PAH may be given based on family history and genetic testing, which is used to check whether a person has a particular disease-causing mutation.


Last updated: June 22, 2021


Pulmonary Hypertension News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.