Pulmonary arterial hypertension (PAH) is a rare type of pulmonary hypertension that can be the result of one of several causes, or by no apparent cause. It is sometimes referred to by the World Health Organization (WHO) functional classification as group 1 pulmonary hypertension.

The disease is characterized by the narrowing of the smaller blood vessels that transport blood through the lungs, called the pulmonary arteries. This restricts blood flow through the lungs, causing high blood pressure, or hypertension, and making the heart work harder to pump blood through the body. Diagnosing the correct type of pulmonary hypertension is essential, as it can change what type of treatment is required.

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:

Approximately 15-20 percent of PAH patients have familial, or heritable PAH, which is caused by genetic mutations that are passed down through the family.

Not all cases of PAH have an easily identifiable cause, in which case it may be referred to as idiopathic PAH. This may be associated with other underlying issues such as thyroid gland disorders.

Symptoms of PAH

As PAH is a progressive disease, the symptoms usually get worse with time unless treated. The most common early symptoms 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 pains, dizziness, and fainting. This can make it difficult for patients to undertake even mild exercise, especially at later stages of the disease.

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

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

Diagnosis of PAH

PAH is initially diagnosed in the same way as pulmonary hypertension. 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 pulmonary hypertension.

There are many diagnostic assessmentsincluding blood tests, lung function tests, chest X-rays, echocardiography, and electrocardiography that can be used to diagnose PAH. 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, a test called right heart catherization will most likely be conducted. This test measures the blood pressure in the pulmonary arteries and the right side of the heart, and can also be used to estimate the severity of the disease. 

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

Treatment of PAH

Although there is currently no cure for PAH, there are several therapies that can help manage its symptoms and slow the progression of the disease.

General therapies are used to treat all types of pulmonary hypertension. These include blood-thinners, oxygen therapy, digoxin, and diuretics. In some severe cases, clinicians may recommend patients undergo surgery, such as a lung transplant.

Several medications have been developed to specifically treat PAH, and many are not approved to treat other types of pulmonary hypertension. These are briefly described below.

Prostacyclin-based therapies

There are several therapies that act to mimic prostacyclin, a substance naturally produced by the body. Prostacyclin can widen, or dilate, blood vessels, which improves blood flow and increases oxygen supply around the body. Some examples include Flolan/Veletri (epoprostenol); Orenitram (treprostnil taken orally); Remodulin (injected treprostinil); Tyvaso (inhaled treprostinil), and Ventavis (iloprost).

Endothelin receptor antagonists

Endothelin receptor antagonists act to block the action of endothelin, a substance produced by the body that can cause the blood vessels of the lungs to narrow. Examples include Tracleer (bosentan); Opsumit (macitentan); and Letairis (ambrisentan).

Phosphodiesterase-5 inhibitors

Phosphodiesterase-5 inhibitors act to widen the blood vessels by blocking the enzyme phosphodiesterase-5 (PDE-5), which normally breaks down cGMP. Higher levels of cGMP increases signaling to relax and widen the blood vessels of the lungs. Examples include Revatio (sildenafil) and Adcirca (tadalafil).

Other information

Two additional medications, Uptravi (selexipag) and Adempas (riociguat), act through different mechanisms to widen the blood vessels of the lungs.


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