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Pulmonary arterial hypertension (PULL-mo-na-ree hi-per-TEN-shun) or PAH is a group of chronic, progressive, and fatal diseases of the small arterial blood vessels of the pulmonary circulation. PAH is a subset of pulmonary hypertension, which encompasses diseases that affect the pulmonary artery tree and are not due to other causes (lung disease or left heart disease).
In pulmonary arterial hypertension, high blood pressure in the pulmonary arteries damages the lungs and heart. If left untreated, PAH quickly becomes life threatening. While no cure yet exists, treatment can slow disease progression.
The pulmonary arteries carry blood from the right side of the heart to the lungs. In the lungs, the blood picks up oxygen to carry to the rest of the body. Just as high blood pressure in the rest of the body damages blood vessels and organs, the high pressure of PAH damages the pulmonary arteries and the tissues of the heart and lungs.
The damage PAH does to these blood vessels and organs starts a vicious cycle. The heart and pulmonary arteries remodel themselves in reaction to the high pressure, which makes them weaker and more prone to problems such as heart failure, clot formation, and bleeding. PAH also causes fluid to build up in the lungs, damaging these tissues and causing the lungs to become less effective at putting oxygen into the blood. These problems all starve the heart of oxygen, causing it to beat more forcefully and making the pressure in the pulmonary arteries even higher.
The processes that actually stimulate the development of PAH are unclear. There are various risk factors (drugs, toxins, associated diseases and conditions) as well as genetic factors that increase the likelihood of developing PAH. There are three biological processes believed to contribute to arterial narrowing.
Vasoconstriction - The muscles within the walls of the arteries tighten up. This makes the inside of the arteries narrower.
Vascular remodeling - The walls of the pulmonary arteries may thicken as the amount of muscle increases in some arteries. Scar tissue may form in the walls of arteries. As the walls thicken and scar, the arteries become increasingly narrow.
In situ thrombosis - Tiny blood clots may form within the smaller arteries, causing blockages.
Types of PAH
Prior to 2003, pulmonary hypertension (PH) was subdivided into two main categories --primary and secondary-- depending on the presence of an identifiable cause. In 2003, the World Health Organization (WHO) introduced a new system for classifying different types of pulmonary hypertension on the basis of similarities in causes and treatments. PH is classified into five groups, with PAH falling into WHO Group I. The following information focuses primarily on PAH or WHO Group I. PAH can be subdivided into three main subgroups.
PAH associated with specific conditions or risk factors
Most cases of PAH fall into this subcategory. These cases may be called "secondary PAH" because they are a secondary effect of the original disease. An important part of treating secondary PAH is to treat the disease that caused it. Diseases and conditions that may cause this type of PAH include:
Autoimmune disease - The occurrence of PAH has been associated with autoimmune disease processes such as rheumatoid arthritis, scleroderma, CREST syndrome, systemic lupus erythematosus, and mixed connective-tissue disease. Frequencies of PAH in these cases range from 6 to 60 percent in scleroderma, 4 to 14 percent in lupus, 21 percent in rheumatoid arthritis, and 15 to 60 percent in connective-tissue diseases.
Sickle-cell disease - Why PAH develops in sickle cell patients is not entirely clear. Proposed causes include a decreased oxygen carrying capacity of the blood cells; the odd sickle cell shape induces the likelihood that the blood cells may stick to the inside walls of the arteries and block blood flow; and extra hemoglobin in the blood leads to a decrease in nitric oxide, which causes the blood vessels to constrict.
Congenital heart disease -- Some types of heart malformation, present at birth, can starve the heart of oxygen and cause it to beat too forcefully.
Liver disease - When liver disease causes high blood pressure in the portal vein, it can also lead to PAH. This syndrome is called portopulmonary hypertension.
HIV disease -- About 0.5 percent of people with AIDS develop PAH, for reasons that are not yet fully understood.
Weight-loss pill use -- Weight-loss drugs such as Fen-Phen, Aminorex, fenfluramine, and phentermin cause PAH in about 7,000 people per year in the United States.
Idiopathic PAH (previously known as primary pulmonary hypertension)
Doctors call PAH idiopathic (id-ee-oh-PATH-ick) when it is not caused by another disease. The word idiopathic means that the cause of a disease is not known. IPAH is rare compared with other types of PAH - about 300 cases per year in the United States. It can affect women or men, but is twice as common in women and affects them earlier in life. IPAH tends to strike women in their 30s and men in their 40s.
Familial PAH
Familial (fah-MILL-ee-al) PAH is an autosomal-dominant disease with genetic linkage to chromosome 2q33. This type of PAH strike members of a particular family at a rate much higher than in the general population. Researchers have come to understand that familial PAH is caused by a genetic mutation that can be inherited. Doctors suspect that similar mutations that either can't be inherited or have not been inherited yet cause isolated cases of PAH.
DNA mistakes in one gene, which produces the protein BMPR2, cause 50 percent of familial PAH and 10 percent of isolated PAH. BMPR2 is a messenger molecule involved in bone formation, but can also affect blood vessels, which is why researchers think it has a role in PAH. Other PAH genes include the one that produces 5-HT(2B), which helps the body use the neurotransmitter serotonin. Serotonin can also affect blood vessels.
Symptoms of PAH
The different types of PAH share identical symptoms. In fact, PAH shares symptoms with so many other types of lung disease that it is difficult to diagnose.
Symptoms of PAH include:
- dyspnea - difficulty breathing
- nonproductive cough
- fatigue, particularly after physical activity
- dizziness and fainting (syncope)
- peripheral edema - swelling of the ankles, feet and legs
- cyanosis - bluish skin and mucous membranes
- angina - chest pain, particularly after activity
- racing pulse
- palpitations - uncomfortable awareness of one's heartbeat
- rarely, hemoptysis - blood in the saliva, coming from the lungs and airway
As the disease develops, particularly if not treated, the weakness increases. In advanced disease, minimal physical activity or even no activity can bring on symptoms.
If you experience any of the above symptoms, see your health care professional immediately for an accurate diagnosis and treatment to relieve your symptoms.
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