Pulmonary arterial hypertension (NORD)

Pulmonary arterial hypertension, or PAH, is a rare disorder characterized by high blood pressure in the blood vessels of the lungs, specifically the pulmonary arteries. The pulmonary arteries are blood vessels that carry blood from the right side of the heart through the lungs. So, when pulmonary arterial pressure rises, blood backs up into the right side of the heart, eventually leading to right-sided heart failure. PAH more commonly occurs in middle-aged, biological females.

Individuals with PAH initially experience symptoms like difficulty breathing, fatigue, weakness, chest pain, dizziness, and syncope, or loss of consciousness. As the disease progresses, signs of complications may start appearing, including hemoptysis, or coughing up of blood; and hoarseness due to compression of a nerve in the chest by an enlarged pulmonary artery. Eventually, untreated individuals end up in right heart failure, which causes abnormal fluid collection all over the body, resulting in edema, or swelling of the face and lower limbs; ascites, or fluid collecting in the abdomen, liver enlargement , raised jugular venous pressure, and in the end stages - cyanosis, or abnormal bluish discoloration of the skin due to low blood oxygen levels.

PAH is most often idiopathic, which means that the cause is unknown. Occasionally, PAH can be a heritable disorder due to mutations in genes such as the BMPR2 gene. Without this gene working, there's excessive proliferation, or rapid reproduction of the smooth muscle cells in blood vessels. Another cause of PAH is connective tissue disorders like scleroderma, which damage the endothelial layer of the pulmonary arteries, leading to a release of vasoconstricting substances, causing tightness and narrowing of the blood vessels, such as endothelin 1, thromboxane, and serotonin, as well as smooth muscle hypertrophy, or enlargement. Other causes of PAH include congenital heart disease with left-to-right shunts and portal hypertension, characterized by increased pressure in the portal vein that leads blood from the digestive tract to the liver. The risk of PAH also increases with the usage of some stimulant drugs like cocaine and amphetamines, HIV or human immunodeficiency virus infections, and schistosomiasis, which is caused by parasitic flatworms, called schistosomes, that infect the urinary tract or intestines.

Regardless of the cause, there's vasoconstriction and thickening of pulmonary arterial walls in PAH, resulting in increased resistance to blood flow. This places an added strain on the right heart as it tries pumping blood through a narrower vessel. Over time, overloading of the right ventricle leads to right heart enlargement, which in turn progresses to cor pulmonale, or right-sided heart failure.