Pulmonary hypertension (PH) 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 where it is pumped to lungs via the pulmonary arteries. Breathing brings oxygen to venous blood in the lungs, turning it into arterial (high oxygen) blood. Arterial blood returns to the left side of the heart through the pulmonary veins where it is subsequently pumped to the rest of the body.
Healthy pulmonary arteries of the lungs are elastic, expanding and contracting with each beat of the heart. In PH, arteries stiffen and thicken, leading to increased resistance to blood passing through the vessel thereby increasing pressure. Higher pulmonary pressure can lead to shortness of breath, low oxygen levels, chest pain, near-fainting/fainting, heart rhythm problems, and in its more advanced form, heart failure.
Pulmonary hypertension was previously classified as primary (without obvious cause, or idiopathic) or secondary (occurring as a result of another disease). Although this terminology is still referenced in medical text, the revised World Health Organization classification system does away with these definitions and instead divides PH into 5 different categories based upon mechanism of disease.
PH can occur in isolation or, more commonly, with diseases of the lungs and heart. PH in the absence of other diseases is very rare and generally idiopathic or familial in nature. This kind of PH is referred as pulmonary arterial hypertension (PAH).
PH is commonly associated with a variety of lung conditions characterized by low oxygen levels. These include emphysema, asthma, interstitial lung disease, chronic pulmonary blood clots or sleep apnea. When pulmonary hypertension arises from cardiac conditions such as heart failure, heart valve disease, or congenital heart disease, it is referred to a pulmonary venous hypertension.
Other important disease states associated with PH include connective tissue diseases (scleroderma, lupus, rheumatoid arthritis), sarcoidosis, hyperthyroidism, liver disease, sickle cell disease and bone marrow disorders. Amphetamine use such as meth or the diet drug Fen-Phen has been linked to the development of PH. Oftentimes multiple causes of PH are present.