What is pulmonary hypertension?
Pulmonary hypertension (PH) is a rare lung disorder in which the blood pressure in the pulmonary artery (the artery leaving the right side of the heart and going to the lungs) rises far above normal levels. The raised pressure increases the resistance to blood flowing through the vessels. This increased resistance puts a strain on the heart's right ventricle, which has to work harder than usual to move enough blood through the lungs. At the same time as the pressure rises, the walls
of the network of blood vessels supplying the lungs become thicker.
The pulmonary artery is the blood vessel carrying oxygen-poor blood from the heart to the lungs. Pulmonary hypertension is present when the mean pulmonary artery pressure is greater than 25mmHg at rest or 30mmHg with exercise. This abnormally high pressure (pulmonary hypertension) is associated with changes in the small blood vessels in the lungs, resulting in an increased resistance to blood flowing through the vessels. This increased resistance, in turn, places a strain on the heart as it has to work against a higher resistance to pump blood to the lungs.
Pulmonary hypertension begins when tiny arteries in your lungs become narrow or blocked. This causes increased resistance to blood flow in your lungs, which in turn raises pressure within the pulmonary arteries. As the pressure builds, your heart's right ventricle must work harder to pump blood through your lungs, eventually causing the heart muscle to weaken and sometimes to fail completely. Blood travels from the right side of the heart through the pulmonary arteries into the lungs. There, carbon dioxide is removed from the blood and oxygen is added to it. Normally, the right side of the heart is weaker than the left side, because relatively little muscle and effort are needed to push the blood through the pulmonary arteries. In contrast, the left side of the heart is stronger and more muscular because it has to push blood through the entire body. Likewise, blood pressure through the pulmonary arteries is lower than that of the general circulation. While the pressure in the general circulation is normally about 120/80 mm Hg, in the pulmonary arteries it is only 25/15 mm Hg.
Pulmonary hypertension is a lung disorder in which blood pressure in the pulmonary artery rises above normal levels. If the pressure of the blood in the pulmonary arteries is abnormally high, the condition is called pulmonary hypertension. Over time, the increased pressure damages both the large and small pulmonary arteries. The walls of the smallest blood vessels thicken and are no longer able to transfer oxygen and carbon dioxide normally between the blood and the lungs. Thus, the levels of oxygen in the blood may fall. The low oxygen level can cause narrowing (constriction) of the pulmonary arteries. These changes contribute further to the increased pressure in the pulmonary circulation.
Pulmonary hypertension is conventionally divided into primary and secondary types. Primary pulmonary hypertension is considered idiopathic (of unknown origin). It occurs sporadically with no family history of the disorder and in a familial form. Secondary pulmonary hypertension may be due to congenital heart disease, pulmonary embolism, portal hypertension, collagen vascular disorders (such as lupus), sarcoidosis, and HIV infection. Regardless of whether pulmonary hypertension is primary or secondary, the disorder results in thickening of the pulmonary arteries and narrowing of these blood vessels. In response, the right side of the heart works harder to move the blood through these arteries and it becomes enlarged. Eventually overworking the right side of the heart may lead to right-sided heart failure, resulting in death.