Pulmonary hypertension (PH) is defined as a mean pulmonary artery pressure which is greater than 25 mmHg when at rest or 30 mmHg with exercise, as measured by right heart catheterization. Previously, PH was defined as a systolic pulmonary artery pressure greater than 40 mmHg, which also corresponds to a tricuspid regurgitant velocity on Doppler echocardiography of 3.0 to 3.5 m/sec.
The term - pulmonary hypertension - is composed of the word "pulmonary" that pertains to the lung, "hyper" pertaining to high, and "tension" which pertains to blood pressure. Pulmonary hypertension then is also pulmonary high blood pressure.
Pulmonary hypertension (PH) is a state wherein the blood vessels inside the lungs have too-high pressure which is caused by many things. PH is hard to diagnose because its symptoms are very vague until it gets worse.
Here's what happens in a pulmonary hypertension, inside the lungs are tiny blood vessels called capillaries. Inside, each capillary is lined with a special kind of cell called endothelial cells, while the outside is covered with smooth muscle cells. The endothelial cells normally keep blood from leaking out of the blood vessel while the smooth muscle cells normally allow the vessel to expand or shrink, depending on how much blood is inside the capillary.
In PH, some of the endothelial cells lining the capillaries are weakened, and may even be enlarge. As these cells line the inside of the capillaries, if they get bigger they make the inside of the blood vessel smaller which then give less room for blood to pass through and blood may then leak out as well.
At the same time, the outer smooth muscle cells shrink. This muscle shrinkage tightens the blood vessels (this is like holding a sponge in the hand and squeezing it), the muscle cells on the outside of the blood vessel squeeze, making the capillary smaller and this increases the pressure inside them.
The high pressure in the capillaries then result to a resistance to the heart's efforts to pump blood through them. When this happens for most capillaries, the flow of blood between the heart and lungs is seriously reduced.
The heart's right ventricle though, which pushes blood through the lungs, tries to overcome this extra resistance by working harder. However, it can't keep this up forever and eventually, the extra work the heart's right ventricle has to do permanently damage it which then results to heart failure.
