When someone has pulmonary hypertension it means that the blood pressure in the lung arteries is abnormally high. This is venous blood on its way back to the lungs to be re-oxygenated, and the blood pressure in these blood vessels is normally much lower than the blood pressure in the arteries pumping oxygenated blood out of the lungs.
Pulmonary hypertension is caused by constriction of the blood vessels that transport the blood back to the lungs. As it becomes more difficult for the blood to get back to the lungs, the heart has to pump harder to keep the blood moving. Pulmonary hypertension causes stress on the heart, which becomes enlarged. It also causes a build up of fluid in the liver and tissues, which can be seen as a swelling in the legs, for example. Affected patients might also become short of breath and dizzy.
The venous blood vessels can become constricted for many different reasons. Heart and lung diseases such as emphysema or chronic obstructive pulmonary disease can cause the blood vessels to narrow, or they could become blocked by a blood clot from the legs or pelvic veins – known as recurrent pulmonary embolism. The condition can also be brought on by failure of the left heart ventricle, as this is the side of the heart which pumps oxygenated blood back into the body. If this side of the heart is not moving the blood out of the lungs fast enough, it can cause a build up of pressure in the blood vessels waiting to deliver blood into the lungs for oxygenation. There have been some very rare cases of the condition reported in connection with anti-obesity drugs such as Redux and Fen, or Phen.