Pulmonary hypertension is largely a misnomer. It is a result of lung blood vessel wall cells increasing in size and number. It is almost like cancer. Top PAH expert explains. What is pulmonary arterial hypertension? Dr. Anton Titov, MD. How to recognize its symptoms? Dr. Anton Titov, MD. What causes pulmonary arterial hypertension? Dr. Anton Titov, MD. Dr. Aaron Waxman, MD. The definition of pulmonary arterial hypertension is misleading. I wish we'd never called it pulmonary artery hypertension. Because all it implies that there is an increase in arterial blood pressure in the pulmonary artery. But increased arterial pressure is a sign of the disease. But it is not main problem in pulmonary arterial hypertension. The pulmonary arterial hypertension is a pathologic process. It results in thickening and stiffening of the blood vessels inside the lung. Those vessels in the lung get stiffer. Then they increase resistance to blood flow. This ultimately drives up pulmonary arterial pressure. Dr. Aaron Waxman, MD. But it is the pathologic change that results in increased stiffness in lung blood vessels. It is increased resistance that imparts the pulmonary arterial hypertension disease state. There is a difficult thing about the pulmonary arterial hypertension. It is also problem with all aspects of pulmonary vascular disease. Dr. Aaron Waxman, MD. The problem is that patients generally present simply with shortness of breath. It is usually shortness of breath that appears with physical exertion. There is no shortness of breath at rest. Shortness of breath is a very common complaint. It is not specific to any disease. People call the disease pulmonary arterial hypertension. It is the name that derives from symptoms and signs of pulmonary arterial hypertension. In reality, the causes of the disease are somewhere else. We don't know what causes Pulmonary arterial hypertension. But there are several associated disease states. Dr. Aaron Waxman, MD. We have learned over the past 15 - 20 years the important discovery about pulmonary arterial hypertension. This is what causes the increased resistance in pulmonary blood vessels. There is abnormal growth, or proliferation of cells. Pulmonary arterial hypertension is almost similar to a neoplastic process. Dr. Anton Titov, MD. You see abnormal growth of smooth muscle cells in certain regions of the pulmonary vascular network. Dr. Anton Titov, MD. You see abnormal growth of endothelial cells and endothelial-like cells in different regions of the lung vascular network. There is also a significant inflammatory component in pulmonary arterial hypertension. Dr. Aaron Waxman, MD. We see increased inflammatory mediator molecules that circulate in blood vessels. There is also almost an invasion of inflammatory cells in pulmonary arterial hypertension. There is also proliferation of connective tissue cells. We also see fibrotic change. Pulmonary arterial hypertension is a very complicated disease. It is much like cancer. Old thinking about pulmonary arterial hypertension focused on a vasoconstrictive process. But is not about constriction of blood vessels in the lungs. Because if it was, it would have been easy to treat patients with pulmonary arterial hypertension many years ago. It is certainly not the first time when the disease gets a name before its nature is understood. Then the name becomes somewhat misleading. Dr. Aaron Waxman, MD. But it is very interesting to know that pulmonary arterial hypertension is a very complicated process. Proliferation of cells lies behind the pulmonary arterial hypertension. Exactly!