Perspective for Part I

The lungs are the primary organs of the respiratory system in vertebrates, other than fish, that function as an efficient gas exchanger. This respiratory system is physically and physiologically connected to the cardiovascular system to extract oxygen from the atmosphere and transfer it into the bloodstream and to release carbon dioxide from the bloodstream into the atmosphere. The normal pulmonary circulation, in contrast to the systemic circulation, has low pressure because of a low-resistant vascular bed that enables highly efficient gas exchange between the millions of alveoli and capillaries. Pulmonary hypertension (PH) is a rare pulmonary arterial disease with a high mortality and morbidity although treatment options have improved in the last decades. PH is defined by a mean pulmonary artery pressure (mPAP) greater than or equal to 20 mmHg at rest and is classified into five main subgroups based on the etiology and hemodynamic criteria. Because PH is heterogeneous at the genetic and molecular levels, a deeper understanding is required for the development of more effective therapies.