[Definition, concept and pathophysiology of pulmonary hypertension].

Intravenous prostacyclin infusion has been introduced as breakthrough to the treatment of primary pulmonary hypertension(PPH) followed thus far inevitably by calamitous outcome and has recently promised a favorable outlook. Pulmonary hypertension (PH) is defined as pulmonary artery mean pressure exceeds 25 mmHg at rest in a lying position. The concept of PH was discussed historically down to date and has been usually used for the patient with sustained PH in vascular origin including PPH. Pathophysiology relating to the cause of PH has been focused on unexplained PH which is PH due to collagen, hepatoportal, congenital cardiac diseases, HIV infection and anorexigenics. Various intrinsic chemical mediators such as TXA2, ET-1, serotonin, eNOS, K channel and their antagonists give rise to PH. Genetics of PH was discussed around Gene PPH-1 disclosed by Genome Project. However, further attention should be paid for enormous pulmonary vascular reserve in normals, because PH occurs only when this reserve must be reduced to a critical level before medial muscular hypertrophy develops.