The term PH is used if the average pressure in the pulmonary arterial system is ≥ 25 mmHg. Values below 20 mmHg are regarded as normal, values of between 21 and 24 mmHg are described as borderline (“borderline PH”). The supplementary definition of PH used to date – an increase in mPAP to values > 30 mmHg on exertion – has been dropped. Older people, in particular, reach high levels such as this relatively often on exertion, without suffering from pulmonary hypertension . The criterion of increased pulmonary vascular resistance of 2-3 Wood units is no longer part of the current definition either. Precapillary, pulmonary arterial hypertension is characterised by a pulmonary capillary wedge pressure of <15 mmHg.
Pulmonary arterial hypertension (PAH) covers a group of diseases characterised by the proliferation and remodelling of the distal pulmonary arteries. Loss of the pulmonary vasculature leads to an increase in right ventricular afterload and right heart insufficiency .
The prototype PH, idiopathic pulmonary arterial hypertension (iPAH), is an extremely rare disease with an incidence of 1 – 2 per million . The prevalence of PAH is about 15 per million . Idiopathic PAH affects women more often than men. The heritable forms of PAH (hPAH) are statistically linked to mutations in the “bone morphogenetic protein receptor II” (BMPR II) gene. Secondary forms of PAH (aPAH) are far more common; they include PAH secondary to connective tissue diseases, HIV infection, portal hypertension, congenital heart diseases, schistosomiasis and chronic haemolytic anaemia. All forms are diagnosed at a late stage because of their gradual onset and nonspecific symptoms.