Pathophysiology of pulmonary hypertension

Pulmonary hypertension is not a disease, per se, but a hemodynamic abnormality that is common to a variety of conditions. The primary pulmonary hypertension (PPH) Registry initiated by the National Heart, Lung and Blood Institute in 1981 defined pulmonary hypertension as a mean pulmonary arterial pressure (PAP) greater than 25 mm Hg at rest or 30 mm Hg on exercise (1). It should be recognized, however, that PAP varies with age. Between days 1 and 3 of neonatal life the mean PAP falls, from 6 to 45 years of age it remains fairly constant, and it increases beyond 60 to 83 years of age. Consequently, the mean plus 2 SD gives an upper limit of normal of 20 mm Hg from childhood to approximately 60 years of age. The upper limit for pulmonary vascular resistance (PVR) index [(PAP wedge pressure)/cardiac index] in normal subjects increases from approximately 2.8 (610 years) to 3.2 (32 to 45 years) to 4.6 mm Hg/L/min/m2 (60-83 years).