Pulmonary Arterial Hypertension

Abstract

Pulmonary hypertension is usually classified as primary (idiopathic) or secondary.1 It is now clear, however, that there are conditions within the category of secondary pulmonary hypertension that resemble primary pulmonary hypertension in their histopathological features and their response to treatment. For this reason, the World Health Organization (WHO) classified pulmonary hypertension into five groups on the basis of mechanisms, rather than associated conditions. In 2003, the World Health Organization revised the classification of PAH into 5 categories based in part on etiology: pulmonary arterial hypertension, pulmonary venous hypertension, pulmonary hypertension associated with hypoxemia, pulmonary hypertension resulting from chronic thrombotic or embolic disease, and miscellaneous. 2 Group I of the WHO classification, designated pulmonary arterial hypertension, is the principal focus of this review. Pulmonary arterial hypertension is defined as a sustained elevation of pulmonary arterial pressure to more than 25 mm Hg at rest or to more than 30 mm Hg with exercise, with a mean pulmonary-capillary wedge pressure and left ventricular end-diastolic pressure of less than 15 mm Hg.3Diagnosis of PPH one must excludes all secondary cause of PHT and demonstrate normal pulmonary wedge pressure. 2,3 Pathophysiology: The histopathology of pulmonary vascular disease has been classified in two phases, early description in the 1950s (the Heath- Edwards classification) and an extension of this by Rabinovitch et al. 2.3Although pulmonary vascular resistance( PVR = mPAP _ mPCWP/Q p) may be as high as 8-10 Wood units immediately after birth, it normally falls rapidly through the first week of life. By 6-8 weeks, pulmonary vascular resistance usually has reached a normal adult level of 1-3 Wood units. In an infant, although the pulmonary pressure is at systemic levels, the pulmonary vascular resistance is low and there is pulmonary over circulation. 2.3,23,26,28 Frequency data are difficult to confirm, as there are no international registries tracking the incidence and prevalence of pulmonary hypertension. Elevated pulmonary artery pressure in congenital heart disease is caused by pulmonary over circulation, pulmonary vasoconstriction, and pulmonary vascular disease, either alone or in combination.