Pulmonary arterial hypertension (PAH) is a syndrome characterised by a progressive increase in pulmonary vascular resistance leading to right ventricular overload and eventually to right ventricular failure and premature death.
The increase in pulmonary vascular resistance is related to a number of progressive changes in the pulmonary arterioles, including:
Vasoconstriction
obstructive remodelling of the pulmonary vessel wall through proliferation in the various layers of the blood vessel wall (smooth muscle cell and endothelial cell proliferation)
inflammation
in-situ thrombosis.
The main histological features include medial Hypertrophy, intimal thickening, adventitial thickening, plexiform lesions and in-situ thrombosis (Figure 1). The plexifom lesion represents a focal proliferation of endothelial and smooth muscle cells and is pathognomonic of Pulmonary Arterial Hypertension (PAH).
Figure 1
Pulmonary Arterial Hypertension (PAH) is defined as a sustained elevation of mean pulmonary arterial pressure to more than 25 mmHg at rest or to more than 30 mmHg while exercising, with a normal pulmonary wedge pressure.
In most cases the earliest symptom is Dyspnoea on physical exertion. Other symptoms include syncope or near syncope, fatigue and peripheral oedema. Chest tightness and pain similar to angina may occur, particularly on physical exertion.