What is PAH?

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.¹

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: Click to enlarge

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 (< 15 mmHg).¹

In most cases the earliest symptom is Dyspnoea on physical exertion. Other symptoms include syncope or near syncope, fatigue and peripheral oedema.¹ Chest tightness and pain similar to angina may occur, particularly on physical exertion.

References
1. Gaine SP, Rubin LJ. Primary Pulmonary Hypertension. Lancet 1998; 352: 719−25.