Pulmonary Hypertension

Pulmonary hypertension (PH) is a haemodynamic state, not a single disease. At rest, it is defined by a mean pulmonary arterial pressure (mPAP) greater than 20 mmHg, measured by right heart catheterisation (RHC). The pressure is harmful because the right ventricle (RV) is designed to pump against a low-resistance circuit. In pulmonary arterial hypertension (PAH), a Group 1 disorder, the small pulmonary arteries constrict and undergo intimal and medial proliferation, obstructive remodelling, and in-situ thrombosis. Pulmonary vascular resistance (PVR) rises. The thin-walled RV must generate progressively higher pressure, then dilates, becomes less efficient, and eventually fails. The usual mode of death in advanced PAH is progressive right-sided heart failure. The falling RV output explains exertional fatigue, reduced exercise tolerance, dizziness, and syncope. RV dilation can push the interventricular septum towards the left ventricle, limiting left-sided filling and further reducing cardiac output. The kidneys interpret the low forward flow as inadequate circulating volume, activating sodium and water retention; this is why venous congestion and oedema can worsen even while effective cardiac output falls. The presenting pattern is often subtle: exertional dyspnoea...