This episode explores pulmonary arterial hypertension (PAH) as a disease of misplaced resistance. The pulmonary circulation is designed for flow, not force; when vascular tone and remodelling raise pressure, the right ventricle is pushed beyond its physiological design. We examine PAH therapies as targeted attempts to reopen pathways, rebalance signalling, and protect the right heart—often using mechanisms distinct from systemic hypertension.

Key takeaways you’ll build and reuse throughout the series:

* Pulmonary circulation as a unique system: low pressure, high compliance, and vulnerability to small increases in resistance.

* Pathogenic signalling pathways: endothelin excess, nitric oxide deficiency, and prostacyclin loss as drivers of disease.

* Targeted drug classes: endothelin receptor antagonists, phosphodiesterase-5 inhibitors, soluble guanylate cyclase stimulators, and prostacyclin analogues.

* Right ventricular perspective: why symptom burden and prognosis depend as much on ventricular adaptation as vascular change.

* Clinical realism: combination therapy, gradual escalation, and the limits of pharmacology in advanced disease.

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