Article Sections

Introduction

Pulmonary hypertension (PH) refers to approximately 50 conditions that increase pulmonary artery pressure (PAP), with a common final pathway of progressive right ventricular failure, carrying high morbidity and mortality.  The formal definition of PH (which has evolved over time) is a mean PAP ≥20 mm Hg.

Pathophysiology

Normally, the pulmonary circulation (ie, vessels from the pulmonic valve to the left atrium) is a low-pressure system, flowing at ~1/6th of systemic pressures.  The low pressure is made possible by highly compliant, distensible pulmonary vessels.  PH involves several mechanisms:

  • Vasoconstriction:  Pulmonary endothelial dysfunction leads to imbalance between endogenous vasoconstrictors (↑ endothelin-1) and vasodilators (↓ nitric oxide and prostacyclin)
  • Vascular remodeling:  Smooth muscle cell proliferation, neointimal hyperplasia, extracellular matrix deposition, inflammatory cell infiltration, and microthrombosis in situ

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