Phase 1 · Understand the Body — Why the disease behaves the way it does.
The One-Line Truth
The whole disease in one chain
Everything on this page exists to explain this line.
Five types by cause: blood vessel wall thickening (type 1), left heart backup (type 2), lung disease (type 3), clot blockage (type 4), or mixed (type 5) — all raise pressure in the lung arteries and wear out the right heart.
Garden hose backing up with kinks
Imagine a garden hose carrying water from a pump (the right ventricle) through narrow, kinked sections (the stiffened lung arteries) to spray onto a garden (your lungs). Normally the hose is wide and flexible, so water flows easily at low pressure. But if the hose walls thicken, kink, or clog with debris (mimicking the five types of PH: wall thickening like type 1, backup from the garden bed being flooded like type 2, the soil choking the roots like type 3, stones blocking the line like type 4, or multiple problems together like type 5), pressure builds upstream. The pump now has to squeeze impossibly hard every second to push water through. At first the pump muscle bulges and strains (hypertrophy), but eventually it stretches and weakens (dilation and failure), can no longer move water forward, and water backs up into the pump inlet pipe (the right atrium and body veins). The gardener (you) feels tired and short of breath because less water reaches the leaves (your muscles and brain need less oxygen), and if the pump completely fails, the system collapses into shock.
ESC/ERS Guidelines for Pulmonary Hypertension 2022 · AHA/ACC Pulmonary Hypertension Scientific Statement · Chest (Journal of the American College of Chest Physicians) · World Health Organization Pulmonary Hypertension Classification · reviewed 2026-07-07