Pathophysiology of PH
Pathophysiology of idiopathic PH
At the level of the endothelium and vascular smooth muscle cells, the balance between vasodilating and vasoconstricting compounds is disturbed. The consequence is contraction of the smooth muscle cells and constriction of the capillary.
- The prostacyclin pathway - PGI2 is deficient in PH and levels of thromboxane (another vasoconstrictor) are increased. So, vasodilation by this pathway is decreased.
- The nitric oxide pathway - Patients with PH have decreased NO synthase (NOS) expression and thus lower levels of NO. The smooth muscle relaxing capacity of this pathway is diminished.
- The endothelin pathway - ET-1 is elevated in patients with PH. As a result, the vasoconstriction is increased. These pathophysiological processes result in thickening of the walls of the small lung arteries.