PH can be due to spasm of the pulmonary arteries (also known as vasoconstriction). Vasoconstriction narrows the pulmonary arteries, raising the blood pressure in the pulmonary arteries (higher pulmonary artery pressure = PAP).
- It used to be believed that many patients with PH (such as patients with IPAH) had PH because of vasoconstriction in their pulmonary arteries. It is because of this idea that many PH patients used to be treated with vasodilator medications (which relax pulmonary arteries) to reduce the blood pressure in the pulmonary arteries.
- However, it is now clear that in most patients with PH, vasoconstriction is not an important cause of PH. As such, vasodilator medications are not useful in treating PH in most patients.
Vasoconstriction of the pulmonary arteries happens when blood oxygen levels are low. Vasoconstriction is believed to cause some types of PH:
- WHO Group III PH: PH due to lung disease that causes low blood oxygen levels, such as emphysema of the lung or scarring (also known as fibrosis) of the lungs, or breathing problems during sleep (such as sleep apnea)
Patients who are seriously ill in the intensive care unit (ICU) or after major surgery can also develop PH due to vasoconstriction.