Pulmonary hypertension (PH) is a severe health condition in which the mean pulmonary arterial pressure increases to 25 mmHg or more, even when the body is at rest. This high pressure in the blood vessels that transport blood from the heart to the lungs can cause various symptoms, including shortness of breath, can lead to right heart failure, and significantly affect the overall quality of life.

There are various classifications for PH, each relating to different underlying causes and also based on different treatment approaches and prognoses. PH is divided into five major groups, including PH due to left heart disease, PH resulting from lung diseases or hypoxia, chronic thromboembolic PH (caused by blood clots in the lungs), PH with unclear or multifactorial mechanisms, and pulmonary arterial hypertension (PAH).

PAH, in particular, is a rare but fatal form of PH. It results in vascular changes in small arteries and arterioles, increasing pulmonary arterial pressure and vascular resistance. The key mechanisms involved in PAH include structural changes in the lung blood vessel, narrowing of the blood vessels or pulmonary vasoconstriction, in situ thrombosis (clotting within the blood vessels), and stiffening of the pulmonary vascular wall.

Various bodily substances known as vasoactive mediators play a role in these processes. For example, nitric oxide (NO) and prostacyclin help to promote pulmonary vasodilation (widening of the blood vessels), which can alleviate PH. On the other hand, vasoconstrictors like endothelin-1 (ET-1) contribute to vasoconstriction and the proliferation of smooth muscle cells, potentially worsening PH.

The symptoms of PH can vary but typically include dyspnea (shortness of breath), fatigue, chest pain, and syncope (fainting or near-fainting spells). These symptoms often worsen over time, limiting the patient's ability to perform routine activities.

Despite the seriousness of PH, there are potential therapeutic options available. Treatments aim to lower the pressure in the lungs' arteries and prevent further damage. These include stimulators of cGMP signaling, nitric oxide, membrane receptor antagonists and agonists, and ion channel inhibitors. However, the treatment choice depends on the type of PH, its severity, and the patient's overall health.