Pulmonary hypertension is caused due to vasoconstriction of blood vessels of the lungs that cause difficulty in pumping blood from the heart to lungs leading to difficulty in exchange of gases. The workload on heart increases and heart has to work harder to pump blood through narrowed vessels of lungs. This leads to weakening of heart muscles with time and less supply of oxygenated blood to different tissues and organs.
Types of Pulmonary Hypertension
WHO in 2003 put forward a classification for pulmonary hypertension ranging from group 1 to group 5. Group 1 relates to numerous causes including connective tissue diseases (autoimmune diseases), liver diseases, congenital heart diseases, sickle cell anemia, HIV infection, schistosomiasis (parasitic infection), due to drugs and certain toxins (include some of diet pills and recreational drugs) and diseases affecting small blood vessels of the lungs. This group also includes idiopathic pulmonary hypertension that has no known cause.
Group 2 pulmonary hypertension is caused by conditions affecting left side of the heart including mitral valve disease and chronic systemic elevated blood pressure. Group 3 PH relates to hypoxic conditions and various breathing and lung conditions such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (interstitial lung diseases) and sleep apnea. Group 4 PH is associated with clotting disorders such as blood clots in the lungs (pulmonary embolism). Group 5 pulmonary hypertension is a miscellaneous category such as blood disorders (polycythemia vera and thrombocythemia), metabolic disorders including thyroid diseases and glycogen storage disease, systemic disorders (such as sarcoidosis and vasculitis), kidney diseases and other conditions including tumors causing compression of pulmonary arteries.
What is the Drug of choice for Pulmonary Hypertension?
The drug of choice for pulmonary hypertension depends on the group of PH and the underlying cause of it. Pulmonary hypertension is a progressive disease, which is life threatening if left untreated with a survival rate of only 2-3 years in the absence of management. There have been advances in treatment modalities with rise in survival rate to 5-10 years and more medications in the market. Unfortunately, there is no definitive cure for pulmonary hypertension. The aim of treatment is focused on slowing the progression of disease by improving the quality of life of patient with medications and lifestyle modifications.
There are various treatment options approved by US FDA (Food and Drug Administration) which include prostacyclin analogues (also known as vasodilators) that reduce blood pressure by relaxation of pulmonary blood vessels. The relaxation of blood vessels cause increase in blood flow to the lungs, thus reducing workload on heart. The prostacyclin used in treprostinil, which can be taken orally (Orenitram), inhaled (Tyvaso and iloprost), IV (Remodulin), and subcutaneously and also Flolan (epoprostenol) is used as a vasodilator.
Endothelin Receptor Antagonists (ERAs) are group of medications that prevent vasoconstriction. They are usually taken orally and the various ERAs used are ambrisentan (Letairis), macitentan (Opsumit) and bosentan (Tracleer).
Phosphodiesterase-5 inhibitors (PDE 5 inhibitors help lungs in making natural vasodilators by augmentation of cGMP and NO. PDE 5 inhibitors used are sildenafil (Revatio) and tadalafil (Adcirca) in oral form.
Soluble Guanylate Cyclase (sGC) relaxes pulmonary blood vessels by increasing interaction of sGC with NO. Example includes riociguat (Adempas).
Selective IP Receptor Agonist helps in relaxing blood vessels in the lungs by activating prostacyclin receptor. The example is selexipag (Uptravi) taken orally.
Conventional therapies for pulmonary hypertension include calcium channel blockers (such as nifedipine and diltiazem). Anticoagulants are used in the form of warfarin (Coumadin), heparin, fondaparinux and argatroban to prevent blood from clotting. Digoxin relieves symptoms of heart failure by slowing and strengthening heart beats. Diuretics help in removing extra fluid buildup from the body reducing swelling. Patients who have difficulty breathing can also be put on artificial oxygen if needed.
In severe cases of pulmonary hypertension, along with medications surgeries such as lung transplant, atrial septostomy, or heart-lung transplant may be recommended.
Patient is also advised lifestyle modification and all the above treatments help prolong survival rate of pulmonary hypertension patients.
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