Blood circulation in the human body is managed by two sets of blood vessels - arteries that carry purified blood from the left side of the heart to the rest of the body and the veins that bring in blood from distant organs back to the right side. The first is known as systemic circulation and the latter is pulmonary circulation.
The right ventricle pumps venous blood from the heart to the arteries of the lungs for oxygenation, which is again pumped by the heart through the systemic circulatory system. Just as high blood pressure (hypertension) is elevation of pressure in the blood vessels of the systemic circulation, pulmonary hypertension is when the pressure in the pulmonary arteries is above normal.
Primary pulmonary hypertension is a rare disease with unknown causes while secondary pulmonary hypertension is a complicated condition caused by pulmonary, cardiac and extra-thoracic conditions. Pulmonary hypertension invariably precedes Cor pulmonale, an enlargement of the right ventricle of the heart. Chronic pulmonary hypertension, if not checked, ultimately leads to failure of the right ventricle.
Pulmonary hypertension can be logically or casually connected to excessive flow in the pulmonary arteries, for example, in left to right shunts due to congenital cardiac anomalies. Pulmonary hypertension occurs when pulmonary blood flow and pressure is more than what the pulmonary vessels can handle. Any condition that obstructs drainage of pulmonary venous blood including blockage by foreign matter or a blood clot can also potentially cause pulmonary hypertension.
Pulmonary venous hypertension
Pulmonary venous hypertension is caused by the failure of the left heart. This can occur due to stenosis or regurgitation of the mitral valve or the aorta. The malfunctioning heart is unable to pump efficiently and the blood does not leave the pulmonary circulation at the appropriate time. This causes abnormally high pressure in the pulmonary veins, which can be carried back to the pulmonary arteries.
Pulmonary arterial hypertension
Pulmonary arterial hypertension is associated with autoimmune diseases like HIV, scleroderma and cirrhosis, sickle cell disease and congenital heart disease. It can also develop due to genetic disorders.
Many high blood pressure medications like diuretics, ACE inhibitors and calcium channel blockers are used in the treatment of pulmonary venous hypertension as well. However, their benefits have not been established with surety. Vasoconstriction has traditionally been related to lifestyles. Therefore, the role natural remedies for high blood pressure play in the treatment of pulmonary hypertension needs to be explored further.
Pulmonary arterial hypertension is best treated with prostaglandins like prostacyclin and its derivatives. Endothelin receptor antagonists, phosphodiesterase type 5 inhibitors and vasoactive intestinal peptide inhalation are in different stages of clinical trials and some of them are expected to enter the market in 2008. Sildenafil, a selective inhibitor of specific phosphodiesterase was approved for the treatment of pulmonary arterial hypertension in 2005. Surgical procedures involve:
- Creating a connection between the right and left atriums to relieve pressure on the right side. This may cause a condition of hypoxia, reduction of oxygen level in the blood.
- A complicated operation for removing a blood clot.
- Lung transplantation, which cures the condition but is associated with complications associated with transplantation.
Primary pulmonary hypertension is extremely rare and occurs in about two persons per million per year. Prognosis is poor but is expected to improve once the effect of newer drug therapies, overall care and a better lead time (early diagnosis) is clearly established.