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Pulmonary hypertension is characterized by high blood pressure (hypertension) in the pulmonary arteries that supply oxygen-poor blood to the lungs. There are a number of reasons this condition may result. For example, the blood vessels of the lung (pulmonary arterioles) may have narrowed, thus restricting blood flow through the lungs. Alternatively, the condition may be caused by heart disease of the left side of the heart, which causes blood to back up into the lungs, raising the blood volume in the pulmonary vascular bed.
Pulmonary hypertension is diagnosed by measuring the blood pressure in the pulmonary arteries. Under normal circumstances, mean pulmonary artery pressure at rest is about 14 mmHg (milimeters of mercury). Pulmonary hypertension is defined as a pulmonary artery blood pressure that is greater than 25 mmHg at rest or 30 mmHg during exercise. It is further classified by its underlying cause. Primary pulmonary hypertension (PPH) occurs with no known cause, whereas secondary pulmonary hypertension is due to another, identifiable factor.
Although PPH is rare, an estimated 500 to 1,000 new cases are diagnosed annually. The disease can occur in men, women and children of all ages. However, it is most common in females between 20 and 40 years old, with twice as many cases reported in women than men, according to the National Heart, Lung and Blood Institute. The condition is rare in children but is sometimes seen in infants who are born with a heart defect (congenital heart disease).
Secondary pulmonary hypertension (SPH), in which the high blood pressure is caused by another underlying condition, is much more common. Typical causes of SPH include:
- Lung disease (e.g., chronic obstructive pulmonary disease [COPD] and lung fibrosis). COPD is the most common cause of SPH in adults.
- Sleep apnea. This condition occurs when the upper airway becomes obstructed during sleep, resulting in poor oxygen flow. Untreated, this condition can lead to pulmonary hypertension. It is also associated with increased risk of cardiovascular disease.
- Heart problem (e.g., congenital heart disease or mitral valve stenosis). An abnormally functioning left ventricle can also cause pulmonary hypertension. Other heart problems associated with pulmonary hypertension include heart failure, certain cardiomyopathies, constrictive pericarditis, or left-to-right shunts such as those caused by a ventricular septal defect.
- Systemic connective tissue disease. These disorders are characterized by abnormalities in the connective tissue that provides structure to the body. Examples of this kind of disease are scleroderma and rheumatoid arthritis. Scleroderma is closely associated with Raynaud's phenomenon.
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Neuromuscular diseases that affect the respiratory muscles, causing them to function abnormally and reducing the lung's ability to receive oxygen. Examples of such diseases include poliomyelitis, myasthenia gravis and amyotrophic lateral sclerosis (Lou Gehrig's disease).
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Pulmonary embolism (a blood clot that has become lodged in a blood vessel in the lung).
Studies have shown that both primary and secondary pulmonary hypertension are linked to certain impaired genes. Both types can lead to serious cardiovascular problems if untreated.
The ability to cure pulmonary hypertension is related to the cause of the disease. There is no cure for primary hypertension, but in recent years, physicians have developed a number of approaches that can successfully manage the condition and improve the patient’s quality of life. Secondary pulmonary hypertension may be cured by treatment of the underlying condition. In either case, it is important to identify the condition as quickly as possible and seek out qualified treatment before permanent damage results to the lungs or the right side of the heart.
When pulmonary artery pressure becomes elevated, the right side of the heart has a harder time pumping blood through the narrowed pulmonary artery and to the lungs. Eventually, the continuous effort can cause the heart to become enlarged and weakened. Untreated pulmonary hypertension can lead to:
- Regurgitation of the tricuspid valve. A leaking valve on the right side of the heart.
- Cor pulmonale. Right-side heart failure.
It has also been shown that pulmonary hypertension increases the risks associated with some heart diseases. For example, individuals with myocarditis have significantly higher risks of mortality for each 5 mmHg increase in pulmonary blood pressure. In addition, these patients may be at a higher risk for endocarditis, which is an infection of the heart valves. To reduce the risk of endocarditis, some patients with pulmonary hypertension may be instructed to take antibiotics prior to dental procedures. | 
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