• Pulmonary hypertension is abnormally elevated pressure in the pulmonary circulation.
• The classification of primary and secondary pulmonary hypertension has been reclassified. It now is based on the primary underlying disease or condition, symptoms, and treatment options for pulmonary hypertension. There are five classes or groups in this new classification system.
• Pulmonary hypertension can have no identifiable cause and is referred to as idiopathic pulmonary hypertension (formerly called primary pulmonary hypertension).
• Pulmonary hypertension can be caused by certain drugs, diseases (scleroderma, dermatomyositis, systemic lupus), infections (HIV, schistosomiasis), liver disease, valvular heart disease, congenital heart disease, chronic obstructive lung disease (COPD), blood clots in the lungs, and persistent pulmonary hypertension of the newborn (PPHN).
• Risk factors for pulmonary hypertension are liver failure, chronic lung disease, blood clotting disorders, and underlying diseases, such as scleroderma, dermatomyositis, and systemic lupus erythematosus.
• Signs and symptoms of pulmonary hypertension include
○ shortness of breath,
○ difficulty breathing with exertion,
○ rapid breathing, and
○ rapid heart rate.
• Pulmonary hypertension is diagnosed by measuring the pulmonary pressures by either ultrasound of the heart (echocardiogram) or right heart catheterization.
• The treatment for pulmonary hypertension can include oxygen, diuretics, blood thinners, medications that open the pulmonary arteries, and treatments for any underlying disease.
• The prognosis and life expectancy for a person with pulmonary hypertension are improving as newer treatment options become available; however, the prognosis may depend on the underlying disease or condition.
Pulmonary hypertension occurs when the pressure in the pulmonary arteries increases abnormally. To help explain this condition further, here is how the pulmonary arteries work.
The human body has two significant blood vessels that distribute blood from the heart to the body. One set pumps blood from the right heart to the lungs, and the other from the left heart to the rest of the body (systemic circulation). When a doctor or a nurse measures the blood pressure on a person’s arm, he/she measures the pressures in the systemic circulation. When these pressures are abnormally high, they are diagnosed with high blood pressure (systemic hypertension).
The portion of the circulation that distributes the blood from the right side of the heart to the lungs and back to the heart’s left side is referred to as the pulmonary (lung) circulation.
The right ventricle pumps the blood returning from the body into the pulmonary arteries to the lungs to receive oxygen. The pressures in the lung arteries (pulmonary arteries) usually are significantly lower than the pressures in the systemic circulation. When the pressure in the pulmonary circulation becomes abnormally elevated, it is referred to as pulmonary hypertension. This most commonly occurs when the pulmonary venous pressure is elevated, so-called pulmonary venous hypertension (PVH). This pressure is transmitted back to the right side of the heart and the pulmonary arteries. The result is elevated pulmonary pressure throughout the pulmonary circulation. Some of this is a direct pressure transmission from the venous system backward. Some can result from a reactive constriction of the pulmonary arteries.
Less commonly, pulmonary hypertension results from constriction or stiffening of the pulmonary arteries that supply blood to the lungs, so-called pulmonary arterial hypertension (PAH).
Whether it is pulmonary venous or pulmonary arterial hypertension, it becomes more difficult for the heart to pump blood forward through the lungs. This stress on the heart leads to enlargement of the right heart, and eventually, fluid can build up in the liver and other tissues, such as in the legs.
Normal Pulmonary Artery Pressure Range
When the heart pumps blood, it is referred to as systole, and when the heart fills with blood, it is referred to as diastole. Normal pulmonary artery pressures range from an upper pressure (systolic) of 15-30 mmHg and lower pressure (diastolic) of 4-12 mmHg. These values can be obtained approximately by an ultrasound of the heart (echocardiogram), and more accurately using a catheter to measure the pulmonary circulation pressures (right heart catheterization).
Shortness of breath, or difficulty breathing, is referred to medically as dyspnea. There are many causes of shortness of breath. Sometimes a person may have other symptoms with shortness of breath, for example:
• Bloody sputum
• Neck pain
• Chest pain
• Feeling anxious
• Fainting (syncope)
• Pain with inhalation
There are many causes of pulmonary hypertension. Often more than one mechanism is involved in a specific disease process.
This can also change as the disease progresses.
1. Diseases that affect the flow out of the heart to the rest of the body result in backflow of blood (stacking of blood) that raises pulmonary venous pressures leading to pulmonary hypertension.
2. Hypoxic pulmonary vasoconstriction is when the lung vessels narrow to divert blood from poorly functioning segments of the lung. For instance, when pneumonia develops, a portion of the lung becomes inflamed. It works poorly in performing the lung functions (to add oxygen and remove carbon dioxide from the blood). This process diverts blood from these poorly working areas and sends it to better functioning lung tissue. However, a problem develops when all the blood has a low oxygen level (hypoxia). This causes constriction of the vessels on the pulmonary arterial side and hence raises the pressure.
3. Remodeling of blood vessels also occurs in some diseases whereby the vessel’s inner lining (lumen) becomes narrowed due to inappropriate growth of the tissue within and around the vessel. Masses and scarring from other diseases can compress and narrow vessels causing increased resistance to flow, resulting in elevated pressures.
4. In a fairly common parasitic infection in the Middle East (schistosomiasis), the lung vessels’ blood vessels become blocked by the parasites causing pulmonary artery hypertension.
5. Some substances cause constriction of the blood vessels. Pulmonary hypertension has been rarely reported using anti-obesity drugs, such as dexfenfluramine (Redux) and Fen/Phen. These medications have seen been removed from the market. Some street drugs, such as cocaine and methamphetamines, can cause severe pulmonary hypertension.
6. Some diseases raise pulmonary pressures to cause pulmonary artery hypertension for unclear reasons. Perhaps an unknown toxin or chemical affects the blood vessels by causing constriction or inappropriate tissue growth within or around the vessel. For example, there is a condition known as portopulmonary hypertension that is a result of liver failure. When these individuals receive a liver transplant, pulmonary hypertension disappears, suggesting that the failing liver cannot clear some biochemical that leads to pulmonary artery hypertension.
Idiopathic Pulmonary Hypertension Causes
Primary pulmonary hypertension has no identifiable underlying cause. This term is mainly a historical name and is no longer used. The current term used to describe this condition is idiopathic pulmonary hypertension. Idiopathic pulmonary hypertension is more common in young people and more common in females than males.
Idiopathic pulmonary hypertension unusually is an aggressive and often fatal form of pulmonary hypertension. Whereas it is known that the arterial obstruction is caused by a building up of the smooth muscle cells that line the arteries, the underlying cause of the disease has long been a mystery.
A genetic cause of the familial form of idiopathic pulmonary hypertension, now referred to as Heritable PAH, has been discovered. Mutations in a gene called BMPR2 cause it. BMPR2 encodes a receptor (a transforming growth factor-beta type II receptor) that sits on the cells’ surface and binds the TGF-beta superfamily molecules. Binding triggers conformational changes that are shunted down into the cell’s interior. A series of biochemical reactions occur, ultimately affecting the cell’s behavior. The mutations block this process. This discovery may provide a means of genetic diagnosis and a potential target for the therapy of people with familial (and possibly also sporadic) primary pulmonary hypertension.
Many people with pulmonary hypertension may have no symptoms at all, especially if the disease is mild or in the early stages.
Pulmonary hypertension symptoms may include:
1. Shortness of breath that worsens with activity
2. Other common complaints are cough, fatigue, dizziness, and lethargy.
3. With the advancement of the condition and ensuing right heart failure, shortness of breath may become worse. Retention of fluid in the body may increase (due to failure of the heart to pump blood forward), resulting in swelling in the legs.
4. People may also complain of chest pain and angina.
5. Depending on the underlying associated disease, pulmonary artery hypertension can have other manifestations. For example, characteristic skin changes were seen in scleroderma or liver disease signs seen in portopulmonary hypertension.
Signs of pulmonary hypertension may include:
1. Rapid breathing, hypoxia (low oxygen level in the blood), and swelling in the legs.
2. In severe pulmonary hypertension, the health care professional may hear louder than normal components of heart sounds when he or she listens to the heart with a stethoscope (auscultation).
3. The doctor may also feel elevation of the chest wall when the heart pumps. This may indicate enlargement of the heart’s right side, suggestive of pulmonary hypertension (right ventricular heave).
The conventional classification, primary (idiopathic) and secondary pulmonary hypertension, called pulmonary arterial hypertension, has been reclassified and is now based on the leading underlying cause, characteristics, and pulmonary hypertension treatments. These terms were updated in 2013. This system classifies the condition based on five classes.
Class 1 includes:
Pulmonary arterial hypertension including idiopathic, previously referred to as primary pulmonary arterial hypertension), inherited pulmonary arterial hypertension, drug-induced pulmonary arterial hypertension.
Pulmonary arterial hypertension associated with the following:
• Connective tissue diseases like systemic lupus erythematosus or scleroderma
• Liver disease (elevated pressures in the liver, portal hypertension);
• Congenital heart disease
• Schistosomiasis (a parasite infection that can clog the pulmonary arteries)
• Pulmonary venous-occlusive disease (sporadic)
• Persistent pulmonary hypertension of the newborn
Class 2 includes:
Pulmonary hypertension due to left heart disease:
• An elevation of pulmonary arterial pressure because of increased pulmonary venous pressure backing up into the lungs
• Heart failure due to left ventricular systolic or diastolic dysfunction
• Valvular heart disease
• Some congenital/acquired heart diseases
Class 3 includes:
Pulmonary hypertension due to lung diseases and or hypoxia (low oxygen levels). This includes:
• Chronic obstructive lung disease (COPD)
• Interstitial lung diseases
• Sleep apnea
• Chronic exposure to high altitudes
• Congenital lung disease
Class 4 includes:
Chronic thromboembolic pulmonary hypertension (chronic blood clots to the lungs that don’t dissolve, also termed CTEPH).
Class 5 includes:
Pulmonary hypertension with unclear multifactorial mechanisms, for example:
• Blood disorders (including hemolytic anemias)
• Systemic disorders (such as sarcoid)
• Metabolic disorders where cellular chemistry is abnormal (such as glycogen storage diseases)
• Tumors, fibrosis, and other problems obstructing blood flow through the lungs
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