Pressure helps blood flow through blood vessels. Hypertension occurs when this pressure gets too high. When this happens in the blood vessels in the lungs it is called pulmonary hypertension.

Normal pressure for blood flow through the lungs is one-sixth of the pressure for the rest of the body. Pressure may rise for any number of reasons. It creates a potentially serious condition. The right side of the heart needs to pump harder to move blood against the pressure. If left untreated the right side of the heart can eventually fail.

Pulmonary Circulation
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The blood vessels in the lungs are very sensitive to oxygen. The lower the level of oxygen, the narrower the vessels become. Higher pressure will be needed to push blood through the narrow blood vessels. Pressure will also increase when there is more blood in the lungs than normal.

The increase may be caused by:

  • Chronic obstructive pulmonary disease (COPD) is the most common cause. This condition causes destruction of lung tissue. This decreases the number of blood vessels. It also lowers the amount of oxygen available.
  • Heart abnormalities can result in extra blood in the lungs. Some are conditions people are born with. Others may develop over time. Some of these conditions are:
    • Septal defects (holes between the right and left sides of the heart, present at birth)
    • Tight (stenotic) or leaky heart valves
  • Lung diseases that scar the lungs:
    • Scleroderma (systemic sclerosis)—stiffen blood vessels, effectively preventing them from opening which raises the pressure
    • Patients who have large sections of lung removed surgically
    • Systemic lupus erythematous (SLE)
  • In obstructive sleep apnea breathing stops at times through the night. This lowers available oxygen. As a result, pulmonary blood pressure will also increase.
  • Muscle weakness can make it difficult to breathe. This will lower the available oxygen. This weakness is common in neuromuscular disorders such as:
  • Mountain climbers all develop the condition. It is the natural result of breathing thin air. This is one cause of high altitude sickness.
  • Pulmonary embolism is a build up of blood clots in the lungs. These clots plug up the blood vessels.
  • A type of chest wall deformity is known as pectus excavatum. Rarely, severe scarring of the chest wall, can prevent chest expansion. It has the same effect as scarring of the lungs themselves.
  • Idiopathic pulmonary arterial hypertension is due to defects in the arteries of the lungs. There is no known cause. It is likely due to genetic factors.

Other factors and conditions that can create pulmonary hypertension include:

  • Exposure to certain substances, such as cocaine and amphetamines
  • HIV infection
  • Liver disease