Pulmonary Hypertension

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What is Pulmonary Hypertension?

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Pulmonary hypertension means high blood pressure in the lung blood vessels. It is not a disease itself, but rather a final common pathway for many different diseases.

Pulmonary arterial hypertension is classified as pulmonary artery pressures higher than 30mmHg. It may affect the arteries or veins of the lungs. Pulmonary arteries take blood from the right side of the heart to the pulmonary capillaries; pulmonary veins transport the oxygenated blood from the capillaries to the left side of the heart.

The disease discussed below is pulmonary arterial hypertension. Pulmonary venous hypertension, usually arising due to left heart disease, is discussed under 'pulmonary oedema', though in chronic form it eventually causes pulmonary arterial hypertension.

Who gets Pulmonary Hypertension?

Primary pulmonary hypertension (ie. no obvious cause) is a rare disease. It is found in 0.1-0.2% of all patients at autopsy, but many are asymptomatic until late in the process.

Secondary pulmonary hypertension, however, is much more common that that - since it frequently complicates almost any form of chronic lung disease.

Predisposing Factors

Many diseases may cause pulmonary hypertension. These include:

Diseases of the lung blood vessels themselves (pulmonary embolisms),
Any chronic lung disease (especially COPD),
Musculoskeletal disorders (myasthenia gravis),
Left heart disorders (left ventricular failure, mitral stenosis),
Morbid obesity,
Obstructive sleep apnoea;

When none of these causes are present, "primary pulmonary hypertension" is diagnosed. It is a diagnosis of exclusion.

Progression

As mentioned above, pulmonary hypertension is a final common pathway for many different diseases. Thus, the early natural history of the pulmonary hypertension is disease such as pulmonary embolism or chronic lung disease. These diseases cause injury to the lung endothelial cells. These are the cells lining the blood vessels.

Endothelial damage causes a range of local effects, mediated by the release of enzymes and chemicals from these cells. These changes result in constriction of pulmonary blood vessels. In some cases, spasm of muscle layers inside blood vessels is also a factor; this means that treatment with vasodilator medication may be useful.

In the early stages of disease, these changes may only occur during exacerbations of underlying lung disease, for example, acute exacerbation of COPD. Eventually, however, pulmonary hypertension becomes severe and persistant. The strain on the right ventricle of the heart causes its function to decline, leading to right heart failure.

Lack of oxygen, caused by underlying lung disease, and abnormal blood flow through the lungs, further impairs the function of the right ventricle, and eventually leads to left ventricular failure, as well.

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