What is pulmonary hypertension? What causes high blood pressure in the lungs?

Date: Feb-11-2014Pulmonary hypertension is high blood pressure in the blood vessels that collect oxygen from the lungs.

The oxygenated blood is supplied to the rest of the body via the relevant pumping chamber of the heart. Hypertension in this respiratory loop of our circulation is a progressive and serious condition.

Pulmonary hypertension is not related to general hypertension, which is a separate condition of systemic high blood pressure, which affects the wider circulatory system and is measured using an arm cuff.

Whereas the systemic condition of raised blood pressure can often be prevented, pulmonary hypertension often has genetic factors.

This page will explain the causes behind raised blood pressure in the blood vessels of the lung, and the symptoms produced by this localized hypertension. Here is also an outline of the management options in the treatment of the condition.

What is pulmonary hypertension?

The lungs are made up of tiny air sacs (alveoli), each bringing oxygen into contact with tiny blood vessels that go straight back to the heart.

The definition of pulmonary hypertension is straightforward: it is an abnormally raised blood pressure in the blood vessels that go to the lungs and return oxygenated blood to the heart and, from there, to the rest of the body.

Pulmonary hypertension is diagnosed when resting pressure in the pulmonary artery is more than 25 mmHg, and more than 30 mmHg during exercise.1,2 (Normal pulmonary artery pressure at rest is within the range of 8 mmHg and 25 mmHg, and typically around 14 mmHg.)1,3

There are two types of raised blood pressure in the lungs - primary and secondary. Primary pulmonary hypertension is a relatively rare, standalone condition, whereas secondary pulmonary hypertension is caused by an underlying condition - hence, secondary to it - such as a heart defect.1

What causes pulmonary hypertension?

Just as the narrowing of a garden hosepipe will increase the pressure of the flow and cause water to back up, a similar effect gives rise to pulmonary hypertension.

The walls of the blood vessels in the lung thicken, narrowing the lumen that blood can travel through and increasing the pressure.4

The back pressure on the heart, the increased effort needed to maintain the blood flow, leads to a disease in the heart known as right ventricular hypertrophy. This is life-threatening because it can lead to right heart failure, which is behind most deaths of people with pulmonary hypertension,5 underlining the importance of its diagnosis and treatment.

Why the blood vessels in the lungs thicken in pulmonary hypertension has a complex answer - numerous factors can be involved, including: genetics, clotting, inflammation and changes in metabolism.4

Chest doctors (cardiothoracic specialists) have collected dozens of pulmonary hypertension syndromes into five clinical groups:3,6,7

Pulmonary arterial hypertension, a group that includes these causes:

- idiopathic or unknown

- connective tissue causes such as sclerosis

- heart defects present at birth (congenital)

- inherited genetic causes (BMPR2 gene mutation, for example)

- associated with drugs, toxins or HIV infection.

- pulmonary veno-occlusive disease, sometimes associated with cancer or cancer treatment8

Left heart disease (heart valve disease, for example)

Lung disease (COPD and chronic high-altitude exposure are examples)

Chronic thrombo-embolic pulmonary hypertension (after a blood clot that has reached the lung)

Miscellaneous, multifactorial, or unclear causes (numerous diagnoses are included in this group).

What are the symptoms of pulmonary hypertension?

The major symptom of pulmonary hypertension that is experienced by the majority of patients is shortness of breath (breathlessness or dyspnea).1,2,9

In addition to breathlessness, two other symptoms are also key indicators of pulmonary hypertension:

Fatigue or tiredness

Syncope or fainting/dizziness.

The major symptom of pulmonary hypertension is breathlessness - it is one of the factors affecting the distance patients can walk.

A picture of these main symptoms and their effect on quality of life is given by the way they are tested in clinical trials of drugs used to treat pulmonary hypertension, in a measure of exercise capacity called the 6-minute walk distance.10,11

An improvement in the distance that patients can walk in a 6-minute timeframe before breathlessness, fatigue, chest pain, or near syncope become intolerable is the measure by which drugs have been shown to be effective against pulmonary hypertension.

It is also a measure by which pulmonary hypertension can be staged from class 1 (pulmonary hypertension without any exercise limitation) to class 4 (where discomfort is felt even at rest, without physical exertion). This staging is used as an indication of the prognosis or outlook of the condition.2

How is pulmonary hypertension treated?

The precise treatment program that is appropriate for an individual person with pulmonary hypertension depends on the underlying cause and factors such as severity and coexistence of other conditions. There is, however, a number of therapies that may be appropriate to the management of any case of high blood pressure in the lungs, including:3,12

Diuretics - 'water pills' to reduce fluid retention and so swelling, in the ankles and feet, for example

Exercise - low levels of anaerobic exercise such as walking, have been proven to be safe and to improve capacity for physical activities

Oxygen therapy - continuous oxygen helps to maintain oxygen saturation in the blood, and this is the mainstay of treatment for patients whose pulmonary hypertension has a lung disease cause (that is, they fall into group 3 above). The therapy is also administered to patients who are to be exposed to low oxygen levels, such as in high-altitude flights

Digoxin - this is a heart failure drug that helps control heart rate and rhythm and increases the amount of blood pumped by each heartbeat

Blood-thinning drugs (anticoagulation therapy) - warfarin is used for the prevention of blood clots, which are more likely because of the hypertension's effects on blood flow, the right side of the heart, and on activity levels.

Other medical treatments may be prescribed by doctors to meet the specific individual needs of advanced cases of pulmonary hypertension.3

A number of different drugs are used, sometimes in combination, from the following classes of medicine:

Calcium-channel blockers, including nifedipine, diltiazem, or amlodipine - for patients who have a positive vaso-reactivity test in response to these drugs (measured with the right heart catheterization procedure)

PDE5 (phosphodiesterase-5) inhibitors, which increase blood flow by widening blood vessels (by causing vasodilation). Viagra (sildenafil) is one of the PDE5 inhibitors used (widely known for its effect on blood flow to the aroused penis)
Prostanoids, such as epoprostenol, treprostinil, and iloprost - these are also vasodilator drugs with other effects

Endothelin receptor antagonists, such as bosentan and ambrisentan (also sitaxsentan in some countries) - these limit the vasoconstrictive effects of an excess of a natural peptide.

The last considered options for selected patients with advanced disease due to pulmonary hypertension are transplant surgeries and other invasive procedures.

The procedures used are:3,12

Atrial septostomy, a procedure to introduce a shunt between heart chambers and improve cardiac output while patients await transplant surgery

Lung transplant - one or both lungs replaced by donation from a deceased person

Combined heart and lung transplant.

Some patients with the chronic thromboembolic type of pulmonary hypertension may be eligible for a procedure called pulmonary thromboendarterectomy.3 Also known by its abbreviation PTE, it is specialized heart surgery to remove blood clots from coronary arteries.

Written by Markus MacGill

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