The Background to understanding Deep Vein Thrombosis

By Dr. J I Broch MBChB BSc (hons)

In order to appreciate a specific product like Airtight International ‘Travel Socks’, it is important to understand the basics of what DVT is and how the product works. This Section will outline the basic principles and fundamental biology involved.

• Blood is pumped around the body by the left side of the heart.

• It makes it way around the body via arteries and veins.

• It then returns to the right side of the heart, from where it is pumped through the lungs.

• From the lungs it passes back to the left side of the heart, to restart the cycle.

• Blood must pass through the lungs whenever it circulates the body.

The high pressure in the arteries due to the heart contracting maintains blood flow around the body.

However, The return of blood from the legs has two obstacles:

There is no pressure or pump to move blood upwards and gravity acts to keep blood in legs

The body overcomes this problem by the action of calf muscles and valves.

As blood passes up the veins, backflow is prevented by valves. Therefore, blood flow is one way.

Whilst walking around or during calf muscle activity, the veins are compressed forcing blood up the legs.

What is Deep Vein Thrombosis (DVT)?

’Thrombosis’ means blood clot. A DVT is a blood clot, which forms in the deep veins of the leg.

The blood clot (or thrombus) can form in the veins deep in these areas, and the clot then blocks the flow of blood and causes swelling and inflammation. In the most serious cases, a blood clot from the leg breaks off and travels through the bloodstream. The moving clot is called an embolus, and it can lodge in the lungs, brain, or heart and cause serious damage.

Symptoms can vary: • None • Swollen Leg • Pain

DVT may take some time to show itself, or it may even remain symptomless. They can, however, extend up the leg veins.

Deep Vein Thrombosis can lead to Complications. Part of the clot can break away from the wall of the vein. When this moves to a small vessel it will obstruct blood flow; this is called an embolism.

As blood passes through the lungs every time it circulates, the clot is likely to end up in the lungs; a Pulmonary Embolism.

Pulmonary Embolism is rare, however DVT causes other complications in many sufferers, including Skin Deterioration, Venous Ulceration, Physical Disability & Risk of future DVT.

Pulmonary Embolism

The lungs are very important for ensuring oxygen gets in to the body.

For this to occur:
* The lung surface must be healthy.
* Blood flow through the lungs must be maintained.

When clot is deposited in the lung vessels (PE), it will stop blood flow and have the effect of causing damage to the lung surface.

A small clot has the potential to be lethal. Pulmonary Embolism may occur weeks after the development of even a silent Deep Vein Thrombosis.

Risk Factors

There are 3 factors that are thought to be involved in the development of Deep Vein Thrombosis:

* Poor blood circulation / stagnation – reduced movement of calves

* Increased clotting potential – cabin environment

* Abnormal / altered blood vessel. – cabin environment

Any of the above will result in an increased risk of DVT in an otherwise healthy individual.

Other identified Risk Factors

*Age > 40

* Pregnancy

* Malignant disease

* Blood disorders
(maybe >20% people suffer from these)

* Cardiovascular disease

*Previous history of DVT / Pulmonary Embolism

* Recent Surgery

* Oestrogen (eg the Pill)

* Reduced mobility

* Not drinking enough fluids

Issues in Air Travel

There are a number of factors in airline travel that are thought to predispose to a condition in legs when a DVT may form:

LOW CONCENTRATIONS OF OXYGEN AND REDUCED PRESSURE

The Aircraft cabin creates a low-pressure, low oxygen environment, which has two effects:
• Leg veins expand and therefore blood velocity is reduced (think of hosing down the garden: if you squeeze the hosepipe, the water comes out quicker. The exact opposite is happening here)
• There is an increased tendency of blood to clot.

DEHYDRATION

Passengers who experience dehydration will have a reduced blood volume. The blood is, therefore thickened, which makes it more likely to clot. Dehydration can result from the very dry air in-cabin, alcohol consumption, coffee and inadequate intake of water and non-alcoholic drinks.

IMMOBILITY

The on-board safety procedures of ALL airlines and the need for the aisles to remain clear for the cabin crew enforce relative immobility of the passengers. Many passengers remain immobile for long periods of time.

Certain passengers will have certain predisposing risk factors, as highlighted earlier. Airlines cannot prevent this. DVT tends to develop during long periods of inactivity. DVT may develop during a long flight and has been, wrongly dubbed ‘economy class syndrome’ because economy class seating has less leg-room, restricting passengers to minimal movement. Studies have shown, however, that DVT occurs in Business & First class also.

Establishing the degree of risk to an individual is difficult. However, research has shown that Deep Vein Thrombosis / Pulmonary Embolism is definitely related to travel. Evidence suggests that there is an increased risk associated with flying when compared with other forms of travel, probable for thereasons above.

Conclusions

* DVT clearly related to long distance travel

* Air-travel poses additional risk factors

* Multiple complications can occur, including a lethal Pulmonary Embolism

* Many passengers will have inherent increased risk(s), which cannot be prevented.

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USA websites on DVT: www.preventdvt.org www.dvt.net/home.jsp

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