The dangers of air travel

The general volume of air traffic has risen greatly in recent years and an important component of this is the increase in the number of long-haul flights. According to International Civil Aviation the annual number of flight passengers exceeded 1647 million in 2006 and that number is expected to rise by 4.4 per cent each year by 2015 (World Health Organization, 2007). Contemporary aircraft can cover longer distances without the need for stop-over, thus prolonging the duration of the flight. Moreover, in order to fit more passengers on the economy class flights, the airline industry tends to put additional seats in the cabin. This reduces the already insufficient legroom space even further, consequently increasing passengers’ immobility.

The altered and restricted environment in an air-craft cabin, carries possible health risks for people aboard. One such flight-related danger is the development of a deep vein thrombosis (DVT) in the lower legs, which can lead to potentially fatal conditions, particularly pulmonary embolism (PE). DVT relates to a condition caused by the formation of a blood clot (i.e. thrombus) in deep veins usually of the legs. When such blood clot breaks off it can travel through the veins back to the heart, and eventually be pumped by the heart into the lungs causing a blockage leading to the potentially fatal condition called pulmonary embolism.

Venous thromboembolism (VTE – both DVTs and PEs) after long-haul flight was first reported more than 50 years ago (1954). Since then multiple case reports and epidemiological studies provided further evidence of an association. VTE have been connected with at least 577 deaths on 42 of 120 airlines from 1977 to 1984 (25 deaths/million departures), although a proportion of such cases go unreported (Greenleaf, et al. 2004) primarily due to the fact that majority of DVT are asymptomatic and resolve spontaneously or occur days after the flight. It is crucial to acknowledge the fact that VTE is not unique to air travel but it is a complication also associated with other modes of transport, or rather any form of prolonged immobility.

It remains unclear whether the aircraft-specific factors, such as hypobaric hypoxic conditions and lower humidity, create an increased risk compared with seated immobility at ground level. There is very little evidence for the direct causative relationship between air travel and DVT in the healthy flying population. In fact the major danger is for those people who fly with multiple risk factors for DVT. For example, mutation in certain genes responsible for increased blood coagulability, history of VTE, venous insufficiency, obesity, and infectious diseases, to name a few.

Nevertheless, various preventive treatments and techniques have been proposed as countermeasures for possible flight-induced DVT. One such procedure is exercise of the lower extremities, especially the calf (soleus and gastrocnemius) muscles, in order to increase intracapillary pressure facilitating venous flow thus preventing blood from clotting (Paganin, 2003).

What is less clear is the appropriate frequency, duration and intensity of exercise in different environments and different populations. Identification of this will help to minimise risks during travel. Here at LSBU we are currently carrying out experiments that are attempting to answer these questions.