Chronic diseases and health promotion

WRIGHT Centres

WHO Research Into Global Hazards of Travel

Group I: Epidemiological studies

Participating centre - Leiden University Medical Center, Leiden, and Academic Medical Center, Amsterdam, the Netherlands

Venous thrombosis occurs in 1-3 per 1000 people per year. Air travel has been associated with venous thrombosis in many case reports, but the few controlled studies are contradictory. Elucidation of the magnitude of the risk has direct public health relevance in helping to decide which prophylactic measures may have a net beneficial effect, and which might be ill-advised. Since hundreds of millions of people travel by air each year, even a risk increase that is small in absolute terms may have major public health impact. These studies focus on clinical endpoints to estimate the magnitude of the risk and contributing risk factors. The results will be useful for studying the effect of interventions.

Group II: Pathophysiological and coagulation studies

Participating centre - Leiden University Medical Center, Leiden, and Academic Medical Center, Amsterdam, the Netherlands

Airliners provide a safe and effective means of rapid transportation. Each year more passengers travel over increasing distances. Physicians working close to major airports have observed patients presenting with thromboembolic problems following air travel and published these as case reports. The purpose of this study is to establish the overall incidence of deep vein thrombosis in long haul airline passengers and to assess the factors associated with the risk of thrombosis. The studies in this group aim to establish the incidence of deep vein thrombosis following airline travel in passengers employing a series of measures of DVT prevention. The rates of symptomatic and asymptomatic DVTs will be investigated including an assessment of the proportion of distal and proximal deep vein thrombosis.

Group III: Pathophysiological study on hypobaric hypoxia

Participating centres - Leiden University Medical Center, Leiden, and Academic Medical Center, Amsterdam, the Netherlands, the University of Leicester, Leicester, United Kingdom

It is generally accepted that prolonged immobility predisposes to venous thromboembolism (VTE) and that this may be an important factor in the causation of travellers’ thrombosis. It is not clear, however, whether the risk associated with long-haul air travel is qualitatively different from any other form of transport or from prolonged sitting in other circumstances. The aim of the study is to determine whether exposure to hypobaric hypoxia, at levels comparable to those that might be encountered during commercial air travel, promotes a hypercoagulable state that could predispose to VTE. The effect of prolonged sitting in the coach position under normal atmospheric conditions will be evaluated as a control condition and this may provide useful insights into the risk associated with immobility alone.

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