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To the Editor: In their single-blind crossover study, performed in a hypobaric chamber, Dr Toff and colleagues¹ did not find relevant prothrombotic alterations in healthy individuals after 8 hours of sitting under simulated hypobaric hypoxic conditions. Data were similar after sitting under normobaric normoxia. The authors rejected the hypothesis that hypobaric hypoxia of the degree that might be encountered during long-haul air travel is associated with prothrombotic changes in the hemostatic system in persons at low risk for venous thromboembolism.

We believe that additional factors must be considered. This study was done under simulated conditions, not the real conditions of a long-haul flight. A major difference may be traveling as a psychophysical stressor. Mental stress may influence coagulation and fibrinolysis.² A study under real conditions of a long-haul flight showed a moderate coagulation activation.³ After 8 hours of flight, there were significant increases in activity of coagulation factors VII and . . . [Full Text of this Article]

Wolfgang Schobersberger, MD
wolfgang.schobersberger@umit.at

Beatrix Schobersberger, MD
Institute for Leisure, Travel, and Alpine Medicine
University for Health Sciences, Medical Informatics and Technology
Hall, Tirol, Austria

Markus Mittermayr, MD; Dietmar Fries, MD
Clinic for General and Surgical Intensive Care Medicine

Werner Streif, MD
Department of Pediatrics
Medical University of Innsbruck
Innsbruck, Austria