Economy class syndrome: rheology, fluid balance, and lower leg edema during a simulated 12-hour long distance flight.

In order to study pathological changes that might lead to deep vein thrombosis and pulmonary embolism in long-distance air travel passengers, 12 healthy volunteers were investigated during 4 simulated 12-h flights (day and night). The influence of repeated leg exercise was compared with constant sitting. Plasma viscosity, hematocrit, albumin, fluid balance, and lower leg swelling were measured. Rheological studies showed only circadian rhythm alterations. An average of 1150 ml fluid was retained, which correlated with an increase in body weight. The lower leg volume increase was significant, but not pathological. Periodic leg exercising showed no measurable preventive effects. These changes in healthy human volunteers are within physiological variations and are not sufficient to provide a definitive cause of venous thrombosis in healthy passengers. They do, however, suggest alterations produced by long-distance air travel that could intensify the risk of developing deep venous thrombosis in passengers with predisposing risk factors.