Low cabin pressure isn't to blame for the rare but dangerous blood clots that some passengers get during long flights, new evidence suggests. The likely explanation for the phenomenon, sometimes called economy-class syndrome, is that long periods of sitting promote clots, particularly in susceptible people, investigators say.
Deep-vein thrombosis—a condition in which blood clots form in veins deep in the legs—can be lethal if a clot breaks away and travels to the lungs. Past studies suggested that the low air pressure on flights increases the tendency of blood to coagulate.
To test that possibility, William D. Toff of the University of Leicester in England and his colleagues simulated the atmospheric conditions of a daytime, long-haul flight. A few at a time, 73 healthy volunteers sat in an airtight chamber for 8 hours, as if they were in a cramped plane cabin.
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