Any person who sits still for a long time may develop small clumps of clotted blood in the lower legs. It can occur following a long car, bus, train and plane journey. First Report It was recognised by a physician who travelled from Boston to Venezuela in 1946 on a non-stop flight lasting 14 hours. Signs occur days or weeks postflight. Compression of the thighs by seat edge.
Lower pressure increases coaguability factors in the blood.
It can also occur in business class where the legrest puts pressure on the calves. People over forty years of age. Individuals over six feet or under five feet tall. People with varicose veins. People with heart disease.