How cramped are our skies?

By Andrew Demaria
CNN.com Writer

Emma Christofferson was sitting on a Qantas plane on her way home to England after a three week holiday in Australia in October last year. The 10,000-mile journey to London's Heathrow airport takes at least 20 hours and usually involves at least one stopover.

Towards the end of the flight Christofferson began to feel unwell. The 28-year-old Briton had been sitting in her economy class seat for a long time and may have dismissed her suffering as one of the irks associated with travel.

After disembarking at Heathrow, Christofferson made her way to the arrival hall with the other passengers. Suddenly, unable to breathe, she collapsed.

Christofferson was dead before she reached hospital.

A post mortem examination confirmed the cause of death resulted from a deep vein thrombosis (DVT). While Christofferson was sitting in her seat, a blood clot developed in her leg, eventually making its way to her lungs. The result was what doctors call a pulmonary embolism -- the blocking of a major artery to the lung. The effects were fatal.

Christofferson became one of the youngest victims of DVT and her death made headline news across the world.

In recent months the condition has become known as 'economy class syndrome' with many arguing that the cramped seating arrangements on airlines increases the risks of developing a thrombosis.

The term, in use since 1977, is slightly misleading. A number of DVT cases related to passengers who had recently traveled by air had been sitting in business or even first class.

Airlines, backed by medical research, argue that a DVT can be set off by many factors other than air travel.

That hasn't stopped a flood of publicity about DVT-related incidents from airline passengers and medical experts, nor has it reduced the threat of legal action.

There is no conclusive medical evidence of a direct link between air travel and DVT, but the exposure has raised concerns among members of the public who rely on air travel.

A recent disclosure to CNN.com by a doctor in Japan reveals that his department admitted 12 patients with serious DVT-related conditions directly from Tokyo's international airport over a period of 20 months. Two patients, both women in their sixties, were pronounced dead before they reached the hospital.

This follows a report in an Australian newspaper quoting coroners report that 18 airline passengers in Australia have died since 1992 of the so-called 'economy class syndrome'.

In other major events since Emma Christofferson's death in October 2000: