James Doty had flown across the Pacific Ocean at least a dozen times when he crossed it again to deliver a series of medical lectures in Taiwan. On the 14-hour flight back to America, he relaxed and fell asleep for almost the entire flight, as usual.

"When the plane landed in Los Angeles, I grabbed the carry-on luggage and found I was profoundly short of breath... It was like when you take a fish out of water. You can't breathe," says the doctor, who was in his mid-forties at the time and on the clinical staff at Stanford University Medical School. He felt a pain in his leg, then noticed a knot in his calf about four inches long.

But Doty ignored both the pain and his shortness of breath and went straight from the airport to a meeting. He became increasingly worried, however, as his heart continued to race and he found himself gasping for air whenever he spoke. When he finally went to an emergency room, doctors told Doty he was suffering from deep vein thrombosis (DVT), a condition that involves a blood clot in a leg. In Doty's case, the blood clot broke off and traveled through the bloodstream to his lungs.

After a week in the hospital, he recovered fully with no complications. But a year later, a 45-year-old woman from Uganda wasn't so fortunate. After landing in Montreal following a flight from Entebbe in August 2000, Mariam Kyambadde died from blood clots to her lungs that started in her legs as deep vein thrombosis.

Doty could have died too, with the likelihood even greater if the clot had lodged in his brain or his heart.

Like Doty, countless passengers have been afflicted with DVT while flying long distances. In fact, two studies released in the Archives of Internal Medicine suggest that long-distance flights put people at increased risk of getting a potentially fatal blood clot.

One study looked at 964 patients who had traveled more than eight hours and found that a long trip more than doubled their risk of getting a blood clot in their legs.

In a separate study of 420 patients, researchers found that air travelers with a certain genetic makeup that prevents clots from breaking up in their bodies were up to 16 times more likely to get a clot, and women taking oral contraceptives were 13 times more at risk of suffering from a clot.

Many of the travelers who got clots were people older than 50 and were overweight or obese. In many cases, passengers reported sitting immobile for the entire flight.

Deep vein thrombosis is also called traveler's thrombosis because doctors believe that sitting immobile for hours in a cramped space, which is often the case with travelers, can lead to the condition.

"It's the stationary sitting position that is dangerous in many ways," says Barbara Alving, MD, a hematologist and former deputy director of the National Heart, Lung, and Blood Institute. "Not moving around while in a sitting position is bad overall. It leads to clots and cramps."

Indeed, any unusually long periods of inactivity -- whether you're in a plane, train, automobile, or even your office chair -- can impede blood circulation. In turn, the pooled blood can cause a thrombus (clot) that can break off and travel to your heart, lungs, or brain. (The traveling clot is known as an embolus.) If the clot reaches your brain, it may cause a stroke; if it gets to your heart, it could lead to a heart attack. You might feel short of breath if the clot reaches your lungs, as it did in Doty's case. The media have dubbed this condition "economy-class syndrome," because the crowded conditions on many forms of transportation prevent people from stretching and moving around.

Passengers may not feel the symptoms right away, and it's possible for a clot to dissolve without causing any problems. Nevertheless, experts say all travelers need to be aware of the potential dangers. "I recently treated a gentleman who developed a clot after a 20-hour car ride," Alving said.

In addition, being relatively young, fit, and healthy doesn't necessarily protect you from DVT. In 2000, three coaches and trainers of a British Olympic team developed travelers' thrombosis during a stopover in Singapore on a flight bound for Australia. All three were between 34 and 45 years old. After developing pain and swelling in their calves, they had to be treated immediately.

Researchers aren't sure why athletes seem to be vulnerable to developing blood clots on flights, researchers theorize it could be because they're more likely to have bruised or torn muscles that are prone to clotting. Another theory is that athletes generally have a lower heart rate when they are resting, and consequently slower blood flow. But athletes aren't the only ones at risk.

In another case, 28-year-old British resident Emma Christofferson died after collapsing at London's Heathrow Airport following a 12,000-mile flight from Sydney, Australia. Soon afterward, British Airways began warning passengers about DVT. Other airlines with transoceanic flights began to show videos warning passengers about the dangers of remaining motionless during the flight.

Kathy Peach, a spokeswoman for Northwest Airlines, says the US-based airline developed an instructional video to show passengers exercises to do during long international flights. The airline also offers passengers information on its Web site about the risk of getting blood clots, particularly on long flights.

"Because people tend to sleep on international flights, they need to be reminded that healthy travel includes periodic movement," Peach said.

Not surprisingly, international travelers may be at the highest risk. In one well-publicized study, researchers looked at all 56 cases of pulmonary embolisms experienced by passengers at Charles de Gaulle Airport in France between November 1993 and December 2000. According to their report, published in the September 2001 New England Journal of Medicine, the researchers found that the risk of suffering from the syndrome increased on long-distance flights. Interviews with the passengers were also revealing: Forty-two of the 56 passengers studied said they never left their seats during the flight. Most of those who suffered embolisms were in economy class.

But is there a link between DVT and economy class? Critics of the airline industry contend that cramming passengers into smaller seating areas contributes to the incidence of travelers' thrombosis. Not only do passengers have less room to move about, they say, but it's more difficult to squeeze past people on the way to the aisle.

Critics point to airline deregulation in 1978, which over the 1980s and '90s, led many companies to reduce the space between rows in economy-class cabins. On international flights, for example, the space between a fixed point on one seat and the same point on the seat in front of it used to be 35 to 36 inches. On most flights today, that space is a mere 31 to 32 inches.

To attract more passengers, American Airlines launched a $70 million program in 2000 to increase the space between seats to 33 to 35 inches, eliminating an average of two rows per plane in all 850 domestic and international aircraft. "The number one complaint of passengers was the cramped seating conditions and the lack of room," said Al Becker, a spokesman for American. "Making our customers happy and comfortable was our main motivation. However, we knew in an indirect way we would help passengers avoid the health risks associated with cramped seating conditions."

Peach of Northwest Airlines, however, insists the incidence of DVT isn't related to overly crowded flying conditions. "It can happen sitting at a desk too long or in a car, train, or bus while being immobile," she says.

In fact, DVT may be behind some wartime "mystery deaths." During the air raids of World War II, people often fled to crowded bomb shelters and slept on deck chairs. Some died mysteriously in their sleep. Dr. Peter Charlesworth, a vascular surgeon who has studied dozens of such deaths that occurred in London during the 1940s, says he suspects undiagnosed blood clots were the cause.

Some researchers agree that the term "economy-class syndrome" is inaccurate, since at least a few people stricken with DVT had plenty of room to move around. In 1994, for example, former Vice President Dan Quayle suffered a blood clot in his lungs after flying in a first-class cabin.

But researchers also note that the pressure inside the cabin of an airplane creates a special condition not found in other forms of travel. Even in commercial jet cabins, the pressure is comparable to elevations of 5,000 to 8,000 feet above sea level, preventing blood from flowing as freely as it would if passengers were in a car or on a train traveling at lower elevations.

Those most susceptible to travelers' thrombosis are senior citizens whose circulatory systems don't work as well as young people's. "The veins have pumps and valves and they lose their function, thus blood pools more easily," Alving says. Anyone who has previously experienced thrombosis, or has a family history of DVT should be especially cautious on long flights. Researchers say other high-risk groups include people who are overweight, cancer patients, pregnant women, people who have had recent surgery, and those taking oral contraceptives or hormone replacement therapy.

But like Doty, who had no health problems, many passengers are vulnerable to developing DVT without being in one of the high-risk groups. For Doty, the danger was compounded by the alcohol he drank the night before flying, which helped dehydrate him. And he slept when he might have been drinking fluids to counteract the dehydration. Now Doty never drinks alcohol on international flights. But he does drink plenty of water, and he makes a point to move around whenever possible.

Experts interviewed advise passengers to take precautions on long-haul flights or any other form of travel where movement will be restricted for four hours or more. Here are some suggestions to decrease your risk:

After his own experience, Doty believes airlines should warn passengers that DVT is a potentially life-threatening condition, and should make sure all travelers get concrete suggestions on how to avoid it. "I really think it should be just like (airbags) in cars," Doty says. "It's a serious problem."

-- Tim Fitzgerald is an associate editor at Consumer Health Interactive.

References

First published March 13, 2002
Last updated February 26, 2008
Copyright © 2002 Consumer Health Interactive