May 10, 2001 -- Attention summer travelers: Are you phobic about those cheap airline tickets you just bought? Well, stand by. The controversy about so-called "economy class syndrome" isn't over, so there's still no telling whether you need to upgrade them.
A new study finds that as many as 10% of airline passengers may be at risk -- more than any other study has shown. Yet other experts contend just the opposite, saying that very few are truly at risk.
Economy class syndrome is the term that's used to describe deep vein thrombosis, or DVT, a medical condition that occurs when people develop blood clots in the deep veins of their legs. It's most likely to happen when people sit for long periods of time -- like long flights in cramped economy-class airplane seats -- and blood does not move through vessels adequately. These blood clots can travel to the lungs or other areas, causing strokes, severe organ damage, or death.
But do the blood clots pose a serious threat to the general flying population? That's what researchers have been trying to determine.
In the first randomized controlled trial to assess risk of DVT on long-haul flights (about eight hours long), 10% of the study group developed "clinically significant abnormalities of the lower limb veins," writes lead author John H. Scurr, a researcher with the Royal Free and University College Medical School in London. His study appears in the current issue of The Lancet.
A total of 124 men and 124 women -- all over age 50 -- took part in Scurr's study. Each was given an ultrasound exam to ensure they had no history of deep-vein problems.
Elastic compression stockings -- the kind worn by many hospital patients after surgery -- were randomly given to half the group; the other half were given nothing. The people then took separate flights to different destinations, all traveling in economy class. Within 48 hours of returning to London, each came back to the hospital for another ultrasound to determine whether they had developed blood clots.
Researchers found that 12 of the passengers had developed blood clots, and all were in the group without stockings. None of the travelers who wore the stockings developed clots.
The data, says Scurr, point to the effectiveness of elastic stockings to reduce risk of blood clots after surgery. He writes, "our findings strongly suggest that stockings also protect against symptomless DVT after air travel."
Scurr further indicates that his numbers may be conservative because ultrasound detects from 79% to 99% of calf vein thrombosis. "Our data may have underestimated the true rate of calf vein thrombosis by as much as 30%," he writes. But others have their own opinion about the study.
"Potentially flawed study," says Jack Hirsh, MD, director of the Hamilton Civic Hospital Research Center at McMaster University in Ontario.
Hirsh has run some epidemiological numbers of his own: "In the general population, a 20-year-old has a 1/5,000 risk per year; an 85-year-old has a 1/100 risk because of age and other illnesses; middle-aged people fall somewhere in the middle, from 1/1,000 to 1/500 per year -- if they don't fly," Hirsh tells WebMD. "Flying may increase thrombosis by 1/25."
The bottom line is that there is a "very low risk, even if you are flying," says Hirsh.
Who is at risk of DVT? Those who have family history or multiple episodes of thrombosis, as well as patients with active cancer, Hirsh tells WebMD
So why did Scurr get such high numbers? "They were looking for silent clots, and what they found were very small [ones] that were of no risk to anyone," says Hirsh. "These teeny-weeny clots are absolutely meaningless. It's even possible that if we were to look in our legs after lying in bed for eight hours we would find them."
Hirsh's bottom-line message: "In the otherwise healthy individual, the risk of clotting is very low," he tells WebMD. "It's a very uncommon event."
If you are still concerned and want to hedge your bets, Hirsh offers suggestions: Practice isometric exercises -- muscle contractions -- for five minutes every half hour, or do them for one minute every 10 minutes. "Those numbers are just pulled out of the air," he says. "The point is, contracting your muscles frequently pushes blood up towards your heart."
Also, make sure you don't get dehydrated. Drink water, not coffee or alcohol, both of which can stimulate urination. "What pilots do is drink a large glass of water per hour," Hirsh tells WebMD. "More and more airlines are providing people with bottled water. And they will replace it.
"We advise only people with previous venous thrombosis and swelling of the legs to wear [elastic stockings]. Otherwise, we really don't advise it. They're quite hot to wear, difficult to put on and take off, and they are quite expensive."