TUESDAY, May 16, 2006 (HealthDay News) -- The reduced air pressure and oxygen levels that come with air travel don't contribute to potentially deadly blood clots in the legs or lungs, a British study found.
But the chance of danger does exist for passengers on long-distant flights, especially older people and those with certain risk factors, such as a family history of a condition called deep vein thrombosis (DVT), according to experts, including the cardiologist who led the study.
"It is quite clear that there is a link between travel and thrombosis [blood clots]," said Dr. William D. Toff, a senior lecturer in cardiology at the University of Leicester and lead author of the study in the May 17 issue of the Journal of the American Medical Association. "What is not so clear is if there is anything that distinguishes the airplane cabin that makes air travel quantitatively different."
To answer that question, Toff and his colleagues had 73 healthy volunteers sit in a hypobaric chamber with slightly reduced levels of oxygen and air pressure, simulating an eight-hour airline flight. The volunteers were allowed to walk around for five minutes every hour, but otherwise remained stationary.
Blood tests done before and after the eight-hour session showed no change in signs indicating clot formation, the researchers found.
"We looked specifically to see whether low pressure and low oxygen activate the clotting mechanism," Toff said. "We found no evidence that they did."
But, he added, the experiment didn't rule out a potential effect for some individuals. All the participants had no risk factors for blood clots. "We can't rule out that people with multiple risk factors might respond differently to hypoxia [low oxygen]," Toff said.
A key point of the experiment is that "it doesn't diminish the fact that there is a link between long-distance travel and thrombosis," he said. "Travelers should take sensible precautions."
DVT is sometimes called "economy class syndrome" because the risk is higher for people who sit in cramped quarters for long periods. By ruling out the potential effect of cabin environment, "the study can refocus attention on the mechanics of blood flowing in the veins," said Dr. Christopher Cannon, an associate physician in the cardiovascular division of Brigham and Women's Hospital in Boston. "Getting up and moving around is the best way to avoid blood clots from developing."
Clots that form in leg veins can cause severe damage or death if they travel to the arteries of the brain or the lungs. The risk is so well known that "many airlines have exercises that can be done while seated," Cannon said. "Stretching and moving your muscles can improve blood flow in the veins."
Dr. Franklin Michota, head of the section of hospital medicine at the Cleveland Clinic, said the study may have underestimated the overall risk because it did not include many older people, who face a greater chance of DVT. Only 12 of the participants were over 50.
"This is not a particularly old group of people they studied, and they all were skinny," Michota said. "They found no significant differences in healthy individuals. The real question is whether there is a significant difference in unhealthy individuals."
The list of potentially vulnerable people can include healthy individuals, Toff said, such as women who are pregnant or are taking oral contraceptives.
To help reduce your risk of DVT, Toff also suggested wearing compression stockings. And people at very high risk might even consider getting an injection of the blood thinner heparin before a long flight, he said.
More information
To learn more about deep vein thrombosis, visit the NASA Occupational Health.
