Maintaining Your Health on Mackinac
Long Flights Can Increase Your Chance of Having a Blood Clot
By Yvan Silva, M.D.

It is becoming more common - the reporting of sudden collapse, and in some cases unexpected sudden death, of individuals on long airline flights. With the development of larger modern aircraft, and the scheduling of longer and longer transcontinental flights, the risks are increasing.

The anatomy of the veins of the lower human extremities consists of two systems - a superficial system, where the veins course under the skin, often visible in the feet, and a deep system, where the veins lie in the musculature and return all the blood into the pelvis en route to the heart. The two systems communicate with each other through perforators, small veins that pierce through the muscles and bring the superficial blood into the deep system. The venous system is a slow flow system compared to the arterial system, where the blood flows rapidly in a pulsatile fashion.

Stagnation of blood in the venous system can lead to clots, and clots, when they dislodge from the walls of veins, will travel toward the lungs. Depending on the size of the clots, the lungs can decompensate very rapidly, leading to severe lack of oxygenation of blood, and death. This phenomenon, pulmonary embolism, is one well known condition that is rapidly fatal, within a few minutes, somewhat comparable in intensity to a massive heart attack, where the arterial system is shut off by severe interruption of blood flow.

The deep veins of the lower extremities contain valves, which allow one-way flow to the heart. Indeed, the legs are known to physiologists as a "peripheral" heart, in that the muscles are constantly milking blood toward the heart; even in the standing position, blood flows against gravity upward, enhanced by this mechanism of muscle tonicity.

As the world continues to "shrink" with rapid long distance travel, people drive long distances and fly long distances for extended periods of time in a sedentary state, most often in a sitting position. Venous flow from the lower extremities becomes impeded for these long periods, leading to stagnation of blood and increased risk for clot formation. Long car and train rides may well cause this condition, but flying is more likely to, perhaps because of low air pressure and oxygen levels.

Deep Venous Thrombosis (DVT) is a term that is becoming very common to people in the travel business. It's also termed the "economy class syndrome" - here are people sitting in small, tight seats, in cramped, close cabins, without the opportunity to walk around and stretch. Narrow aisles are blocked regularly with food and beverage service, and it's a wonder that DVT is not more commonly reported than it is. Indeed, it is thought that clotting does occur commonly, but the clots are liquefied by natural physiological defenses and do not lead to clinical problems. Incidentally, these problems are also seen in first class and business class travelers, but less frequently, perhaps owing to the availability of larger seats and more leg room. Sitting for many hours without moving around slows the blood return from the legs, leading to stickiness of blood components to form clots. Small clots may form and dissolve naturally without the passenger even becoming aware of their occurrence.

According to a recent report in a major aviation journal, 200 people around the world have suffered from DVT in the last decade. The reports of fatalities are dramatic, and occur without any medical background risk factors. One example, reported a few years ago, described an 18-yearold female, an active collegiate volleyball player, who flew from Pittsburgh, Pennsylvania, to Charleston, South Carolina. Three days later she developed a swollen leg that turned purple, with severe leg and chest pains. She was treated effectively for DVT with blood thinners, and no risk factors were found in her past medical history. Later, it was discovered that she had a rare, blood-clotting disorder.

This issue has been known for decades, but worldwide attention became drawn to it when, in 2000, a 28-year-old woman died at Heathrow Airport in London, shortly after arrival of the 20- hour long flight from Melbourne, Australia. Blood clots had formed in the legs or pelvis and migrated to the lung, causing sudden death.

The risk is greatest for people with known health conditions which promote clotting, such as cancer, cardiovascular disease, and blood-clotting disorders. There are other risk factors; people older than 60, those who have had recent surgery, those in poor health, weight loss, pregnant women, and those taking birth control pills or hormonal medication for post-menopause are also examples. The longer the flight, the greater the risk. The precise cause is not fully understood, and one study published in an international medical journal reported a 1% incidence among passengers with low to moderate risk factors, who had flown 10 hours or more during the past weeks. Airlines have developed the technology to offer more and more transcontinental nonstop flights. Just recently, Singapore Airlines introduced a debut 18.5-hour nonstop flight from Singapore to Los Angeles, California. Plans are underway to increase the sectors for long nonstop transcontintental flights.

For people older than 60, with moderate to high risk, and those who have had this problem before, experts recommend the use of compression stockings to enhance blood flow by putting circumferential pressure on the legs. For this purpose, the ones proven most effective are those individually made by prescription from a doctor, rather than the generic, over-the-counter models. For people at high risk, including those with cancer, heart disease, clotting disorders, or recent surgery, it is best to see a doctor, and if indicated, take medicines designed to prevent blood clots. It is important to remember that the condition can become manifest within a week or two after the flight, so that symptoms of intermittent leg pain that feels like a cramp, redness or swelling of a calf, chest pain, and shortness of breath require medical attention. Several patients who have had this condition have been reported to have flown on numerous occasions safely since, while continuing to take anticlotting medication.

The World Health Organization has organized a large study to examine this and other factors relating to DVT and air travel. Several medical groups have joined with the airline industry to enhance public education on prevention and recognition. A coalition to prevent DVT, formed by medical and public advocacy groups, has a Web site, www.preventdvt.org, with information useful for the traveler.

Travel agencies, sales catalogs, and airlines are making available several educational tools and information to help travelers exercise in flight.

Dr. Silva is a professor of surgery at Wayne State University and a resident of Woodbluff on Mackinac Island.