2014-05-31 / Columnists

Maintaining Your Health on Mackinac

Air Travel and Blood Clots May Be Linked to Sudden Collapse
By Yvan Silva, M.D.

A phenomenon that is becoming better known is reported incidents of sudden collapse, in some cases, unexpected sudden death of individuals on long airline flights. With the development of larger modern aircraft and the availability and scheduling of longer and longer transcontinental flights, the risks are increasing. Long distance travel by land vehicles also poses such risks when travelers are confined and seated for long periods of time.

The anatomy of the veins of the lower extremities in humans 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, when they dislodge from the walls of veins and travel toward the lungs. Depending on the size of the clots, the lungs can be affected very rapidly, leading to severe lack of oxygenation of blood and, possibly, 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 critical interruption of blood flow to the heart muscle.

The deep veins of the lower extremities contain valves, which allow a 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 towards the heart; even in the standing position, blood flows against gravity upwards, 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 long periods of times in a sedentary state, most often in a sitting or reclining 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 common to people in the travel business. It is also termed the economy class syndrome, where passengers sit in small, tight seats in cramped, close cabins without the available opportunity to walk around and stretch. Narrow aisles are blocked regularly with food and beverage service. 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 don’t lead to clinical problems. Incidentally, these problems are also seen in first class and business class travelers, but less frequently, perhaps because of the availability of larger seats and more leg room. Sitting for many hours without moving around slows down 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 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 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 female 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 postmenopause are also examples. The longer the flight, the greater the risk. The precise causation 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. For example, Singapore Airlines introduced an 18.5-hour nonstop flight from Singapore to Los Angeles a few years ago. Recently, there have been additions by a few airlines of direct, nonstop flights between intercontinental sectors taking more than 14 to 16 hours.

For those 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 anti-clotting 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 that is 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.

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