Long-haul flights can be risky for people with certain types of heart and lung conditions, as well as anyone who has had surgery recently, investigators warn.

“The environmental and physiologic changes that occur during routine commercial air travel can incite or exacerbate preexisting cardiac and lung conditions,” Dr. Mark Gendreau of the Lahey Clinic Medical Center in Burlington, Massachusetts, one of the study’s authors, told Reuters Health.

“People should check in with their physicians if they do have significant health problems before they get on a plane,” he advised.

Nearly 2 billion people fly every year, Gendreau and Dr. Danielle Silverman of Georgetown University Hospital in Washington, DC, note in a report in the Lancet medical journal.

The drop in pressure that occurs as an airplane reaches cruising altitude makes it tougher for the blood to hold oxygen, Gendreau noted. Most healthy people can cope with this reduction in oxygen saturation, but for people with illnesses that cause them to have low oxygen blood levels in the first place, such as emphysema or congestive heart failure, it can be hazardous, particularly on flights more than a couple of hours long. Doctors may advise these patients to bring oxygen with them on the plane.

Flying too soon after surgery can also cause problems, Gendreau added. This is a particular concern for people who travel to have certain procedures, for example someone who goes to Canada to have laser surgery for vision correction or heads to Latin America for inexpensive plastic surgery. “Whenever you have elective surgery or any elective procedure, you should always ask your surgeon when it would be safe to travel,” he advised.

So-called long-haul flights, defined as any trip lasting eight hours or more, are known to increase the risk of a potentially fatal blood clot forming in the legs, Gendreau added. The risk of these blood clots is quadrupled during long flights for the average person, while people with conditions that promote blood clotting are at even greater risk.

The best strategies for preventing these deadly blood clots are common-sense, Gendreau said, and include keeping well-hydrated, avoiding caffeine and alcohol, getting up to stretch and walk around the cabin, and doing calf-stretching exercises in your seat. “For most people that’s sufficient to minimize your risk,” he added.

One in-flight health concern that people shouldn’t worry about too much is the risk of contracting contagious disease, the investigators say. While flights can indeed promote the geographic spread of disease during an epidemic, according to Gendreau, the risk of catching the infection is typically limited to people sitting within two rows of the contagious person. In fact, he pointed out, because airplanes use HEPA filters to keep cabin air clean, a plane may actually be a bit safer than other modes of mass transportation, for example buses and subways, at least when it comes to catching the flu.

SOURCE: The Lancet, online February 19, 2009.