My medical school friend, a dour Yorkshireman, was deep. Really deep, man, in 1970s speak! Strong and silent, slow to comment, but when he spoke his wisdom knocked people out. He knew more than us, we thought, because he was deep. But don’t aspire to another “deep,” which has a lot in common with my old friend; silent and knocking people out come to mind. The “deep” I am referring to isn’t followed by “man,” but “venous thrombosis” or DVT to its enemies. Sit up and take notice, because DVT loves finding pilots to toy with and when DVT plays, it plays rough.
DVT literally means veins deep inside the body contain clotted blood, most commonly in the legs and pelvis. Nothing to do with being a philosopher!
Blood travels to sublime anatomic destinations via arteries, muscular tubes transmitting the heart’s pulsations. Once nutrients and oxygen aboard arterial blood have disembarked in feet and femurs, thymus and toes, bereft of thrust, the blood ambles back to the heart through veins, larger than arteries and under lower pressure. Rudolf Virchow, a nineteenth century German doctor, noted that if venous blood flow becomes sluggish, if the vein is damaged or the blood has a tendency to clot ( hypercoagulable in doctor speak) then DVT is possible. A clot, once formed, can go a number of ways. The first is nowhere—it dissolves. However, it might occlude the vein causing limb swelling or, of major concern, it can fracture, reach the heart and thence arteries supplying all or part of a lung. This pulmonary embolus (PE) can cause sudden death, acute breathlessness, a bloody cough, or chronic lung problems. OK, you get the picture—DVT is serious. But why is this relevant to pilots?
Anything causing sluggish flow or hypercoagulability is a risk factor for DVT. This is where we come in. Sitting immobile in the cockpit for hours with our legs flexed at the hips slows venous blood return. Add dehydration at altitude, which is worsened by a thermos of java, effectively “thickening” the blood, and it is a nasty combination.
Although pilots do not drink alcohol in flight, passengers might and this also impacts blood flow. The old “eight hours bottle to throttle” is not good enough—the dryness from getting soused the night before a flight can lead to a hammering situation in your legs as well as your head! Factors making DVT more likely include obesity, smoking, pregnancy, certain medications (e.g., oral contraceptives), prior pelvic surgery, artificial hips, cancers, and family history of clots or any personal clotting history. So is wearing the wrong clothes! Absence of sartorial elegance can do more that make you look silly on the tarmac; tight belts, pants, socks, or other items that compress the soft area behind the knee are a no-no. Flared trousers are also out, but just for fashion reasons.
What are the symptoms of DVT? Sometimes a free ride in a white van with a noisy siren, so ideally avoid the darn thing. DVT may present with painful swelling and redness of one leg or with the aforementioned respiratory problems. Diagnostic confirmation requires the doctor asking key questions, a careful examination, ultrasound examination of the legs, chest radiograph, and maybe some other, fancier tests.
Treatment involves medication to reduce clotting, such as Warfarin (which is also used to kill rats!). If you have suffered a PE, a filter may be placed inside the vena cava, the main vein returning blood to the heart. Rather like a fuel filter, it removes small pieces of clot that could otherwise cause big trouble if they made it to your engine. Gary Crump, AOPA’s director of medical certification, told me that the FAA feels this is a reportable condition requiring a special issuance, but it is not a mandatory disqualifying condition, so under FAR 61.53 the airman and doctor could determine that once stable, even with a filter, one could fly on the current medical and report at the next renewal, at which time a special issuance would be required.
You don’t need to be a philosopher to know that you don’t want to have DVT or PE, so what preventive steps can you take? First, speak to your doctor as my comments are necessarily generic. However, simple steps such as avoiding tight clothes and staying properly oxygenated (See “ Fly Well: Diving to Great Heights,” March 2010 AOPA Pilot) and well-hydrated in the air and exercising your legs are good precautions. Specifically, bend and straighten your legs, knees, feet, and toes, pressing down with your feet and repeat every 15 minutes. A small daily dose of aspirin, which can help prevent all sorts of health problems, may be appropriate; check with your doctor. Additionally, consider graduated compression stockings, available from the drug store without prescription. Look for those that provide 15 to 20 mm of mercury pressure gradient (“15 to 20mmHg” on the packaging). British humor is littered with evidence of a penchant for cross-dressing, but this is one behavior not to giggle at.
In Britain, a clot is also a synonym for being a dope—get the hang of being deep, but don’t be a clot and let deep venous thrombosis hang you.
Dr. Jonathan Sackier is a surgeon and instrument-rated private pilot. E-mail the author at firstname.lastname@example.org.