60,000 Miles or So, There and Back (Part Two of the Journey)

In the last post, we discussed the mechanics of the network of blood vessels that supply the entire body with the essential-to-life nutrients that keep organs functioning optimally.

Pilots need to be especially careful with this delicate balance of thrust and drag of blood within the conduits that are the supply chain for life-sustaining cargo. One concern for pilots and passengers alike in both GA and commercial airline travel is the risk of blood clots.

There are numerous factors that can cause a blood clot inside a vessel and all are common in the cockpit environment. Dehydration is common at high altitudes and is due to low humidity and dry air that cause the body to lose free fluid through the lungs and skin. This in turn increases the drag side of that balance we talked about last time, the thickness (viscosity) of the blood. The more viscous the blood, the more sluggish the blood flow and the more likely it is to have intravascular clot formation. Clot formation in the veins results in a DVT (deep venous thrombosis) and if it forms in the legs, where it is most common, the clot can break off and travel to the lungs, where it will cause a potentially fatal pulmonary embolism. Clot formation that occurs in an artery results in loss of downstream circulation and death of all the tissues that are supplied. A thrombosis (clot) in the coronary vessels results in a heart attack, in the brain the result is a stroke, and in the abdominal vessels the result is an intestinal infarction. All of which are likely to be fatal.

The first takeaway lesson from all this is that while in the air, drink lots of fluid (preferably water) and stay hydrated. Although it might be a little uncomfortable and inconvenient, the best guide to the amount of fluid to take in on a flight is having to urinate. The reason behind this is that the kidneys have about the highest blood flow requirement of any part of the body in order to work properly, so if you drink enough to have to use your relief tube, you are providing the kidneys with enough blood flow to do their job. If the kidneys get enough blood flow then every other organ in the body is happy and healthy as well.

Another predisposition to blood stasis and clot formation is sitting in one position for a long time, which can cause venous clotting and another whole problem. This is especially true in the average GA front seat, where there is not a lot of room to be active and move around. So, the second thing to remember is that it is important to stretch as much as possible and to keep flexing and stretching every half hour or so while on long flights.

If a person is particularly prone to clot formation for any number of reasons, a physician may place them on a “blood thinner,” an anti-clotting medication such as aspirin, a stronger drug called Coumadin, or one of the newer blood-thinning agents. Physicians recommend (although there are recent revisions that narrow the broader indications) that adults take a baby aspirin every day. Aspirin interacts with elements in the bloodstream to make them less “sticky” and is usually a benign medication. Certainly consult a physician first as there are individual contraindications such as ulcer disease, but in general there are good reasons for pilots who spend a lot of time sitting at high altitudes to take a baby aspirin every day.

So, putting it all together with the stickiness of blood and blood flow side of the equation, there are a number of other important reasons to control the resistance and pressure sides of blood flow. All those 60,000 miles of blood vessels are lined with a very delicate interior cell coating called the “endothelium.” This crucial “slippery” cellular lining is designed to prevent activating those factors that lead to intravascular blood clotting and promote smooth transit of blood through the body. Elevated blood pressure and excessive shear forces in arteries lead to little micro tears in this delicate lining of the blood vessels. These micro injuries cause deposits of the elements (specifically platelets) of the blood-clotting cascade. These little particles start to accumulate and build up around raw surfaces and micro tears that are no longer smooth and clear. This ultimately leads to formation of fatty (cholesterol) “plaque” material that impedes blood flow. Just think of this like contamination and debris in the fuel tanks that plug up the aircraft fuel lines and prevent free flow through the lines to the engine. To protect all these miles of fragile fuel lines from this debris, physicians will also prescribe medications to lower the amount of fatty elements in the blood with medications known as “statins.”

In addition to hypertension, there are all kinds of bad habits that can promote increased fatty content of the blood and injury to the vessels such as smoking and excessive alcohol intake. As atherosclerosis advances, the blood vessels become stiffer, less compliant, and are prone to blockage and occlusion. Just like a partially blocked fuel line can build up pressure and burst, stiff arteries can dilate (that is called an aneurysm) and rupture, causing sudden death from internal bleeding. This is a more gradual process than intravascular clot but both still have the same endpoint, which is stroke and heart attack and risk of death.

Maintaining good cardiovascular health requires attention to all these details. Keep those thousands of miles of fuel lines open to maintain delivery of oxygen and nutrients to all those far-flung places within your body so that each in turn can keep you active, vigorous, and happily flying toward that 60,000-mile goal. In the next post we will talk about all those important fuels that these thousands of miles of pipes deliver.

Kenneth Stahl, MD, FACS

Kenneth Stahl, MD, FACS is an expert in principles of aviation safety and has adapted those lessons to healthcare and industry for maximizing patient safety and minimizing human error. He also writes and teaches pilot and patient safety principles and error avoidance. He is triple board-certified in cardiac surgery, trauma surgery/surgical critical care and general surgery. Dr. Stahl holds an active ATP certification and a 25-year member of the AOPA with thousands of hours as pilot in command in multiple airframes. He serves on the AOPA Board of Aviation Medical Advisors and is a published author with numerous peer reviewed journal and medical textbook contributions. Dr. Stahl practices surgery and is active in writing and industry consulting. He can be reached at [email protected].

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