Blog # 150
Andrew Siegel, M.D
It is Easter and Passover week and a very busy time for travel, so I thought this subject would be appropriate. It is fitting that as I am writing this, I am on a Delta jet en route to Sarasota.
Have you visited the mountainous regions of the Western USA, perhaps to go skiing? Let’s take as an example Park City, Utah, which has an elevation of about 7000 feet above sea level. For many who reside at sea level, visiting Park City can cause a number of symptoms on the basis of the decreased atmospheric (barometric) pressure and the diminished availability of oxygen. Until the body adjusts and adapts, many will experience a headache and perhaps some shortness of breath during routine activities such as walking up a flight of stairs, or perhaps have insomnia and shortness of breath in the wee hours of the morning.
What does this have to do with health issues related to flying? Simply that the cabin of a commercial aircraft is pressurized at 6000-8000 feet, very similar to the atmospheric pressure in Park City, and consequently there can be numerous health ramifications. Every year, billions of people travel by means of airlines. Because of a growing population, an ever-increasing aging population and an increase in air travel, there are more older and sicker people flying than ever before. For many, flying can be an unpleasant experience because of pre-flight stresses including airport turmoil, long TSA lines, the need to walk long distances, flight delays and the unpleasant processes of boarding and competing for carry-on luggage space; Inflight stresses including anxiety and fear of flying, loud noises, crying infants and children, your seat mate, vibration, turbulence, cramped seating (particularly non-aisle seating which reduces the opportunity to stretch and walk about the cabin), low humidity and decreased barometric and oxygen pressure; and post-flight stresses including the glacially slow process of deplaning, long walks, playing luggage roulette on the carousels, arranging transportation and jet lag.
Healthy people can usually easily handle the stresses associated with flying, but people with heart, lung and other health issues can become medically compromised when these stresses are imposed on the body. The good news is that planes are equipped with medical kits and defibrillators (AEDs) and flight attendants are trained in administering basic cardiopulmonary resuscitation (CPR) and in using the AED to treat passengers who have a cardiac arrest. In the event of a medical emergency, ground medical support teams can be contacted by the flight crew and medical consultation obtained. Rarely, a seriously ill passenger may necessitate flight diversion to an alternate airport for an emergency, unscheduled landing.
The key difference between the aircraft being on the ground as opposed to in flight is the atmospheric pressure. To reiterate, aircraft are not pressurized at sea level, but at 6000-8000 feet, and consequently the oxygen concentration in the air is diminished and there is a corresponding decrease in the oxygen carried in the blood (causing a state of hypoxemia). The decreased oxygen pressure decreases the saturation of hemoglobin (the protein that is responsible for transporting oxygen to our cells) to 90% vs. 97% at sea level. The healthy body can adapt and compensate by increasing the heart rate and respiratory rate, but those with cardiovascular and pulmonary compromise (angina, heart failure, recent heart attack, asthma, emphysema, etc.) may be unable to do so because of the decreased oxygen pressure and the very dry air conditions.
As a result of the decreased atmospheric pressure, not only is there is less oxygen available, but gases present in the cavities of our bodies expand in accordance with the laws of physics. Gases in our abdomen, middle ear and sinuses expand under the circumstance of low atmospheric pressure and may cause abdominal bloating, a crackling sensation within the ear and full sinuses, respectively.
Before takeoff, cabin pressure equals middle ear pressure, but during ascent to cruising altitude, middle ear pressure remains at ground pressure whereas the ambient pressure is now much less, so to equilibrate the pressures, air must be able to flow freely from the middle ear and from the sinuses to the outside. On descent, the opposite must be able to occur in order to equalize pressures. If pressure equalization cannot occur because of blockage of passageways due to a cold or allergy, consequences may occur including pain, bleeding and eardrum rupture. Problems of this nature are more severe during descent than ascent. It is helpful to do the following to help this situation: hold your nose shut with your fingers while exhaling forcefully against a closed mouth; swallow repeatedly; and chew gum.
Because of gas expansion, it is prudent to avoid gas-producing foods immediately before a flight. Since the lower air pressure of a plane allows intestinal gas to expand, the gases that normally exist in the gastro-intestinal tract will have more presence in flight. It is for this reason that flying too soon after gastro-intestinal surgery should be avoided as it can cause pain and bleeding.
Low cabin humidity (5-15%) is a certainty because air is obtained from the outside, where at high altitudes it is completely lacking in humidity. Consequently, the skin can get very dry as can any mucosal surface (moist area of the body) including the eyes, nasal passages, mouth, etc. Hydrating skin lotion, lip balm, artificial tears (especially for those who use contact lenses) and saline nasal spray and staying well hydrated by drinking plenty of water can be helpful means of combatting dryness.
Aircraft cabins are confined spaces in which a dense population is housed for hours in close proximity and thus the potential for transmission of infectious disease from passenger to passenger via breathing, coughing, sneezing, etc. Cabin air is a mixture of recirculated air and fresh air from outside; recirculated air is filtered to remove micro-organisms. Commercial airplanes use radial flow in which inflow (ceiling) and outflow (floor) ducts are separated, avoiding the mixing of cabin air. Any person with a contagious disease should postpone air travel to prevent the potential for transmission to others. Ozone, a respiratory irritant present at high altitudes, can find its way into the ventilation system when it enters with outside air. Most aircraft have ozone converters, which break down the ozone before it reaches the cabin
Venous thromboembolism (VTE) is a condition in which blood clots can develop within the veins of the legs under the circumstance of prolonged immobility, as can easily happen on a plane because of cramped seating and poor access to the aisle, often blocked with carts and other passengers. VTE usually causes pain and swelling in the involved leg and can become a very serious medical matter if pieces of the clot break off and propagate to the lungs, a condition known as a pulmonary embolism (PE), which can cause chest pain, shortness of breath, and can be potentially lethal as up to one quarter of PE are fatal. Certain situations create higher risk for VTE, including pregnancy, cancer, prior VTE history, and blood diseases that predispose towards clotting. In order to minimize risk for VTE, the following are recommended: don’t block your leg room with luggage underneath the seat in front of you; exercise the legs by moving them regularly while seated; walk about the cabin when you can; stay well hydrated; use compression stockings to support the circulation; sit in an aisle seat if possible.
Motion sickness is a medical consideration associated with in-flight turbulence. The following measures are recommended to minimize the risk of motion sickness: try to sit over the wing; fly larger airplanes; try to obtain a window seat and focus on the horizon; direct cool air on your face; avoid excess liquids and gas-producing foods; avoid alcohol. Although air travel can be anxiety provoking for some and alcohol can help take the edge off, it can also cause dehydration, sleep interference and on occasion “air rage,” so it is prudent to be moderate with in-flight alcohol consumption.
Decompression sickness (“the bends”) is a situation that commonly causes joint and/or muscle pain and potentially cardiovascular collapse; it typically occurs when going from a high-pressure environment to a low-pressure environment, which causes nitrogen bubbles to form in the blood and body fluids. Most people think of this happening when surfacing from scuba diving, but it can also happen on occasion during airplane ascent. Particularly dangerous is flying very soon after scuba diving.
Reference: Medical Guidelines For Airline Passengers
Aerospace Medical; Association, Alexandria, Virginia
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Tags: AED, airplane, Andrew Siegel MD, commercial flying, CPR, decompression sickness, decreased oxygen pressure, deep venous thrombosis, dryness, flying, flying stresses, gas expansion, hypoxemia, infectious disease, low cabin humidity, motion sickness, ozone, pulmonary embolism, venous thromboembolism