Most health problems in air travelers are minor, and can usually be anticipated. All travelers should know about the possible effects of reduced cabin pressure.
Squadron Leader Richard Harding is the co-author of the book Aviation Medicine, published by the British Medical Association. His research interests include respiratory physiology during flight.
Air travel is remarkably safe: it is a tribute to the technological and practical skills of aircraft designers, airlines, and air-traffic controllers that of more than 1100 million people who travelled on scheduled passenger flights during 1988, only 633 were involved in just 15 fatal accidents (excluding deaths due to deliberate acts of destruction: a cause which accounted for the loss of a further 578 lives). This level of safety has been the norm for many years and, although 1985 was a particularly bad year for aircraft accidents, 1984 was the safest year for air travel since the earliest days of flight.
Preparation for the journey
Immunizations and medicines
Even the seasoned air traveler should double-check requirements and recommendations for immunization and malaria prevention—not just for the ultimate destination, but also for any stop-over points en route.Don’t forget to carry any medical supplies you may need for the trip in hand luggage at all times, and it may also be sensible to take along a prescription or certificate, signed by your doctor, confirming the details of your medical treatment. Passengers taking regular medication (such as those with diabetes mellitus or epilepsy) should remain on ‘home time’ during a long journey, and readjust timings only after arrival.
Fear of flying
Flying is an exciting and exhilarating experience but some people may also be anxious and, occasionally, frightened by it. This is particularly likely in inexperienced passengers, although fears usually abate very quickly once they are airborne.
For the habitually fearful passenger, mild sedation may be advisable for a few days before and during the flight. Such treatment can be discussed and prescribed on a pre-trip visit to your doctor and minimizes the personal misery that can surround an impending air journey. Remember that sedatives enhance the effects of alcohol, so avoid alcohol when taking these drugs.
Once at the airport, the hustle and bustle increase tension for many people, particularly the elderly, and if at all possible a ‘dummy run’ to the airport some weeks before flying is one way to reduce this. So the is arrival in good time on the day of travel, and prompt transfer to the departure lounge, where the surroundings are usually much calmer.
The security devices through which passengers must pass in most international airports work by detecting changes in an electromagnetic held made by metal objects passing through it. The intensity of the field is set, in the UK, the USA, and other western countries at a level which will not induce changes in the electrical components of pacemakers, but machines used in other countries may not be so innocent. People fitted with pacemakers should mention the fact to security officials: this will enable a personal body check instead, and remove any possibility of interaction.
Fitness to fly
The presence of a pacemaker and indeed of any other serious medical condition should be notified to the airline at the time of booking. This useful precaution is as much for the benefit of the passenger, as for the airline and, if in doubt about whether or not to notify a condition, ask your family doctor to contact the airlines’ medical department for advice.
Patients may well be advised not to fly when suffering from a disease or condition that will be affected by the environmental changes produced by ascent to altitude. Ascent carries with it certain physiological problems, the most important of which is a fall in atmospheric pressure from 760 mm mercury (mm Hg) at sea level to about 600 mm Hg at 6000 feet (a realistic cabin ‘altitude’ for a civil aircraft, maintained by the pressurization system regardless of the actual height of the aircraft).
Airport radiation risk
A delegate at a travel medicine conference reported the recent case of a young Eskimo mother who had never flown before, traveling with an infant swaddled to a cradle-board. Airport security staff insisted on passing the unfamiliar bundle through their X-ray machine . . .
The fall in total pressure may cause problems for passengers because it allows gases in body cavities to expand. But the associated fall in pressure of each constituent gas in the air, and in particular the reduced oxygen pressure, is also highly important.
At sea level, the partial pressure of oxygen contained in the lungs is about 103 mm Hg and this pressure allows healthy individuals to function normally. At 10 000 feet, however, the partial pressure of oxygen falls to only 60 mm Hg. In fact, because of the peculiar way in which oxygen is bound to blood, healthy people are virtually unaffected by this reduction, but the health of people who have any difficulty obtaining sufficient oxygen at sea level will be further compromised by the fall in pressure, and they may develop symptoms of hypoxia (lack of oxygen).
Aircraft designers build in a safety margin which ensures that cabin altitude is held well below 10 000 feet and, as mentioned above, typically at 6000 feet, where the partial pressure of oxygen in the lungs is a ‘safer’ 74 mm Hg. If the cabin was not pressurized in this way, passengers would be obliged to breathe oxygen from face masks whenever the aircraft altitude exceeded 10 000 feet. In addition, they would be unable to enjoy any freedom of movement within the cabin. Cabin pressurization systems also allow the cabin temperature to be controlled.
Medical conditions unsuited to flying
Table 6.1 on page 224 lists many of the pre-existing medical conditions that may be affected by hypoxia and/or pressure changes associated with even the modest climb to 6000 feet. It also lists certain other conditions that should be discussed with a doctor before a flight is contemplated and about which the airline’s medical department would wish to know.
Such prior notification enables the airline to support needy passengers during embarkation/disembarkation procedures and to provide wheelchairs and escorts if appropriate. Extra seats and special arrangements may be required for those wearing large plaster casts or with orthopedic problems, or for whom a stretcher is needed. The cabin staff will also wish to know of any passengers who might need oxygen during the flight. The airlines normally make no additional charge for such supporting services, but passengers are expected to pay for any extra seats occupied.
Physiological effects of flight
Fortunately, the vast majority of passengers does not have a serious pre-existing illness and are fit to withstand the rigors of air travel. They are not, however, immune from certain other risks.
Hypoxia may affect those who are heavy smokers because carbon monoxide in cigarette smoke reduces the oxygen-carrying capacity of the blood; it may also affect drinkers (because alcohol enhances and mimics the effects of hypoxia) as well as those who are fatigued or have minor illnesses such as acute head colds. The last group should avoid or delay flying if at all possible, while heavy smokers and drinkers should avoid these vices, at least while airborne! The effects, such as acute irritation of the respiratory tract, and the effects of ‘secondary smoking’ on nonsmoking passengers, are minimized by both segregations of smokers and by efficient cabin air conditioning. By mid-1987, however, many regulating bodies (including those in Australia, Canada, and the USA) had gone further and prohibited smoking on most internal flights: a move which has met with widespread approval.
The symptoms and signs of mild hypoxia are subtle and insidious, and resemble the early stages of alcoholic intoxication: personality change, euphoria, impaired judgment, mental and muscular incoordination, and memory impairment may all be features, along with blueness of the lips, earlobes, and nail beds.
The treatment is the administration of oxygen, and this should be given by the cabin staff whenever hypoxia is suspected.
A more common, but happily less sinister, the problem is hyperventilation, which may best be described as inappropriate for breathing. The symptoms and signs of this condition are similar to those of hypoxia and, indeed, hypoxia can cause hyperventilation. But the commonest cause is emotional stress, and the picture is usually one of an obviously anxious passenger who becomes increasingly agitated, breathes rapidly, and then complains of light-headedness, feelings of unreality and anxiety (which reinforce the condition), pins and needles, and visual disturbances.
All of these features are the result of an excessive loss of carbon dioxide by over breathing and, since carbon dioxide controls the acidity of the body, this loss leads to increasing alkalinity of the tissues.
The treatment is to re-breathe the expired air (traditionally from a brown paper bag!), which will minimize the loss of carbon dioxide. Reassurance, explanation, and firm instructions to breathe more slowly should also be given. Habitual hyper ventilators may require mild sedation during the flight.
Gas expansion on ascent may manifest itself in healthy individuals by a tighter than normal waistband, particularly if much alcohol or carbonated (fizzy) drink is consumed or if gas-producing foods such as beans, brasslike vegetables e.g. cabbage, turnips, etc. and curries are eaten. Moderation in drinking and gastronomic habits is therefore advisable, and comfortable, loosely fitting clothes are recommended. (Women who are susceptible to cystitis should in any case not wear tight fitting trousers for long flights.)
Continuous plying with drinks is partly a legitimate attempt by the cabin staff to counteract dehydration caused by the dry circulating cabin air. Water or juices are the preferred means of fluid replacement because of the problems with alcohol and fizzy drinks. The dryness of cabin air may also affect wearers of contact lenses and such passengers should be aware of accelerated drying of both soft and hard lenses. Dehydration increases the risk of thrombosis, considered below.