Association of Aviation Medical Examiners

The subject of aviation health continues to receive much attention in the media, with endless column inches given over to the reporting of everything from deep vein thrombosis (DVT) and cabin air quality to jetlag and cosmic radiation.

The challenge for all journalists writing on the subject of health - in this case, aviation health - is to provide accurate information without causing unnecessary and unfounded concern to the public at large.

Unfortunately, the authors of many of the pieces linking flying and health have failed to meet this challenge. If you believed some of the more lurid headlines you could even be forgiven for thinking that flying should carry a public health warning! Such selective and anecdotal reports do little to furnish the reader with the medical and scientific facts from which to make an informed and educated judgement.

Many worrying assertions continue to be made, with out reference to credible medical or scientific evidence , e.g. that cabin air quality is poor, that flying causes DVT, that cabin air circulation systems help transmit infectious diseases and so on.

It is important that the issues of flying and health continue to be given a high profile, but even more important that this profile is based upon accurate and credible information.

So what are the facts - what do we already know, where is there still uncertainty and what is being done to try and find out the truth?

Deep Vein Thrombosis

The topic that has grabbed most of the headlines is that of deep vein thrombosis (DVT), also referred to as 'traveller's thrombosis' or 'economy class syndrome'.

A DVT is a blood clot in the deep veins, usually of the leg. It is a common condition, affecting about 1 or 2 people per 1 000 every year. Some of these cases are thought to be related to long distance travel, with research estimates varying from 3% to 17%. What is clear from the research is that its not just a problem for economy class passengers, or even just air travel - DVT may be associated with all classes and all forms of long distance travel, including car, train and bus, as well as immobility due to other causes, such as prolonged sitting at a computer.

Although often very painful, a DVT is not dangerous unless pieces of the clot break off and become 'emboli' , which travel through the circulation and end up in the lungs. Large emboli can block the circulation through the lungs, causing sudden collapse and death.

Some of the causes of DVT have been known for many years. One important factor is immobility. Contraction of the muscles in the leg play an important role in keeping the blood flowing through the veins, reducing the stagnation that may allow a clot to form. However, immobility in itself is not enough to cause a DVT and most people who get one will have some other risk factor, such as underlying cancer, recent trauma or surgery, or hormone therapy, such as 'the Pill' or HRT.

World Health Organisation research

What we don't know is whether air travel is itself an additional risk factor, or whether the association is simply due to immobility, and what can be done to reduce any risk. It is to answer this question that the World Health Organisation (WHO) has sponsored a major research initiative, the WRIGHT study, which is being funded by the UK Government and the European Commission and supported by the airlines through their trade body, the International Air Transport Association (IATA). The study is now under way and should deliver its findings in 2 to 3 years. In the mean time, what should travellers do to reduce their risk?

Reducing the risk of DVT

Given the known association with immobility, it makes sense to keep mobile by doing in-seat exercises and walking around the cabin when it is safe to do so. There is also some evidence that compression stockings may help - but they must be the right size and type to provide the correct level of support. Not all so-called 'flight socks' will be effective, so take advice from your doctor or pharmacist. Those who already have factors that put them at higher risk should consult their doctor , as they may need specific medication.

Many people, including some doctors, recommend that you take a small dose of aspirin. In fact, although we know that aspirin can help to reduce the risk of heart attack in high risk groups, the balance of evidence suggests that it does not help to reduce the risk of DVT. It can also cause serious side effects in some people, so don't use it without at least discussing it with your doctor.

'Avoid dehydration' is another common piece of advice. Again, there is no evidence that this reduces the risk of DVT - but dehydration can add to the problems of travel fatigue, so it still makes sense to limit your alcohol intake and ensure that you maintain a normal fluid intake of water or fruit juice.

Cabin Air Quality

Another issue that has attracted increasing amounts of attention is whether the quality of the air that you breathe in the cabin is good enough and whether it is associated with an increased risk of spreading infection, such as TB or 'flu', particularly on aircraft where some of the air is re-circulated.

All aircraft manufacturers have to ensure that the ventilation, or 'cabin conditioning', systems fitted to their aircraft satisfy regulatory standards, which cover factors such as maintenance of an adequate cabin pressure, and therefore oxygen level, and sufficient air flow per passenger for ventilation (it takes far more air to meet ventilation requirements than to maintain the oxygen level). In turn the airlines must operate the aircraft systems in accordance with the manufacturer's specifications - on most modern aircraft the system is controlled automatically.

The pressurised cabin

One function of the cabin conditioning system is to pressurise the cabin to a level where the oxygen level is sufficient to comfortably meet the needs of both passengers and crew. Most modern aircraft are pressurised to a level of around 7,000 to 8,000 feet at their cruising altitude, an altitude lower than many skiing resorts and even some cities - Mexico City, for example, is at an altitude of 7,500 feet. The 'thin' air at this altitude can cause problems for people with some medical conditions, such as chronic lung or heart disease and these people should contact their doctor or the airline medical department before booking their flights. In most cases they will be able to travel safely, using supplementary oxygen which can usually be arranged for a small additional cost.

Transmission of infectious diseases

Most respiratory infections are spread by 'droplet spread', where the bacteria or viruses that cause illness are carried on tiny drops of moisture when a person with the infection coughs or sneezes. The closer you are to the person when they cough, the more likely it is that you will catch the bug, but the same applies if you are next to someone on the Tube, in a cinema seat or the doctor's waiting room. There was a good reason for your parents teaching you to always cover your mouth when you cough or sneeze.

On an aircraft, large numbers of passengers are seated quite closely together, sometimes for several hours. Not surprisingly, if someone on the aircraft has a respiratory infection, the passengers in the adjacent seats may be at risk of catching it - particularly if it is something like a cold, which is easily spread. Other infections, such as TB, are much harder to catch. The WHO advises that the risk of a susceptible passenger catching TB from an adjacent person only becomes significant if exposure is for more than 8 hours and, even then, only if the person has 'active' TB - is coughing up lots of the TB bacteria in their sputum.

Re-circulated cabin air

Does re-circulated air cause a problem, by spreading the bugs through the cabin? Many people believe that the cabin air is fed in at the cockpit and passes down through the aircraft to eventually reach the passengers in the economy cabins at the rear. In fact, the air flow is circular, around each section, with the air fed in through vents in the cabin ceiling and extracted through vents at floor level. The portion of air that is re-circulated is passed through high efficiency filters , similar to those used for hospital operating theatres and intensive care units, and tests have shown that the level of bacteria and viruses in the aircraft cabin is similar to that found in most offices and on other forms of public transport.

A recent study, published in the Journal of the American Medical Association compared a group of passengers who had travelled in aircraft with re-circulation and a group who travelled on aircraft without re-circulation. It showed that there was no difference in the frequency with which they developed symptoms of a respiratory infection in the week after travel.

Travelling abroad exposes people to bacteria and viruses for which they have no immunity and it is common to acquire infection during a visit to a foreign destination. Because of the incubation period, symptoms may not appear until the flight home or until the traveller has returned home. It is not surprising that the symptoms are often blamed on the flight whereas, in reality, the infection was more likely to have been acquired before the flight was even boarded.

Low humidity/dehydration

Another issue of concern for many people is the low humidity levels in the cabin air and it is often said that this causes passengers to become dehydrated. At the cruising altitude of modern jet aircraft, the outside air has no moisture content at all - indeed one of the benefits of re-circulating some of the air is that it helps to preserve the humidity produced as a result of moisture in the air that you breathe out.

The amount of moisture that is lost as a result of breathing in such a dry atmosphere amounts to about 100ml - a glass of water - over an 8 hour flight and the body's normal control mechanisms can easily cope with this by adjusting the concentration of urine produced. This was demonstrated in research published in the journal "Travel Medicine International" in 1998. One factor which can cause dehydration is alcohol and it makes sense to limit your alcohol intake both before and during flight and to ensure that you drink an adequate amount of water or fruit juice.

However, the dry air can create a sensation of thirst, by causing dryness of the mucous membranes of the mouth and throat, and some people may also experience dryness of the skin and eyes. The use of moisturising creams, lip balms and lubricating eye drops can counteract these effects, but those who wear contact lenses may be better to remove them when travelling on longhaul flights.

Jet Lag

So, reassured that you should come to no harm during your flight, you arrive at your destination only to face jet lag. What is jet lag and why do we get it?

Many of our body functions, such as sleep, performance, digestive functions and even body temperature, are affected by natural 'circadian' rhythms. The most obvious factor in controlling these rhythms is the normal 24 hour cycle of light and dark, but other factors include work/rest cycles and social interactions.

The circadian 'clock' cannot immediately adapt to changes in these factors. Jet lag is the consequence of crossing time zones rapidly, with the resultant disruption of our circadian rhythms, and is often compounded by fatigue resulting from sleep loss.

How quickly you adapt is affected by the degree of change and how old you are, but there is also marked variation between individuals. For example, most people adapt more quickly when they travel in a westwards direction, but a small percentage of the population adapt more easily to eastwards travel. Its worth remembering that you only cross time zones when you travel east or westward. If you travel from north to south, or vice versa, for example from the UK to South Africa, you can travel a long distance without having to accommodate much of a time zone change.

There is no quick and easy answer to the problem of jet lag. As the American author, H L Mencken, said, "There is always a well known solution to every human problem....neat, plausible and wrong". There is certainly no evidence that consumption of carrot juice or other special diets is helpful.

For those who are only on short trips, lasting 3 or 4 days at most, it is often better to try and stay on 'home time'. In this situation, use of the body's natural cycle of alertness and sleepiness can be used to advantage in planning business meetings and when to sleep - we tend to be most alert around 8-10 am and 8-10 pm, and most sleepy at around 3-5 am and 3-5 pm. Naps are a very useful way of catching up with missed sleep, while caffeine in coffee or colas can be very useful when you need to maintain alertness. A cup of coffee takes about 15 minutes to have an effect and this will persist for about 3 to 4 hours.

It is often said that exposure to daylight is important, but the timing of this is crucial, depending on the direction of travel and the time of arrival. In general, if you travel westwards, exposure to daylight will help to 'extend' your day and bring you into line with the local time. Don't be tempted to stay up late on your first night, as you will inevitably wake up early the next morning, when your body clock reaches that alertness peak of 8 am in 'home time'.

The use of the hormone 'melatonin' is also widely advocated, but there is still considerable uncertainty about when it should be taken, at what dose and also of its possible long term effects. If you do use it, you should be careful when buying the product, as there are often no controls on its production and samples have been shown to contain impurities.

Where Else To Find Information

It is impossible to cover in detail all of the issues that will be of interest to travellers in a short article. For those who wish to explore this further, the internet is now a particularly powerful source of information, but it is often difficult to sort out which sites are reliable. The following list gives some examples of sites which provide useful and accurate information:

Government & Regulatory:

House of Lords Science & Technology Cttee report on 'Air Travel and Health'
Dept. for Transport aviation pages - covering government action on a range of topical issues
Dept for Health - advice on travel-related Deep Vein Thrombosis
Foreign & Commonwealth Office 'Travel' pages - give extensive, regularly updated information on all travel issues, including health risks and services
UK Civil Aviation Authority - focus mainly on safety issues
US Federal Aviation Administration - has range of information for travellers, with focus on safety issues
US 'National Center for Infectious Diseases' - extensive and frequently updated information on traveller's health
World Health Organisation - extensive information on travel health

Aviation Medicine Organisations:

Aerospace Medical Association - a US-based international professional organisation in the fields of aviation, space and environmental medicine; publishes medical guidelines and useful tips for air travellers
Association of Aviation Medical Examiners - a UK educational charity promoting education and research in aviation medicine

Airlines & Aircraft Manufacturers

Boeing cabin air information - easy to follow information on cabin air systems and quality, including 'facts and myths'
British Airways travel health information - wealth of information on health aspects of air travel, covering planning, during and after your flight

AAME RESPONSE TO JAMIESON CONSULTATION DOCUMENT: RESPONSIBILITIES FOR AVIATION HEALTH

1.9. Views are sought on the various issues raised in this consultation and in particular on the following questions:

a) Do you agree that we should clarify the allocation of responsibilities within Government for issues relating to air passenger and crew health, identifying where specialist expertise and responsibility should lie?

The Association's remit as an educational charity leads us to strongly support the establishment of an authoritative body, able to provide independent, authoritative advice to air passengers and crew on for aviation health issues and, where necessary, to lead new research.

Most of our members are Aviation Medical Examiners (AMEs) for the UK CAA and, as such, are familiar with having to work within the regulatory framework of the JAA (whose responsibilities will eventually be taken over by EASA). Given the regulatory structure, it might be sensible for any new body to have a European, rather than UK only, remit.

However, given the time generally required to obtain agreement on a European level, the UK Government may wish to take the lead in setting up an appropriate organisation in the UK as a first step.

b) If so, do you agree that DfT and DH should retain top level, strategic policy responsibilities?

The Association does not have a view on the organisation of top level policy responsibility, so long as the decisions that are made are evidence based and not a matter of political expediency.

c) Below the strategic level, what detailed responsibilities should a specialist unit have?

The new body, should have the following responsibilities for aviation passenger / crew health and safety:

(a) assisting (EU) Government Departments to provide considered advice to Ministers on the development of policies and their reporting to Parliament;

(b) providing advice to industry, consumer groups and other interested parties for the benefit of passengers and crew;
(c) investigating potential new aviation health & safety concerns;
(d) managing research;
(e) providing technical input into international organisations;
(f) maintaining good relations with the aviation industry on aviation health & safety matters;
(g) identifying possible regulatory standards and making recommendations to Government;
(h) preparing the texts of draft regulations; and
(i) implementing and enforcing regulations.

i.e. responsibilities as suggested in the document, although not necessarily in the order of priority suggested.

d) Which organisational option do you prefer?

The Government's preferred option of the CAA as the lead seems sensible. The CAA's current aviation medical expertise is primarily in the area of flight crew fitness / safety to operate. There would be a need to ensure that expertise in the wider areas of aviation health were available, either through appropriate recruitment or on a consultancy basis.

In the event that responsibility for aviation health and safety were established at a European level, e.g. EASA, it would be expected that the CAA would have responsibility for application of the policies within the UK.

e) How should your preferred organisational option be funded?

The Association's remit is to support aviation medicine education and research, to the benefit of passengers and airline staff. We do not have a view on funding.