Fitness For Flying

[Guest guest]

While many of us are very familiar with the concept of fitness in normal

daily life, we are not always aware of what it measn to be " fit " to fly. The

following article offers very useful information in this regard.

------------------------------------------------------------------

CRITERIA FOR DETERMINING FITNESS TO FLY

http://www.medinet.co.uk/crit.htm

Safe return of passengers to their country of origin after they become ill

overseas is achieved by an understanding of the physics of the civilian

flight environment and how it interacts with pathological changes brought

about by disease. A passenger travelling in a modern jet aircraft on a

scheduled flight was assumed to be comparatively fit by the designers of the

life-support systems on board. A perfectly safe environment would be one that

could reproduce the barometric pressure and molecular oxygen concentration at

sea-level. It would also have a comfortable relative humidity.

Aircraft design, however, is a series of compromises between weight, expense,

speed, convenience and ease of manufacture. The compressors required to

produce a sea level cabin at operating altitudes would be too heavy and too

demanding of additional fuel, and the amount of water required to return

sea-level relative humidity to the air taken from outside the cabin at -57C

would be unfeasible bulky and heavy. Thus, a compromise is reached as to an

operating cabin pressure of altitude equivalent to 7500 feet, and relative

humidity of cabin air is around 17%. The barometric pressure is around 80%

that of sea-level, which represents a volume increase of about 120-130% to

any compressible substance such as trapped air. The fall in molecular oxygen

concentration will cause a desaturation of blood oxygen of approximately 1%

in the healthy subject.

Hypobaric Conditions and Disease

The hypobaric conditions described about will cause any disease condition

which produces or traps gas to rapidly deteriorate if the patient is exposed

to them. Classic absolute contra-indications to flying are recent craniotomy

or air encephalogram, recent abdominal surgery, pneumothorax without a

thoracic drain, facial injuries with intra-sinusal haemorrhage, otitis media,

acute small or large bowel mechanical obstruction and penetrating injury to

the globe of the eye. Dental conditions where caries are full of gas produced

by the putrefaction of bacteria can give rise to severe odontalgia at

altitude, and damage to the tooth.

Flight less than forty-eight hours after deep-sea diving below 50 feet can

produce the " bends " and death even at modest cabin altitudes. The rate of

change of cabin altitude and the direction of the change (barotrauma is worse

on descent as the opening of the Eustachian tube is sucked flat by the low

pressure in the middle ear, making the immediate equilibration of pressure

more difficult) are factors in determining tolerance to pressure effects.

Hypobaric Hypoxia and Disease

Any disease with an ischaemic component will deteriorate in conditions of

hypobaric hypoxia, and recent tissue infarctions may extend. Congestive

cardiac states which are compensated at sea-level may decompensate at

altitude, often in combination with mild exertion, such as walking to the

on-board toilet. Organic/Toxic confusional states and alcoholic intoxication

are synergistic with hypoxia. The hypoxia gets worse with the time the

patient is exposed to it, as the initial hyperpnoea returns to a normal rate.

For these reasons, it is recommended that patients should not travel by air

for ten days after a myocardial or cerebral infarction in the case of

short-haul (same continent) flights and fourteen days in the event of

long-haul flights. Patients in uncontrolled cardiac failure should not travel

by air until control is achieved, and patients requiring oxygen

supplementation at sea-level should be weaned off oxygen before air travel.

All acute patients in this group should travel with supplementary oxygen

sufficient to provide intermittent oxygen at 2 litres per minute. Such

patients may also require a doctor or nurse to escort them on the flight.

Portable oximetry has made rational administration of oxygen therapy possible

even in flight.

Other Physical Factors

Traction based methods for providing acceleration, such as the aircraft

wheels during takeoff are only able to produce accelerations of 1G, and

whilst considerable acceleration is possible with a jet engine line aircraft

are exceedingly unlikely to produce accelerations which will compromise

patients. However the tilt of take-off and landing may produce severe

hydrostatic effects which will effect cardiac patients.

Statutory Requirements

These mainly relate to mobility. A patient, in order to be able to use an

airline seat must be able to seat upright during takeoff and landing, and to

get out of the seat with the minimum of outside assistance. Patients who

cannot do so, or who need to be lying can be accommodated by stretcher on a

scheduled flight, with prior arrangement of the airline and with a mandatory

attendant. In all matters of fitness to fly, the airline and the doctors

designated by the airlines have the final discretion, and the captain can

veto the decision of the airline medical department without having to give

justification.

-------------------

Dr Mel C Siff

Denver, USA

Supertraining/