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For the first time, patients suffering from chronic obstructive pulmonary disease (COPD), were studied during a
commercial flight lasting almost six hours. Their blood oxygen content underwent a considerable reduction, more marked than
could have been predicted using the currently accepted guidelines. However, the oxygen reduction was generally well tolerated
by those subjects who, prior to departure, had a blood oxygen content equal to or greater than the recommended pre-flight
value.
A German team, whose study also appears in April's ERJ, conducted similar experiments on patients with cystic fibrosis. They
conclude that these patients can also travel on flights of several hours' duration without excessive risk.
What, in today's world, could be more commonplace than a plane trip lasting a few hours, whether for business or pleasure?
Yet, while such flights are unproblematic for most of us, they can be dangerous for people with certain conditions. This is
particularly true of lung disease sufferers, especially those with either chronic bronchitis (known to doctors as chronic
obstructive pulmonary disease or COPD) or cystic fibrosis. Under scrutiny, therefore, is the air pressure on board commercial
aircraft, whose passengers are subjected to a virtual altitude of 1,500 to 2,500 metres depending on the length of flight. At
such altitudes, the air contains some 30% less oxygen, a matter not to be taken lightly for patients whose blood oxygen level
is already precarious because of their respiratory condition.
For several years, doctors have been working on this issue and trying to develop recommendations, both on the minimum oxygen
level needed inside planes and on methods for identifying, in advance, patients who could encounter problems while flying.
These methods include respiratory capacity measurement and assessment of whether the subject can walk fifty metres without
getting excessively breathless. Measurement of arterial oxygen tension (PaO2) was also recommended: above a certain value, it
was deemed to indicate that the level would remain acceptable during the flight.
Real flight conditions
In fact, these various recommendations have created quite a lot of debate, especially since they partially contradict one
another.
So four Norwegian doctors decided to undertake a study in the conditions of a real flight. Their results can be seen in
April's issue of the ERJ, the scientific publication of the European Respiratory Society (ERS).
While most of the existing data came from experimental studies based either on inhalation of air with artificially reduced
oxygen levels or on time spent in a depressurised caisson, the Oslo team took an innovative approach and conducted a study on
board a real commercial flight.
The researchers decided to assess the effects of oxygen-reduced air on 18 COPD patients during a flight from Oslo to Las
Palmas (five hours and forty minutes in duration) with the cabin pressure equivalent at cruising height to an average
altitude of 1,829 metres (6,000 feet).
"The experimental nature of the earlier studies made it impossible to incorporate the various stresses that travellers
encounter during their journey: the need to carry luggage, the often lengthy trek to the departure gate, the cramped
conditions in the plane, the dryness of the cabin air, turbulence and other factors", explains Aina Aker???, the article's main
author.
"But our work has been able to include all of these elements, and we have also studied the influence of hypoxia duration by
taking measurements twice during the flight", adds Ole Henning Skj???nsberg, Aker???'s colleague at the Department of Pulmonary
Medicine of Ullev???l University Hospital, Oslo.
Rigorous selection of subjects
The Norwegian researchers set themselves two goals: to measure various parameters during the flight and to compare the values
measured on the ground before the journey with those obtained in the air.
First, they measured the various dissolved gases and the oxygen saturation in the subjects' arterial blood, noting possible
clinical manifestations, such as when the subjects moved around the aircraft cabin.
These measurements were taken twice during the flight: approximately one hour after the plane reached cruising height, and
three hours later, following a light meal without alcohol.
Aker??? and her colleagues also looked at whether certain parameters connected with the respiratory volumes and blood gases
measured prior to departure could be correlated with the data registered in-flight, and, if so, whether they allowed
prediction of what would happen during the journey.
The 18 patients (five women and 13 men, aged 49 to 73) were recruited through a lung rehabilitation centre that organises
rehabilitation programmes in warmer climates specially designed for people with chronic bronchitis or emphysema.
An important detail: the subjects selected had not suffered an exacerbation for at least two months, and all but one used
bronchodilators. Additionally, to avoid any risk of misinterpretation, they had to be clear of any symptoms that could
suggest cardiac or neurological compromise, any lung disease other than their COPD and anaemia.
Risk of fatigue after five hours
"We had, of course, made sure that the rehabilitation centre had pronounced all of our subjects fit to fly without additional
oxygen", the authors explain, "and that they could all walk at least fifty metres without excessive breathlessness, which we
verified with a treadmill test."
After an hour at cruising height, the investigators found a considerable drop in blood oxygen pressure (averaging 20%),
while, quite logically, arterial oxygen saturation had decreased from 96???1% before departure to 90???4% in-flight. This held
true while subjects remained seated; moving around the cabin caused arterial oxygen saturation to fall even more, to
87???4%.
The Norwegian team also measured arterial carbon dioxide pressure and found it to fall slightly after the first hour of
flying, in parallel with a marked rise in heart rate.
"The reduction observed after four hours of flying constitutes in our view evidence of a compensatory hyperventilation
developed by subjects to maintain their arterial oxygen saturation", Skj???nsberg comments. "This could indicate that such
patients may be at risk of respiratory fatigue during longer flights."
Comparison of pre- and in-flight data revealed a number of correlations and confirmed that arterial oxygen pressure on the
ground can allow prediction of in-flight values. However, the Norwegian team's measurements show that the current guidelines
are inappropriate.
For example, the guidelines assume that arterial oxygen pressure will be adequate if, before departure, it exceeds a certain
level (9.3 kiloPascals), yet four patients meeting that criterion had an in-flight oxygen saturation of below 84%. Five
others who met the criterion complained of mild breathing difficulties during the flight - even though they remained seated -
and eight more experienced symptoms when moving around the cabin.
The Oslo researchers emphasise, though, that the rarefaction was well tolerated by most of the patients, and only one
presented severe breathlessness at rest, which was further exacerbated during movement around the cabin.
What about cystic fibrosis patients?
The same questions apply to patients with another very disabling lung disease, cystic fibrosis, who need or wish to travel by
air. The news is good for those patients too, according to another study also published in April's ERJ.
A team from Munich University, led by Rainald Fischer, examined lung function, arterial blood gases and respiratory symptoms
in 36 cystic fibrosis sufferers under simulated air travel conditions.
Following tests in Munich (approximately 500 metres above sea level), the patients were reviewed a fortnight later after
spending seven hours in a laboratory in the Bavarian Alps, at an altitude of 2,650 metres.
As with the COPD patients, arterial oxygen pressure fell significantly at the higher altitude. A third of the subjects were
found to have values below 6.6 kPa, which is the minimum value recommended by US and British guidelines for obstructive
pulmonary disease sufferers using commercial flights.
Likewise, the German team also found that the fall was greater during physical exertion (on an exercise bicycle), but only
one patient complained of feeling unwell during such exertion.
So the German team can conclude that cystic fibrosis patients with a ground PaO2 of more than 8 kPa are perfectly capable of
tolerating, for several hours, an altitude equivalent to that found in the cabin of a commercial aircraft. Nevertheless,
Fischer and colleagues suggest to include results of spirometry (e.g. FEV1) in future guidelines, in order to emphasise the
role of bronchial obstruction in a hypoxic environment.
Which means there is no automatic reason to forbid such patients the joys of far-flung adventures.
EUROPEAN RESPIRATORY JOURNAL (ERJ), Vol. 25, No 4
erj.ersjournals
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