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Airlines are cutting costs – Are patients with respiratory diseases paying the price?

BARCELONA –

For patients with chronic lung disease, air travel may worsen respiratory symptoms as they are exposed to a reduced air pressure in the aircraft. Newer airplanes can fly at higher altitudes and have lower cabin pressures than older aircraft, report Leigh Seccombe and colleagues, of the Department of Thoracic Medicine, Concord General Hospital, Sydney, Australia, at the 20th Annual Congress of the European Respiratory Society.

According to regulations, commercial aircraft fly at cruising altitudes ranging up to 41,000 feet above sea level, but are pressurised to a cabin altitude of 8,000 ft (2,438 m), meaning that  the aircraft environment has a reduced pressure of oxygen, equivalent to that at 2,438 metres above sea level. The reduced alveolar oxygen partial pressure at this altitude equates to breathing air with an oxygen concentration (FIO2) of 15% oxygen (rather than the normal 21%) and lowers the Pa,O2 of a healthy passenger to 7.0–8.5 kPa (53–64 mmHg).

Healthy people tolerate the reduced amount of oxygen available but lung disease patients may need extra oxygen to help them breathe normally. Many lung disease patients already have low levels of oxygen in their blood compared with healthy subjects, so an increase in altitude is likely to further reduce the amount of oxygen available, aggravating their symptoms. Even the slightest effort, such as going to the toilet, may further reduce arterial oxygen concentration in lung patients as natural compensatory mechanisms fail.

Aircraft cabins cannot be fully pressurised to sea level equivalent for structural and economic reasons. In general, there is a fixed relationship between cabin pressure (CP) and aircraft altitude. The higher the plane flies, the lower is the cabin pressure. This relationship is known as the CP schedule and varies from one aircraft type to another. The actual CP is determined by the aircraft type and the altitude it is flying at.

Leigh Seccombe and colleagues found in a previous survey that the CP for Boeing 747 (B747) is significantly greater than the required 752 hPa minimum. This is likely to create a margin of safety for patients with chronic lung disease on long-haul flights. The B747 is progressively being replaced by the Boeing 777 (B777), Airbus 330/340 (A330/340) and A380. These planes’ actual CP characteristics during flights are unknown.

In the recent study, continuous records of CP were made during flights on B747, B777, A330/340 and A380 aircraft over 8 years using a wristwatch altimeter (Suunto X6, Finland). CP schedules relating to cruising altitude were created for each aircraft type. Median CP was calculated and converted to an equivalent FIO2 at sea level for ease of comparison.

CP was recorded on 102 aircraft flights, mean (SD) duration 9.1 (1.0) hours. Median CP in the B747 flights was significantly higher at equivalent altitudes compared to the B777, A330/340 and A380. Those for the other aircraft types were similar.  The following table shows illustrative data.

 

 

Number of flights

Median CP

CP at 34,000ft

CP at 40,000ft

Boeing 747

65

838hPa

844hPa

793hPa

Boeing 777

13

810hPa

835hPa

773hPa

Airbus 330/340

18

804hPa

831hPa

777hPa

Airbus 380

6

808hPa

835hPa

786hPa

 

 

Based on the measurements of median cabin pressure, patients flying on a B747 would be breathing approximately 17.4% oxygen sea level equivalent, vs 16.7-16.8% on the other aircraft types. “Part of this difference is related to CP schedule and the remainder related to the newer aircraft being able to fly at higher altitudes”, the researchers explain.

“The B747, for as long as it has been a dominant long-haul aircraft has provided a safety buffer to travellers because it has CP characteristics that are much better than the minimum required by regulation. These differences in CP and resultant worsening of hypoxia with newer aircraft may have an effect on those travelers with mild lung disease and may significantly impact on patients with severe lung disease who might choose to fly long-haul on a B747 for preference when this is an option.“

As the B747 is phased out, the overall risk to older patients with chronic lung and other disease can be expected to increase.

 

Abstract Number: 2270
Title: "Newer long-haul commercial aircraft have lower cabin pressure than Boeing 747."

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