He said that asthma patients, while at risk if experiencing a severe attack, should normally be able to cope. The British Thoracic Society is currently developing guidelines for doctors on how respiratory patients should be tested for their fitness to fly. The methods used by doctors vary widely - from simply asking patients to walk 50 metres and seeing if they become breathless, through blood testing of oxygen to placing them on a machine which mimics low atmospheric pressure to test their response. Each airline has its own procedures to try and spot the passengers most at risk. Virgin Atlantic has trained cabin door staff to recognise the tell-tale signs and call a doctor.
All airlines carry oxygen cylinders for use in emergencies.
Doctors, many of whom, as passengers, are called upon to help in a crisis, have expressed concern at the lack of lifesaving equipment aboard aircraft. The BBC is not responsible for the content of external internet sites.