Even in the airplanes pressure-cabin the fysiologic conditions are change compared to the conditions at the ground. At a typical cruising altitude of 11 000 metres (37 000 feet), air pressure in the cabin is equivalent to that at an altitude of 1500-2500 metres (5000-8000 feet) above sea level
As a rule you are able to travel by airplane if you can walk 50 m or take 15 steps up without symptoms.
This means without:
.Travellers with asthma are fitt for travelling in stable phase.
Travellers with dyspnoe during in exertion may rest in the air-plane and may have oxygen. Don't assume that the oxygen masks that the flight attendants point out at the beginning of each flight will cover your needs for supplemental oxygen. The oxygen masks that come out of the overhead panel can't be used for medical purposes. The masks deploy only if the aircraft has a loss of cabin pressure. Most airlines require at least 2 days' notice if you need supplemental oxygen. One survey found the minimal notice ranged from 2 to 3 days for domestic flights and 7 or more days for international flights. Services may vary, so understanding your exact needs is important. If you use supplemental oxygen on the ground, you won't be allowed to use your own oxygen equipment during the flight.
Remember to bring your medicine.
Remember insurance. Serious medical problems requiring hospitalization and/or medical evacuation is very expensive.