Some people with lung and heart disease, such as those with congestive heart failure, cardiomyopathy or chronic obstructive pulmonary disease (emphysema), may need supplemental oxygen during air travel. For anyone requiring in-flight oxygen, it takes careful planning to ensure the arrangements are in place.

"As the population ages, we're going to see more and more passengers who should use supplemental oxygen during flights," said Dr. David W. Claypool, an emergency medicine specialist at Mayo Clinic, Rochester, Minn., and medical director of Mayo's medical air transport program. "But there's no uniformity to what the airlines offer. If you require oxygen, you need to do careful checking or have your travel agent investigate and make the necessary arrangements before you book a flight."

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 mechanical problem and the cabin loses pressure.

Start at the doctor's office

Dr. Claypool's suggestion is to start with a visit to your doctor. This means you need to plan well in advance of your travel day, if you can. Your doctor can let you know what you need in terms of oxygen.

Because there is less oxygen in the pressurized cabins of airliners than there is at sea level, you might need supplemental oxygen while you're flying even though you don't need it routinely. Or, you may need a higher flow of oxygen than you regularly use. "Although aircraft cabins are pressurized, being on an aircraft is not the same as being at home," says Dr. Claypool.

Most airlines require at least 2 days' notice of your need for supplemental oxygen. One survey of air carriers found the minimal notice ranged from 2 to 3 days for domestic flights and 7 or more days for international flights. But the services may vary, so finding the right carrier for your 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. Most airlines will provide oxygen to you for a fee. The fees may range from $50 to $150 for each portion of your trip.

A few questions

When calling the airlines, ask for the medical or special services department. Here's a quick list of oxygen-related questions to ask the airlines when arranging your air travel:

• Do you accept passengers who need supplemental oxygen? What do you charge for supplying oxygen during the flight?

• Do you provide masks and/or cannula, or may I bring my own?

• What equipment will be available on my flights? What is its oxygen flow capability?

• What are my options for transporting my own oxygen tanks and/or oxygen generator? Do I check them as baggage or are they considered carry-on luggage? Is there an extra charge? Do I need to purchase an extra seat for the equipment? What is your procedure for verifying that tanks are empty?

• What documents do you require? What procedure should I follow at the airport?

Finding the right airline that can meet your needs might take some planning, because not all commercial carriers offer in-flight oxygen. Plus, there is a great variation in the oxygen devices and maximum oxygen flow rate available on each airline. If you need supplemental oxygen and don't take the time to arrange for a supply in advance, your health problem could become a serious medical emergency at flight altitudes.

You also will need to provide information to the airline. For instance, at a minimum, you'll need your doctor's name and address and a prescription that contains oxygen flow rate in liters per minute at an altitude of 8,000 feet and duration of use. You may be asked to complete specific forms, sign a liability release, or provide a letter from your doctor that authorizes you to fly, summarizes your condition and indicates any specific risks to you or others.

And once you've taken care of your in-flight needs, don't forget arrangements for when you're on the ground at your departure and arrival points as well as any airports at which you might wait during a layover. The airlines don't handle your oxygen needs on the ground nor are you allowed to take their equipment off the plane with you. Other commercial services offer oxygen service on the ground.

If commercial flights can't meet your needs or your doctor advises against it, you can inquire about air ambulance service.

Physicians who specialize in travel medicine can advise you on precautions to take before and during travel.