One of Cable’s professional interests is “hypoxia physiology at altitude” and training military and civilian aircrew in hypoxia awareness.
“In an otherwise healthy person, hypoxia is not a noticeable effect at cabin altitudes of 4,000, 6,000, or even 8,000 feet, which is the absolute maximum,” he says. “But those with underlying medical conditions, such as arterial or lung disease, may have impaired respiratory function.”
“As airplanes fly better and better for longer and longer, it is important to realize that there are stresses in the cabin environment and that these can interact with existing health issues,” says Professor Cable.
“Anemia or low iron can mean that the blood cells are not carrying oxygen well enough and symptoms of mild hypoxia can become noticeable, making the person a bit tired, short of breath with headaches or brain fog,” Cable adds. “Mild hypoxia also affects sleep architecture, impacts the taste of food, and exaggerates the effects of alcohol. This is another good reason to limit alcohol, beyond the associated risks of immobilization and DVT.
Airlines are aware of these risks, and Cable says Qantas has done extensive research into ways to mitigate the effects of prolonged confinement, immobilization, exposure to lower air pressure and mild hypoxia (low tissue oxygen) in the cabin.
Planning for Success at ULH
“If I can afford it, I travel for business, so I can stretch and sleep to alleviate jet lag. I adapt my sleeping habits to my new time zone, take my own pillow, noise canceling headphones and drink lots of water,” says Cable. “I limit myself to a glass of champagne when boarding and a glass of wine at dinner. An aisle seat means I don’t bother anyone when I get up frequently and walk up and down.
When he arrives, he exercises and spends a lot of time in full sun to adapt a little more quickly to the new rhythm. If he has the possibility, he will choose to travel west, which will lengthen the day and make the adaptation a little easier. Eastward compresses time zones. The evidence for melatonin is conflicting, but he says there’s enough to suggest it works somewhat for circadian dysrhythmia.
A multitude of bodily functions are keyed to circadian rhythms and because ULH can occupy almost an entire circadian cycle, airlines are constantly looking for better ways to manage the resulting disruptions and discomfort. Qantas, for example, relies on advice on many fronts ranging from cabin lighting, heating and hydration to meal times and menus.
“For those in economy or premium economy, ULH is more of a challenge. They should consider airline instructions on how to ease the constraints,” Cable says.
And some planes are better configured for ultra-long range than others. “Boeing’s 787 Dreamliner is designed to fly with a lower cabin altitude, which is better tolerated, and has higher cabin humidity, so it doesn’t have the same drying effect as other aircraft.
“It’s made from much lighter composites, which means it can be pressurized to a higher degree, which has less impact on physiology. It’s also an all-electric aircraft, so the pressurization system is a completely separate system. Usually cabins are pressurized from air coming from an engine.
“In general, these wide-body aircraft have lower passenger numbers on long-haul fires, with more business and premium allowing for more headroom and legroom.”
COVID-19 and ULH
Cable thinks concerns about COVID-19 “have been somewhat exaggerated.” So does Nader Abou-Seif, president-elect of the Australasian College of Aerospace Medicine. “But we still have to be careful with travel because there is always potential for infection and new variants,” he says.
As social distancing is non-existent on a plane – people are always within 1.5 meters of each other in business – he advocates wearing a mask, regardless of the rules.
“Apart from discomfort, masks don’t affect oxygenation or make a significant difference to blood gases,” he says. “While air filtration in planes is very effective and can certainly protect you from someone in the back of the plane, it will not protect you from the person sitting next to you.
“I’ve had patients traveling with a baby. They wore masks, the baby did not. A passenger behind them coughed the entire flight and the baby contracted COVID-19. Of course, the parents got it a few days later.
Dr. Abou-Seif, who is clinical director of aerospace medicine at the Health Reserves Air Force (for the RAAF), says it’s not a good idea to wear the same soggy mask all the way.
“On most of these flights, the oxygen concentration in the lungs is probably two-thirds of what it should be at sea level. Cardiovascular and respiratory symptoms compensate for this in healthy people,” explains Dr Abu-Seif.
“It’s easier to transmit an infection through a moist mask because you’re exhaling humidified air. Ideally, masks should be changed several times during the flight. Maybe airline staff should offer them at regular intervals.
When it comes to hydration, he says, if mucous membranes dry out a bit, the protection they provide may be less effective. Heavy smokers and travelers with underlying medical conditions affecting oxygenation, such as heart disease or obstructive airways, may have more difficulty on long flights.
“On most of these flights, the oxygen concentration in the lungs is probably two-thirds of what it should be at sea level. Cardiovascular and respiratory symptoms compensate for this in healthy people,” says “Lack of sleep is also a problem. If you’re awake for 18 hours, that equates to a blood alcohol level of 0.05 in terms of coordination and judgment.”
While the detrimental effects of ULH travel may be more pronounced in older adults, he says older travelers may be able to compensate with strategies they have personally developed over years of flying.
Airlines also have strategies. For example, Qantas expects future ULH flights to incorporate wellness zones where everyone can go to move, stretch and hydrate.
As comfort is also a function of mental state, it helps ease anxiety on board by communicating well about what to expect and how the flight will go.
