June 17, 2024 – Is there a long flight in your near future? Before you board, you might want to reconsider ordering that drink to relax or fall asleep.
When planes climb to cruising altitudes (30,000 to 40,000 feet), the pressure in the atmosphere drops, affecting the ability of oxygen to move from the lungs to the blood. (This is known as arterial oxygen partial pressure.) In turn, this affects how well the lungs move oxygen from the air into the blood when you breathe in, and remove carbon dioxide when you breathe out, as well as how much oxygen is circulating in the blood.
For most people, a 90% to 95% blood oxygen content, or saturation, is considered healthy. Commercial flights are required to maintain a minimum cabin pressure that sustains healthy blood saturation levels at 90%.
But scientists are warning that a combination of altitude, cabin pressure, alcohol, and sleep on long flights (more than 6 hours) spells trouble for adults, especially those with risk factors for certain conditions or heart and lung disease.
In a new study, researchers assigned 48 healthy people ages 18 to 40 years to either: 1) a sleep lab under normal, ambient air pressure conditions observed at sea level or 2) an altitude chamber that mimicked cabin pressure at cruising altitude.
Twelve people in each environment slept for 4 hours having consumed no alcohol, while 12 others slept for 4 hours having consumed enough alcohol to achieve a target 0.06% blood alcohol concentration (the usual limit for driving in the U.S. is 0.08%) in one night. This was followed by a 2-night recovery period and then one more night in each group, but in reverse in terms of alcohol consumption.
“After moderate alcohol consumption, oxygen saturation decreased below 90% during sleep and stayed there for some time – 201 out of 240 minutes,” said Eva-Maria Elmenhorst, PhD, a physiologist, study co-author, and deputy head of the Department of Sleep and Human Factors Research at the Institute of Aerospace Medicine in Cologne, Germany. This phenomenon is called “hypobaric hypoxia,” also known as low blood oxygen at higher altitudes.
Also, she said, the heart rates of people in the study did not decrease during sleep as they normally would, but increased to a median 88 beats per minute.
“Our concern is that individuals with pre-existing medical conditions might board a plane with already low oxygen saturation that drops further during sleep after alcohol intake, exacerbating their condition and leading to a medical emergency inflight,” Elmenhorst said.
About Hypoxia
“When we talk about hypoxia, we are essentially referring to a reduction in the amount of oxygen available for you to breathe,” said William Kent Cornwell III, MD, director of sports cardiology and an associate professor of medicine at the University of Colorado Hospital in Denver.
He said hypoxia can be caused by the environment or atmosphere (as experienced on planes) or by an internal reaction to the amount of available oxygen due to medical conditions. The way that the body responds is to increase the amount of fight-or-flight hormones.
“The worse the hypoxia, or higher in altitude you go, the more of this response you are going to have,” Cornwell said.
That will affect the heart and blood vessels, because the heart is going to work harder, causing the heart rate to increase. Your cardiac output – the amount of blood your heart pumps every minute – will also increase, he said. “Basically, what is happening is that your body is trying to compensate for the reduction in the amount of available oxygen.”
“The amount of hypoxia on a flight for most patients is fairly modest,” said Luu Van Pham, MD, an assistant professor of medicine and a pulmonology, critical care, and sleep medicine doctor at Johns Hopkins Medicine in Baltimore. “It’s really those people who have increased or decreased tolerance to hypoxia, or have worsening lung disease, that will be a concern.”
At risk are people with sleep apnea or obstructive sleep apnea, especially if they drink alcohol during the flight. Alcohol makes the condition worse; it’s been shown to reduce the drive to breathe, relax the muscles in the mouth and throat, and make it difficult to wake up, which means that breathing is obstructed for longer in people with sleep apnea who drink on planes.
In-Flight Emergencies
The CDC estimates that more than 4 billion passengers travel on commercial global flights each year, or roughly 10 million per day. One of every 604 of these flights, or 0.17%, involve medical emergencies, including fainting, heart issues, breathing problems, or nausea/vomiting.
Although this percentage is small, having an event in flight poses challenges, especially on long-haul flights. Planes carry limited medical equipment, and except for a good Samaritan passenger, they do not have dedicated medical personnel. Not to mention, “there’s not an easy place to land the plane, and the response time for emergency personnel is delayed because of obvious logistics,” said Cornwell.
Even if a plane is able to find a nearby airport, it can take as long as 30 minutes for it to descend from cruising altitude. And the diversion airport might not be able to treat medical emergencies, adding extra time in situations where every minute counts.
Word to the Wise: Don’t Drink and Fly
Frequent travelers are likely used to making a visit to a travel medicine specialist before visiting certain countries or remote locations. But the focus of travel medicine is often the prevention of infections and infectious diseases, depending on your destination; common shots target things like tetanus, yellow fever, and hepatitis B.
If you have heart or lung issues, you might consider a visit to your primary care doctor to review current medications, get extra prescriptions, and discuss dos and don’ts before you travel.
“If you have any type of breathing issues and your oxygen saturation levels are borderline, you might want to consider bringing a small portable oxygen tank for the plane,” advised David Holmes MD, a clinical associate professor of medicine and director of global health education at Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo, NY.
He said it's important to stay hydrated during the flight, regardless of health status. “Dehydration can precipitate an increase in heart rate,” he explained. This is especially true in environments such an airplane cabin – with low humidity and frequent changes in air pressure – and if you have factors like exhaustion.
Use of tranquilizers and sedatives before or during the flight might also increase the risk by placing extra stress on the heart and affecting oxygen saturation and heart rate, even more so when combined with alcohol.
Elmenhorst noted one more thing: The people in the study slept while lying down. So first-class and business-class passengers, who have easier access to alcohol onboard as well as seats that lie flat, may be at greater risk than passengers flying economy.
The solution? Don’t drink and fly.