AP Explains: ?
MICHAEL GRACZYK, Associated Press

HOUSTON (AP) — A doctor volunteering for a dog rescue operation who failed to land his small plane in Central Texas as planned and was later tracked by fighter jets flying over the Gulf of Mexico appeared unresponsive and may have been suffering from a lack of oxygen, officials said Thursday.

The condition is known as hypoxia.

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WHAT IS HYPOXIA?

Hypoxia is the condition that occurs when someone’s brain is deprived of adequate oxygen. If untreated, it can be fatal.

Oxygen pressure decreases as altitude increases. It’s the reason planes are pressurized, mountaineers carry supplemental oxygen on high-altitude climbs, or climbers and athletes train at higher altitudes to become acclimated to the lower oxygen pressure. It’s also the reason flight attendants explain to aircraft passengers the use of oxygen masks that will drop from overhead compartments in the unlikely event cabin pressure is lost during a flight.

Providing adequate oxygen resolves hypoxia.

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THE EFFECTS OF HYPOXIA

“Thinking becomes cloudy, a person can become confused, lethargic, fatigued,” according to Dr. Zeenat Safdar, a pulmonologist and director of the Houston Methodist Hospital Pulmonary Hypertension Program at the hospital’s lung center.

The person becomes discolored and dies.

“Before that, a lot of confusion,” Safdar said. “They wouldn’t know where they’re going, what’s up and what’s down. The sense of direction may be clouded.”

It also depends on where they are. At a lower altitude, it can be a gradual process.

“They want to sleep, might have a seizure, become short of breath or can’t breathe … He might not even know what’s happening.

“With a small plane, maybe their own plane, they don’t realize what’s happening,” Safdar said. “These things are very unfortunate.

“If it starts to happen, and if you get oxygen right away, you’ll recover right away. It depends on how rapidly it happens. If you go from pressurized cabin at 30,000 feet … and now the plane loses pressure, in few minutes the person is going to start noticing. If they’re not that high up, like in a small aircraft, the effect going to be more slow and more subtle and may be even missed,” Safdar said.

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HYPOXIA AT SEA LEVEL

Safdar said hypoxia is not limited to people at high altitudes.

People suffering from emphysema, chronic obstructive pulmonary disease, lung damage and the effects of pneumonia all can be described as dealing with hypoxia.

“See people walking around with oxygen tanks?” she asked. “The need for oxygen. We are treating hypoxia all the time.”

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NOTABLE HYPOXIA DEATHS

—In 1999, a charter jet crash killed pro golfer Payne Stewart and four others and flew halfway across the country on autopilot before crashing in a pasture in South Dakota. Everyone on board had apparently lost consciousness for lack of oxygen after a loss of cabin pressure and investigators said the plane crashed after it ran out of fuel.

—Among multiple theories in the 2014 disappearance of Malaysia Airlines Flight 370 carrying 239 passengers and crew is a slow or sudden decompression, causing a loss of oxygen, could have killed everyone on board. If oxygen levels dropped, a loud, automated warning would have alerted the pilots to put on their oxygen masks and immediately descend below 10,000 feet, where there is enough oxygen to breathe without aid. But aviation experts said in that case the plane should have kept flying automatically toward Beijing and been visible on radar.

—Greek investigators said pilots on a Cypriot airliner did not realize an automatic pressurization system was set to “manual” when in 2005 a loss of cabin pressure and oxygen led to hypoxia and the plane’s crash in Greece, killing all 121 people on board.