[water bubbling] - [Narrator] Whether it be jumping or diving in a lake or pool, going down to retrieve a toy off the bottom, or even pretending you were a creature of the deep.

[sinister music] Well, that just means going underwater is part of your personal experience.

But you know if you go too deep, your ears start to hurt from the water pressure, and you start to run out of air, so you swim back to the surface as fast as you can.

- [Researcher] 30 seconds.

- [Narrator] It's all about pressure and oxygen, and that's what they study here at the Duke Department of Hyperbaric Medicine, where researchers look at how oxygen moves through the body, the blood flow, and how the environment impacts how tissues react.

And what's also here is a Duke hyperbaric chamber.

It's the only civilian one of its kind in the country certified by the US Navy, and where they study how pressure can be used to treat patients.

It's led by Dr. Richard Moon.

- We treat patients with hyperbaric oxygen.

We treat emergencies, and also people with chronic problems, certain types of chronic wounds.

- [Narrator] These giant tubes can be sealed where staff can regulate pressure to simulate either an increase or decrease of it, depending on the need.

A patient sits inside the chamber, which is basically identical to a hospital examination room.

But how does pressure actually affect you?

[water splashing] You might even think scuba divers have it made because they take oxygen done with them, but even divers need to be careful.

That water pressure you felt in the pool affects a diver's entire body.

The deeper the dive, the higher that pressure is that their bodies feel under the massive weight of the water, and if they come up too fast, they can get what's called decompression sickness.

That's when nitrogen builds in the blood and creates bubbles.

In the old days, they used to call it bubble disease.

These days, some call it the bends, more on that in a minute.

- Hyperbaric medicine evolved because of diving, and back in the 19th century when people were exposed to pressure, either working in tunnels or bridges in a compressed air environment or diving, they found that when they came back to normal pressure, they often had illness.

[oxygen hissing] - [Narrator] Scuba divers call them safety stops, where they hang for three to five minutes every 15 feet on their way back to the surface.

That gives their bodies extra time to release that nitrogen buildup that happened during the dive.

[mechanism whirring] But we're not just talking about water.

It turns out that depth alone increases pressure, and you can experience that underground too, [lively music] and that's what workers building the Brooklyn Bridge discovered back in the 1870s.

The bridge was so massive, workers needed to settle the foundations of it around 78 feet in the ground under the river.

They used what are called caissons, which were developed in France, and where a bottomless chamber was lowered for workers to dig out the mud and sand.

Air was pumped down, and that, you guessed it, created pressure.

But when they came up and out after their shifts, many had serious problems, they would bend over in pain.

In fact, that's how the bends became a term.

- Some of 'em couldn't walk, and actually, there were many people who died of decompression illness.

Many of the men, it was men in those days, who went back into the compressed air environment found that their symptoms got better, and so the notion of using pressure to treat bubble disease came about.

[jet whooshing] - [Narrator] Now let's think about what happens when air pressure decreases.

Yes, you can get sick going up as well.

Oxygen molecules start to spread out because there's no pressure, and that means no usable oxygen to breathe, and there's a risk of what's called hypoxia.

- [Dr.

Moon] Most people can go to altitudes of 10 to 15,000 feet without really any problem.

At 18,000 feet, you start maybe developing a little symptom of not quite feeling right.

At 25,000 feet, there's a potential to lose consciousness.

- [Airline Announcer] Ladies and gentlemen.

- [Narrator] That's why airplane cabins are pressurized, and why flight attendants do that oxygen demonstration every time, because if a window were to blow out while the airplane is at altitude, you only have a short period of time to grab that oxygen mask before losing consciousness.

- [Astronaut] I'm halfway inside the docking compartment.

- [Narrator] Astronauts in particular need training if something unexpected happens.

In the past, astronauts from the SpaceX program needed a training ground to learn what happens in a low oxygen environment, so they were taken up to 25,000 feet inside the chamber.

- What we did with them, we had one of those little balls with different shapes in, it's for children where the child has to pick the right shape and put it in the right shape hole, but at 25,000 feet after, you know, a minute or two of hypoxia, each of the individuals we took there was having difficulty.

- [Narrator] But treating patients is the primary goal here who are suffering from things like bacterial infections, hypoxia, and carbon monoxide poisoning.

It's called oxygen therapy.

- What the oxygen does is it competes with carbon monoxide for all of the proteins that carbon monoxide attaches to, and it displaces it so that it's exhaled into the air.

[oxygen hissing] - [Narrator] Inside the chamber, the patient receives 100% oxygen through what they call a head tent like this one.

The patient breathes the oxygen while the pressure increases.

- We have the ability to monitor the patient exactly as they would be in the ICU.

We can connect the patient's arterial line electrocardiogram to the hospital monitor, which then collects the data, and stores it just as it would as if they were in a normal ICU room.

- [Narrator] It's learning how the human body reacts to different environments that's critical in helping staff understand the doorways in the treatments, and a better ability to not just help patients recover from illness, but shed light onto prevention.

[compelling music]