system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did Iron Lungs work back in the day?

They look pretty creepy and when looking at one, it's hard to figure out how one worked to help someone breathe. How did they work? There wasn't a mask that the patient wore or anything (that I know of).
gpt
An iron lung was an attempt to copy the way the body naturally breathes. So to answer your question, we have to discuss the body a little bit. Here goes.

In your chest, you've got your lungs. Just below your lungs you have a large, flat muscle called the diaphragm. This muscle is what controls breathing. When the diaphragm flexes, it contracts to become smaller. This happens the same way as any other muscle. What is special about the diaphragm is its shape. At rest it is shaped like a large dome tethered down at your body wall. When it contracts, the dome flattens. The effect this has on your chest is that it causes the volume of the chest to increase. As this volume increases, the air pressure inside the chest decreases. As a result of this, air is sucked down your airways and into your lungs (which have the capacity to expand). This is called **negative pressure breathing** since that is what drives air into your lungs. Just as when you sip through a straw you create negative pressure in your mouth, when you breath your diaphragm creates negative pressure inside your body to pull air inside.

Iron lungs worked the same way, but because these people had lost the use of their diaphragms, the negative pressure couldn't be generated *inside* the body, so the machine caused a negative pressure *outside* the body. The pressure difference wasn't so big that it caused damage to the person, but it was enough so that the body wall, and therefore the lungs, would expand and draw air inside to allow the person to breath.