Myth 3. There is stale air in my lungs

 It is true that the gas composition of the air in the air sacs is significantly different to the air around us, and in fact we store two hundred times more carbon dioxide than is in the atmosphere.  Is it here because the lungs cannot expel it, or because we need it?

And if this extra carbon dioxide were harmful, then why doesn't everyone who breathe deeply would have ill health? In fact it is normally the other way around: people who are ill tend to breathe far more deeply and noisily than healthy people, whose breathing is almost imperceptible while resting.

Why do we have so much carbon dioxide in our lungs?

The reason that we need so much carbon dioxide in the airsacs is because carbon dioxide is involved in the regulation of every function in the body, and we need sufficient concentration of carbon dioxide in the lungs in order to have the correct amount in the bloodstream.

How does the carbon dioxide get there?

Carbon dioxide and water are produced when oxygen combines with glucose in the tissues to make energy. The carbon dioxide that is not required by the blood and other body parts is carried by the blood to the lungs where it moves into the air sacs.

Gases always move from places of high pressure to connected places of low pressure, and because there is almost no carbon dioxide in the atmosphere (our lungs are far from concerned about climate change at this stage), we could easily lose almost all of our carbon dioxide if the lungs were not structured in the most intricate way.

Presumably the lung structure has developed over millions of years to provide people with the best way to exchange atmospheric gases that maximise our ability to survive. Because of the special lung structure, only one seventh of fresh air inhaled reaches the air sacs. If more than this reached the lungs, extra oxygen would get into the bloodstream and extra carbon dioxide would be washed out, causing the body a major problem.

It is clear then that this 'stale' air in your lungs is not only natural, but it also keeps you alive and well.

How fresh is the atmospheric air?

 If a shaft of sunlight floods a room or a forest, it is possible to see millions of dust particles. As well as the dust we can see floating in the air there are millions more particles that are too small to see, and also invisible gases and germs. Lucky that we have a nose that is especially designed to keep these things out of the lungs where they could cause harm.