Anatomic and physiologic dead space

The main job of the lungs is gas exchange, pulling oxygen into the body and getting rid of carbon dioxide.

Normally, during an inhale - the diaphragm and chest muscles contract to pull open the chest and that sucks in air like a vacuum cleaner, and then during an exhale - the muscles relax, allowing the lungs to spring back to their normal size pushing that air out.

But as it turns out, not all the air that we breathe in, ends up participating in gas exchange.

As we inhale, air enters the nasal cavity or the oral cavity and travels down the trachea and then splits into the two mainstem bronchi and enters the two lungs.

Within the lungs, the bronchi divide into progressively smaller and smaller bronchioles until air gets down to tiny thin-walled air-sacs called alveoli which are surrounded by tiny capillaries. This is the site of gas exchange.

So, the part of the respiratory tree prior to these alveoli, starting from the nose, or the mouth, right up to the tiny terminal tiny bronchioles without these alveoli, merely acts to conduct or transport air to the alveoli. This part is known as the conducting zone and it does not take part in gas exchange.

The volume of air contained in this conducting zone is known as anatomic dead space.

‘Dead’ sounds kind of ominous but it basically reflects the fact that this air is as good as dead to the body, because you can’t extract oxygen from it.

‘Anatomic’ means that this dead space is inbuilt within the anatomy of the respiratory system and doesn’t really change; no matter what we do, we cannot ever use this air for gas exchange.

Alright, so now let’s simplify all this—so this ball represents all the alveoli, and this portion represents all of the conducting zone, in other words the anatomic dead space. So how much air is part of this anatomic dead space?