What causes us to inhale?

Answer 1

The respiratory system is a fascinating and complex mechanism that operates on a very specific criteria. BUT, the same mechanism that helps healthy people to breathe is the same mechanism that can kill someone who has Chronic Obstructive Pulmonary Disease such as Emphysema. If you think about that statement, you're probably wondering how both parts can be true. Let me explain.

In healthy people:

We breathe in air. Way down deep in the lung lobes we have aveoli, which look like a bunch of grapes still attached to the stem. There, oxygen is taken into the bloodstream. At the same time, we release carbon dioxide.

In between each breath, many activities are going on in the body, especially with the circulatory system and also at the cellular level. As the oxygenated blood moves back through the heart and is sent out through the body, the last oxygenated blood has already been delivered to all parts of the body. But, as the "old" blood returns to the heart, it has collected more carbon dioxide.

In a healthy person, the mechanism that causes us to inhale is when the brain registers the high content in the blood of carbon dioxide. The brain then signals the muscle, and most specifically the diaphragm, to move. The movement is the mechanics of breathing, but we first need the trigger--the signal-- from the brain. So, high carbon dioxide triggers the brain to trigger the muscles of respiration. We inhale and exhale based on an oxygen-carbon dioxide feedback mechanism.

Note: When a person with NO lung disease is having trouble breathing or the blood oxygen stats (levels) are going too low, doctors order oxygen. Often the order is for a high rate of oxygen, such as 6 Liters per minute. But, if a person has COPD like emphysema is different--- that high of an oxygen rate would kill the COPD patient. The explanation is below.

In persons with COPD such as emphysema:

In patients with lung disease, they can't fully exhale carbon dioxide because the lung tissue is damaged. In one example, instead of the lung tissue being soft and expandable, when it's diseased it might be stiff or harder and it cannot expand as well. So more Carbon Dioxide stays in the lungs-- and in the body. Since the lungs normally can only hold so much "air", and since carbon dioxide is being retained (kept in), then the person also takes in much lower levels of oxygen in each breath. This causes blueness around the lips, if it's really bad.

Interestingly, here is where the brain and respiratory system change in a person with COPD. Instead of high carbon dioxide being the trigger that causes the person "to breathe", it's now the reverse. The body has gotten used to HIGHER levels of carbon dioxide, so if for example, someone tries to give supplemental oxygen at a "normal" rate, the COPD person can quit breathing because of too much oxygen! The brain reads the higher O2 and decreasing carbon dioxide as "you don't need a breath". So, for severe COPD patients, a doctor might order 2 Liters of oxygen (instead of 6 liters). The 2 Liters keeps the person breathing without changing or disrupting the abnormal CO2-O2 feedback mechanism that the body and brain have adjusted to once COPD is severe.

So, to re-cap the main points:

1. In healthy people, HIGH carbon dioxide (CO2) triggers the brain to order the muscles of respiration to act. The brain stem makes the person "inhale". O2 circulates outward to all body parts, while CO2 is brought from all areas back to the heart and lungs. The person exhales, and the cycle begins again.
2. However, in persons with severe lung disease, the feedback mechanism is reversed. The person's body actually begins to rely on higher CO2 and the normal feedback mechanism doesn't work correctly. If the person is given too much supplemental oxygen, it can cause the brain to NOT send the order to "breathe!" A patient with severe lung disease has adapted to living (being alive and breathing) with a higher than normal carbon dioxide level; the brain has also adapted and triggers differently.