Bohr reflex: how carbon dioxide works for you

Do you know that humans can’t survive without carbon dioxide in their blood? Sound counterintuitive? To most people, it is, and yet it’s true.

I was on a first aid course when a person asked how rescue breaths given during CPR work. They wanted to know how the breaths helped, as we use the oxygen we inhale and breathe out carbon dioxide. It was a fair question. The class understood that the patient needed oxygen to survive, but many probably believed that carbon dioxide was harmful. That’s not an unreasonable view. I remember being taught at school that humans need oxygen while plants need carbon dioxide. However, the reality is far more complex.

The air we inhale contains roughly 21% oxygen. The remainder is mostly nitrogen with a small amount of carbon dioxide. The air we exhale is roughly 16% oxygen (a little less oxygen, 14-15%, when we exercise) and around 5% carbon dioxide. So rescue breathing works because there is still oxygen in our exhalations. But the carbon dioxide that circulates in our blood isn’t just a waste gas. It’s critical to our survival.

In 1904, Danish physiologist Christian Bohr discovered the Bohr effect. What he found was that pH levels in our blood affect how hemoglobin works. Hemoglobin is the protein that carries oxygen to our cells (and makes our blood red). To carry the oxygen, hemoglobin and oxygen form a strong bond. The more alkaline our blood (higher pH levels), the stronger that bond is. Conversely, when our blood is more acidic (lower pH levels), the bond between the hemoglobin and oxygen is weakened.

This is where carbon dioxide plays a critical role. When carbon dioxide reacts with water in our blood, it forms carbonic acid and–like the name suggests–this compound increases the acidity of our blood. The result? More oxygen is released into our cells (particularly into the tissues where it is most needed). Take carbon dioxide away, then you would take away the Bohr effect. The results of that could be catastrophic. On the flip side, if we can tolerate higher carbon dioxide levels in our bloodstream, we can gain health and fitness benefits.

Look out for my next post, where I will explain about building tolerance to carbon dioxide and how that can improve your life and your fitness levels.