Breathing air into and out of the lungs supplies us with oxygen and gets rid of excess CO₂. Air entering the lungs is oxygen rich, and the blood supply, as it passes through the lungs, picks up oxygen easily and carries it round the body attached to haemoglobin molecules in red blood cells. You can buy quiet cheaply a handy device (a pulse oximeter) that you stick your finger into and it can actually measure how much oxygen is carried on your haemoglobin (I don’t suggest you rush to buy one, results can be hard to interpret, see below). Normal oxygen saturation levels (sats) are usually considered to be between 96- 99%; people with lung damage might struggle to achieve that. However, a plentiful supply of oxygen circulating in your bloodstream and a 99% oxygen reading is not always an indicator that your body and its organs are well oxygenated. There is another step to consider;  the blood has to carry the oxygen round the body to where it is needed most and that will be where there is low oxygen – for example in an actively contracting muscle -and then the blood has to release the oxygen from the haemoglobin so it can be utilised where it is needed.  An active muscle will be rapidly metabolising and will require more oxygen, and will produce more CO₂. The higher local levels of CO₂ and the lowered local pH are important triggers that help to release oxygen from the haemoglobin so it can be used exactly where needed.  This is known as the Bohr Effect and has been described in physiology text books for a century.

The more you breathe, the less oxygen you get.

Unfortunately, hyperventilation (breathing more than you need for the activity you are doing) can cause loss of too much CO₂ from the body (hypocapnia). There is only a tiny amount in the air we breathe, so to maintain a healthy level in our bodies, we have to retain and accumulate CO₂ by breathing correctly. Breathe too much and CO₂ levels can become too low, and alter the whole body biochemisty.

When CO2 levels are too low, oxygen is not released efficiently from the blood to where it is needed. (Picture by V Lunn Rockcliffe)

One thing that can happen with lowered CO₂ is that oxygen is no longer efficiently released from the haemoglobin in circulating red blood cells in the blood supply. Instead of the oxygen being released in the body where there is high metabolic activity, and high CO₂, the oxygen sticks tightly to the haemoglobin and continues to circulate in the bloodstream, where it really can’t do any good. It is easy to see that aching muscles and brain fog and a host of symptoms could be related to low oxygenation caused by hyperventilation and unbalanced blood gases. It is very common for people to say “breathe deeply” “take big breaths for more oxygen”. In fact it is easy to get enough oxygen, air is about 21% oxygen and the cells of the body only need about 2%. Much more likely deep breathing will flush out too much CO_2, air only has 0.04% and the cells of the body need about 6%. So by trying to breathe deeply for more oxygen, you can do the opposite and starve your body of oxygen. The more you breathe, the less oxygen you get.
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