If the out-breath is wrong, then the in-breath is wrong, too.
These are the words of wisdom I have read in some book many years ago and this is all I can remember from that book. But it is enough for me.
It is through breathing that we oxygenate the bodies. However, for most effectiveness we need to use the whole lungs. Of course, it is not necessary to do this all the time, but as required. For example, when doing some exercise or hard manual work.
For the out-breath (exhale) to be correct, you need to make sure that you expel all the air from the lungs. You can do this by squeezing the last bit of air out of the lungs by using your diaphragm. Easiest way is to squeeze your stomach as well. Then hold for a few seconds and let the inhalation take care of itself. It will be correct and deeper than normal.
Breathing, for most, is automatic but can be influenced consciously. By being automatic it tends to degenerate to shallow, chest type breathing. This usually happens because of stress, but also other factors like posture, tight clothing, obesity etc. That’s why we need to consciously realign it back to natural.
Through breathing we get rid of carbon dioxide and replenish the fresh supply of oxygen. Oxygen is needed by all cells in the body and there is a theory postulated by Otto Warburg back in 1930s that cells starved of oxygen can turn cancerous.
There is however, a little more to all this. Haemoglobin, or red blood cells, carry the oxygen molecule to the cells and they need to release it there and pick up a molecule of carbon dioxide. Sometimes they may not do that and will carry the same oxygen molecule back to the lungs.
The important factor here is carbon dioxide. The hemoglobin will release the oxygen molecule only when there is a certain partial pressure of carbon dioxide gas in the blood. In other words, there has to be a build up of carbon dioxide before it triggers the red blood cell to release the oxygen.
When the breathing is fast and shallow we never get a chance to build up enough carbon dioxide. Only when the breathing is slow and there is a pause after the exhalation, there is some carbon dioxide building up.
Whales can hold their breaths for over an hour while humans can only do it for a few minutes. But whales have oxygen conversion of close to 90% efficiency while humans average only 15%.