The entire premise of the training we do at Breathing Dynamics is based on the Bohr Effect. Christian Bohr, a Danish biochemist, won the Nobel Prize in 1903 for his discovery that “the lower the partial pressure of carbon dioxide (CO2) in arterial blood (pACO2), the greater the affinity of haemoglobin for the oxygen it carries” (in other words, the lower the partial pressure of CO2 in arterial blood, the lower the amount of oxygen released by haemoglobin to cells for production of energy). This discovery was named ‘The Bohr Effect’.

Restated – it is CO2 that determines how freely oxygen (O2) is released into the cells for energy production. So, rather than O2, it is CO2 that is the limiting factor in respiration potential.

Indeed, whilst we have access to 21% oxygen in the atmosphere at sea level, we only use 5% (or less than ¼) of this 21%. So we have more than enough oxygen in inspired air for our requirements. It is how we use this oxygen that is important.

Interestingly, there is only 0.03% of CO2 in the atmosphere at ground level as it is used as fuel for respiration by plants. We actually make the CO2 we use as a by-product of metabolic processes (production of energy). This is either exhaled as waste or stored in the lungs.

The role of CO2 in the Bohr Effect occurs via its role in altering blood pH. The optimal pH for uptake of oxygen from inspired air by haemoglobin in the lungs is 7.45, whilst the optimal pH for release of O2 by haemoglobin into cells in arterial blood is 7.35. Therefore a drop in pH, or increase in acidity, is required between O2 being taken up into the blood in the lungs and being released into tissue or cells.

The presence of CO2 in our lungs, and subsequently our arterial blood, allows for this change in blood pH by being converted into carbonic acid in the blood. The minimal partial pressure of CO2 required in arterial blood to allow optimal release of O2 by haemoglobin into cells (at pH 7.35) is 40mmHg. In order to achieve this minimal partial pressure of 40mmHg we need to have a residual store of 6.5% CO2 in our lungs after exhalation. This residual storage of CO2 in the lungs then permeates back into the arterial blood to affect the drop in acidity to 7.35 for optimal release of O2 into our cells.

So how do we ensure we maintain this storage reservoir of 6.5% CO2 in our lungs that enables the pH shift in arterial blood, and therefore optimal release of oxygen into cells?

By nose breathing – at all times.