Download The Bohr Effect: The delivery of oxygen from the blood to the

The Bohr Effect: The delivery of oxygen from the blood to the muscles
and organs
One of the fundamental elements of the understanding the replenishment of oxygen during physical
excursion is in turn to understand the so-called Bohr effect – the way in which oxygen is released
from red blood cells and delivered to the muscles. This exchange forms the core of unlocking your
body’s true potential when it comes to sport and exercise, allowing you to raise your game and
achieve the results you really want.
The Bohr effect was discovered in 1904 by the Danish physiologist Christian Bohr. In the words of
Christian Bohr, “The carbon dioxide pressure of the blood is to be regarded as an important factor
in the inner respiratory metabolism. If one uses carbon dioxide in appropriate amounts, the oxygen
that was taken up can be used more effectively throughout the body”.2
Over-breathing is detrimental to the release of oxygen from the blood, and in turn affects how well
our muscles are able to work. Author of the book “Respiratory Physiology”, John West tells us that
“an exercising muscle is hot and generates carbon dioxide, and it benefits from increased unloading
of O2 [oxygen] from its capillaries.”3
In simple terms: haemoglobin is a protein found in the blood, and one of its functions is to carry
oxygen from the lungs to the tissues and cells. The crucial point to remember is that haemoglobin
releases oxygen when in the presence of carbon dioxide. When we over-breathe, too much carbon
dioxide is washed from the lungs, blood, tissues and cells. This condition is called hypocapnia and
strengthens the bond between oxygen and haemoglobin, resulting in reduced oxygen release and
therefore reduced delivery of oxygen to tissues and organs. With less oxygen delivered to the
muscles, they cannot work as effectively as we might like them to and leads to Lactic acid. The
urge to take bigger, deeper breaths when we hit ‘the wall’ during exercise does not provide the
muscles with more oxygen but effectively loses carbon dioxide and reduces oxygenation.
In contrast, when breathing volume remains nearer to normal levels, the pressure of carbon dioxide
in the blood is higher, loosening the bond between haemoglobin and oxygen, meaning that there is
a greater delivery of oxygen to the muscles. The better we can fuel our muscles with oxygen during
activity, the longer and harder they can work, and the lower lactic acid levels will be.
The Bohr effect can be illustrated using the oxygen disassociation curve above, which plots blood
oxygen saturation on the vertical axis against the amount of oxygen in the blood on the horizontal
axis. Within the red cells are proteins known as haemoglobin which contain iron. One of the
functions of haemoglobin is to carry oxygen from the lungs to the tissues and The Bohr effect can
be illustrated using the oxygen disassociation curve above, which plots blood oxygen saturation on
the vertical axis against the amount of oxygen in the blood on the horizontal axis. Within the red
cells are proteins known as haemoglobin which contain iron. One of the functions of haemoglobin is
to carry oxygen from the lungs to the tissues and cells of the body where it is released in order to
burn nutrients for the production of energy. Oxyhaemoglobin saturation on the vertical axis refers
to the percentage amount of haemoglobin which is occupied with oxygen. The normal saturation of
haemoglobin with oxygen is between 95 to 99%, attributable to silent and barely noticeable
breathing during rest.
When you breathe more than your body requires, carbon dioxide pressure is reduced, which in turn
causes pH to change towards alkaline. This alteration shifts the S-shaped curve on the graph to the
left and results in oxygen sticking to haemoglobin. With less oxygen being released, the percentage
saturation of oxygen in the blood is higher.
Dilation and constriction of airways and blood vessels
Breathing too much can also cause reduced blood flow. For the vast majority of people, two
minutes of heavy breathing is enough to reduce blood circulation throughout the body, including
the brain. In general, blood flow to the brain reduces by 2% for every 1mmHg decrease in carbon
dioxide.4 (a normal level is 40mmHg). A study by Gibbs to assess arterial constriction induced by
hyperventilation found that blood vessel diameter reduced in some individuals by as much as 50%.5
Most people will have experienced constriction of blood flow to the brain resulting from a period
spent over-breathing. It doesn’t take very long to feel the onset of dizziness and light-headedness
from taking a few big breaths in and out, breathing heavily through the mouth. Similarly, many
individuals who sleep with their mouths open may find it difficult to get going in the morning.
Regardless of the amount of time spent sleeping, they are still tired and groggy for the first few
hours after waking. It is well documented that habitual mouth breathing during waking and sleeping
hours results in fatigue, poor concentration, reduced productivity and a bad mood. 6-12 Hardly an
ideal recipe for quality living.
The same can also be true of individuals whose occupations involve considerable talking, such as
school teachers or salespeople, who are only too aware of how tired they feel following a day of
work. This is not necessarily due to mental or physical stimulation, but is more likely due to the
effect of increased breathing during excessive talking. Increased breathing without a proportionate
increase in metabolic activity results in a loss of carbon dioxide and reduced blood flow.
Depending on genetic predisposition, the loss of carbon dioxide in the blood can also cause the
smooth muscles of the airways to constrict, resulting in wheezing and breathlessness. A study by Dr
van den Elshout from the Department of Pulmonary Diseases, University of Nijmegen, Netherlands
explored the effect on airway resistance when there is an increase of carbon dioxide (hypercapnia)
or a decrease (hypocapnia).13
Altogether, 15 healthy people and 30 with asthma were involved. The study found that an increase
of carbon dioxide resulted in a “significant fall” in airway resistance in both normal and asthmatic
subjects. This simply means that the increase of carbon dioxide opened the airways to allow a
better oxygen transfer to take place. Interestingly, individuals without asthma also experienced
better breathing.13
The experience of excessive breathlessness and the inability to take a satisfying breath is
experienced by many athletes, including those without a history of asthma. My aim is to prevent
Hyperventilation not only amongst athletes but to the many who suffer a whole range of diseases
and poor performance as a result.
The regulation of blood pH
In addition to determining how much oxygen is released into your tissues and cells, Carbon dioxide
also plays a central role in regulating the pH of the bloodstream, how acidic or alkaline your blood
is. Normal pH is 7.365 and this level must remain within a tightly defined range or the body is
forced to compensate. For example, when the pH becomes more alkaline, breathing reduces to
allow carbon dioxide levels to rise and restore pH. Conversely, if pH of the blood is too acidic, as it
is during the over-consumption of processed foods, breathing increases in order to offload carbon
dioxide as acid, allowing pH to normalise. Maintaining normal blood pH is vital to our survival. If pH
is too acidic and drops below 6.8, or too alkaline and rises above 7.8, the result can be fatal. 14
The scientific evidence clearly points to the fact that carbon dioxide is an essential element in
regulating our breathing, optimising blood flow and releasing oxygen to the muscles, and
maintaining correct pH levels – all of which are essential for improving sporting performance,
endurance and strength. We have also seen how over-breathing can negatively affect the amount of
CO2, which can in turn limit our ability to exercise effectively and, in some cases, lead to health
issues and injury. Knowing how your respiratory system works, and the important role carbon
dioxide plays in its efficiency, allows you to maximise your potential when exercising.