Re: Would inhaling increased amounts of O2 help during

Hello Jose and thank you for your question.  You asked:

Is the heavy breathing associated with exercise a direct result of 
increased need for oxygen?
Could you supplement with an artificial oxygen supply to avoid breathing 
hard when exercising?

The simple answer to these questions is yes heavy breathing associated with 
exercise is RELATED to an increased need for oxygen, but is not as a direct 
result of an increased need for oxygen.  Breathing performs two vital 
roles, it provides us with oxygen, as you have observed, but equally as 
important it removes the waste product carbon dioxide that is generated 
during the process of respiration.  It is actually the levels of carbon 
dioxide in the blood that stimulate the respiratory system to make us 
breath harder and the body is much more sensitive to increased levels of 
carbon dioxide in the blood than it is to decreased levels of oxygen. 
Therefore during exercise more carbon dioxide is produced which stimulates 
the increased rate and depth of breathing so that we get rid of the extra 
carbon dioxide.  Of course this reflex will also result in more oxygen 
being available for the blood.

There are two main regions of receptors in the body that detect carbon 
dioxide levels in the body and these type of receptors are called 
chemoreceptors.  The central chemoreceptors are found in the medulla, which 
is a fairly primitive region of the brain that has an important role in the 
regulation of breathing.  These receptors respond to increased levels of 
carbon dioxide and hydrogen ions (pH) in the fluid in this region of the 
brain.  These chemoreceptors in the medulla are responsible for about 75% 
of the response to increased carbon dioxide levels.

The other group of chemoreceptors are the peripheral chemoreceoptors.  
These are the carotid and aortic bodies found in the carotid sinus and 
aortic arch respectively.  The aorta is the blood vessel that takes freshly 
oxygenated blood away from the heart.  The aortic arch is just outside the 
heart and this detects the oxygen and carbon dioxide content of blood as it 
leaves the heart.  The carotid sinus is in the carotid artery that supplies 
the head with blood and this is therefore detecting the amount of oxygen 
and carbon dioxide that is travelling towards the brain.  These are also 
mostly sensitive to increased levels of carbon dioxide but they are also 
sensitive to low oxygen content of the blood when levels are getting very 
low and life threatening.  These are responsible for the sensation of a 
shortness of breath and the increased respiration rate that occurs at very 
high altitude where oxygen levels in the atmosphere are very low.  At this 
time breathing oxygen in beneficial, but only air that contains normal 
levels of oxygen found at sea level, increased levels of oxygen will not be 
beneficial. 

Oxygen is carried in the blood by a specialised protein called haemaglobin, 
which has a very high affinity for oxygen.  Haemoglobin works as a huge 
storage container for oxygen.  At the levels of oxygen found at sea level 
haemaglobin is completely saturated with oxygen as it passes through the 
lungs.  Therefore the blood is not able to carry more oxygen if you 
increased the amount that is in the air that is breathed in.   Therefore 
breathing air with a higher oxygen content will not increase the amount of 
work that can be done, nor will it stop the increased breathing rate that 
one experiences during exercise because, as discussed above, this is due to 
the increased carbon dioxide content of the blood, not a response to oxygen 
demands.

There is a way of increasing the amount of oxygen carried by the blood, 
which can improve performance and is done by many top class athletes to 
give them a legal advantage over other athletes who do not take advantage 
of this natural physiological phenomenon.   As I mentioned above the air at 
high altitude contains less oxygen, which can result in a shortness of 
breath.  Over time the body adapts to these conditions so that it is able 
to carry more oxygen in the blood.  It does this by producing more 
haemoglobin.  The oxygen content in the air is only sufficient to saturate 
the haemoglobin by say 70%.  Therefore if the concentration of haemoglobin 
in the blood is increased it will still only be saturated by 70% with 
oxygen but as there is more haemoglobin then more oxygen is transported and 
the body has effectively compensated for the lack of oxygen in the air.  
When the athlete returns to sea level for a while their body will contain 
this extra haemoglobin giving them a legal performance advantage.

And one final thing.  There is one circumstance when it is a good idea to 
breath extra oxygen.  If a patient is admitted to hospital with breathing 
difficulties they may be given extra oxygen because they are finding it 
difficult to saturate their blood with oxygen due to the impaired 
breathing.  This will help them to maintain adequate oxygen levels.  
However it will not help them to remove carbon dioxide but in the short 
term maintaining adequate oxygen saturation of the blood is more important.

Thank you for your question and I hope I have managed to answer it without 
confusing you.

If you are interested in finding out more about oxygen transport and 
consumption any general physiology text book should be a good source of 
information with several chapters covering the topic.

Dave Burton