The Bohr Effect states that in the presence of carbon dioxide, the oxygen affinity for haemoglobin decreases. In other words, an increase in blood carbon dioxide level and corresponding decrease in blood pH causes haemoglobin to bind to oxygen with less affinity.
This effect facilitates oxygen transport as hemoglobin binds to oxygen in the lungs, but then releases it in the tissues, particularly those tissues in most need of oxygen. This is because when a tissue's metabolic rate increases, its carbon dioxide production increases.
To summarise this: If we breathe within normal parameters this mechanism works very well to deliver oxygen to brain and body tissues. By contrast, over-breathing (i.e. breathing more than the physiological norm) can upset this delicate balance thereby reducing oxygen delivery to cells and potentially resulting in a range of possible compensatory mechanisms.
The hazards of hyperventilation
Anyone who has experienced dizziness or "seen stars" after a violent fit of coughing, blowing up party balloons or an air mattress will be familiar with the effect that breathing too much air has on reducing oxygen supply to the brain. If breathing large volumes of air is supposed to be beneficial, why does it make us dizzy?
Hyperventilation, or over-breathing, does not add oxygen to arterial blood. This is because under normal physiological states arterial blood is close to saturation with respect to oxygen and is simply not able to absorb more.
Normal oxygen saturation values are 97% to 98% in a healthy individual.
However, over-breathing depletes carbon dioxide in airways and arterial blood producing a condition known as hypocapnia. Hypocapnia reduces oxygen availability to our cells in two ways:
- As blood levels of carbon dioxide drop during hyperventilation, smooth muscle can constrict around blood vessels restricting the flow of oxygenated blood to the tissues.
- Lower levels of carbon dioxide dissolved in the blood shift blood pH towards a state known as respiratory alkalosis and the haemoglobin which transports oxygen in the blood binds more tightly with the oxygen reducing its release to the body tissues.
Over-breathing and cerebral hypoxia
The figure below shows how even a few minutes of over-breathing (hyperventilation) can starve your brain of oxygen. If one minute of hyperventilation can do this, imagine the toxic effect on your body from a lifetime of over-breathing.
Functional MRI scan of a human brain showing oxygen saturation of haemoglobin.
Red and yellow areas correspond to highest oxygen saturation of haemoglobin
The left-hand image shows normal oxygen saturation in a healthy breather's brain. The right-hand image shows oxygen availability in the brain is reduced by 40% as a result of about a minute of over-breathing (hyperventilation). Not only is oxygen availability reduced, but glucose critical to brain functioning is also markedly reduced as a result of cerebral vasoconstriction (from Litchfield 2003)v.
Over-breathing and its effects on health
Over-breathing can trigger asthma attacks, panic attacks, migraines and exacerbate a range of disorders including breathlessness, shortness of breath, asthma, hypertension, heart palpitations, irregular heartbeat, dizziness, spacey feelings, tingling in hands and feet, numbness, light headedness, fatigue, sleep apnoea, cold hands and feet, digestive disorders including gastric reflux, bloating, irritable bowel and stress disorders.
The scientific basis linking dysfunctional breathing to these symptoms and disorders is documented in numerous studies and medical text books and explained in our introductory seminars. Copies of published research and studies are available on request. You will also find many of these in the section for health professionals on this website.
At the Buteyko Breathing Clinic we can help you enjoy restful snore-free sleep, relieve symptoms of asthma and other respiratory disorders, reduce stress and enjoy better health and well-being by helping you change the way you breathe.
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