Why does exercise induce asthma?
So you or someone you know has a diagnosis of ‘exercise induced asthma.’ A bit of an enigma – isn’t it? After all, exercise is supposed to be good for you, but the minute you try to exercise your airway decides to close up. Why is it that something that is supposed to be good for you actually brings about harm?
Understanding why exercise is a trigger for asthma starts with understanding what causes asthma in the first place. Now if you have a diagnosis of asthma you will know that asthma is caused by over-reactive airways – airways that constrict and close down when they are irritated. And that is true. But here is the clanger – why does exercise irritate your airways? (Yeah – OK. Some of us are just irritated by the thought of exercise full stop!) But back to the story…
The answer lies in the fact that along with having the gene for over-reactive airways, asthmatics routinely breathe twice as much air as healthy people. Whereas the normal quantity of air inhaled by healthy people each minute is between 4-6 litres, asthmatics typically breathe 12-15 litres a minute, and this is imperceptible to all but the trained eye. Asthmatics are over-breathers – that is they have a dysfunctional breathing pattern. And over-breathing changes our body chemistry in ways that make us more susceptible to adverse health effects.
The number one change that happens in the human body as a result of over-breathing is lowered levels of carbon dioxide in the blood. And looking at studies of asthmatics which include blood carbon dioxide levels, this is certainly the case. Most people think carbon dioxide is just a waste gas, but carbon dioxide is essential to human life – it is a key player in the regulation of many body systems. Some of the actions of carbon dioxide that are relevant to people with asthma are:
- Carbon dioxide opens up and relaxes the airways. Lowered levels of carbon dioxide constrict the airways.
- Carbon dioxide helps suppress histamine production. Higher histamine levels cause allergy responses in the body, so there is a sense in which carbon dioxide is a natural anti-histamine.
- Carbon dioxide helps improve oxygen supply to the cells and tissues of the body. Yep – you read that right! Oxygen is transported by haemoglobin in the blood, and when the oxygen-saturated haemoglobin reaches the cells, the haemoglobin has to surrender the oxygen so that it can enter the cell. What governs whether or not the haemoglobin surrenders the oxygen is the presence of carbon dioxide (for those of you who love the technical details research the Bohr Effect, or the Oxy-Haemoglobin Dissociation Curve).
So let’s put this together. Low blood levels of carbon dioxide cause the following:
- Constricted airways
- Higher levels of histamine – causing mucus production and allergy reactions
- Poorer oxygen supply to the cells and tissues of the body causing fatigue and breathlessness.
Sounds a bit like asthma, doesn’t it?
Physical exercise does not need to cause asthma. What determines whether physical exercise induces asthma or not depends on whether the blood level of carbon dioxide rises or falls with the exercise, and the key to achieving a rise rather than a fall is to not over-breathe. Your first defence strategy to maintaining healthy levels of carbon dioxide during exercise is to exercise with your mouth closed, just like every other species of animal does. Ever seen a cheetah bolting across the savannah with its mouth hanging open? All animals exercise with their mouth closed – even race horses. Exercising with a closed mouth is not an easy transition to make, particularly if you are an avid over-breather. But persistence (and some help from a breathing retrainer if you can’t manage it on your own) will pay off with better exercise endurance.
Asthma need not be a life-long sentence. Many asthmatics have found that breathing retraining gives them better control, reduces the asthmatic symptoms and improves their exercise endurance. A number of clinical studies have shown that breathing retraining reduces the use of inhaled steroid use by up to 50% and the use of broncho-dilators (such as Ventolin) by 70–90% along with better symptom control and an improved quality of life. Many find that they no longer need medication to control their asthma.
If you would like to learn more about:
- managing asthma through breathing retraining
- undergoing capnography testing to find out whether your carbon dioxide levels might be low
- improving your exercise endurance
contact Buteyko Vitality.