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Dr Les Ansley from Sport Asthma and Northumbria University talks exercise-induced asthma

Exercise-induced asthma (EIA) describes a condition in which the airways narrow in response to exercise, which makes it more difficult to breathe air out of the lungs. EIA occurs in most people who have clinical asthma but also a large proportion of people who are otherwise ‘healthy’. EIA is especially common in athletes and some estimates suggest up to 50% of athletes may be affected.

However, accurate diagnosis of EIA is difficult because somewhat surprisingly symptoms that might be associated with constriction of the airways (such as wheeziness and tight chest) are very poor predictors of actual narrowing. In fact diagnosing EIA based on symptoms is as effective as diagnosing with a coin toss! This has resulted in a peculiar situation where EIA is overdiagnosed in athletes who complain of symptoms and underdiagnosed in athletes who do not not complain of symptoms.

The reason for the disconnect between symptoms and airway dysfunction is not clear however there are two possible explanations. The first is that some people are just more sensitive to breathing discomfort than others and the second (which might not be entirely unrelated) is that asymptomatic athletes may in fact have symptoms but not consider them abnormal in the context of exercise. Put another way, how do you know that the effort you experience in breathing during exercise isn’t any different for that which your training partner experiences; after all everyone puffs and pants after a run!

However, obtaining a secure diagnosis is important in two respects (especially for athletes); the first relates to the health implications and the second to performance aspects. Asthma has been identified as a significant risk factor in unexplained sport-related deaths and therefore it is important to correctly treat and manage EIA in athletes. On the flip side of that, if an athlete is incorrectly diagnosed as having EIA it usually means that they are taking unnecessary medication, which in itself carries potential health risks. With regards to performance, there is evidence that untreated EIA reduces the exercise capacity in athletes an may compromise there ability to train and compete effectively.

The main cause of EIA is thought to dehydration of the airways as it tries to humidify the increased volumes of air that are breathed during exercise. The drying of the cells in the airways causes them to release signaling chemicals. These chemicals stimulate an inflammatory response (not too different from the response you get to an insect bite), which causes the smooth muscle around the airways to contract and reduce the size of the airways. The smaller airways make it more difficult to move air out of the lungs.

There is also often an allergic component to EIA especially in outdoor summer sport athletes who are exposed to large amounts of pollen during their training. The pollen enters the lungs and over time the cells in the lungs can become hypersensitive to the pollen. Once this happens, when pollen comes in contact with those cells, the cells again release those chemicals mediators that cause the cascade of events from inflammation through to bronchoconstriction. It is well established that if allergic symptoms (such as a runny or stuffy nose) are untreated they can progress to asthma. This is known as the ‘allergic march’ and highlights the importance of adopting a holistic approach in the diagnosis and management of asthma and allergies.

Dr Les Ansley is a senior lecturer in the Department of Sport and Exercise Science at Northumbria University and the Director of Sport Asthma, a consultancy that offers diagnostic testing for exercise-induced asthma.

This was posted in Bdaily's Members' News section by Jonny Marshall .