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Exercise-Induced Asthma

Asthma and the athlete

Most of us are likely to know someone who has exercise-induced asthma and needs a ‘puffer’ every now and then, although it usually comes as a surprise to learn just how many people are treated for asthma every day. Even more surprising is the number of athletes who overcome the symptoms of exercise induced asthma (EIA) thanks to sports medicine to perform at elite level. Unlikely as it may seem, the evidence suggests strongly that, if you are a top athlete, you are increasing your chances of developing this hazardous respiratory condition.

Asthma is the most common chronic condition in children worldwide(1). In Australia alone, two million people have clinically recognised asthma, representing around 10% of the population (2). Although Australia is reported to have a relatively high incidence of asthma, this data is on a par with the Behavioural Risk Factor Surveillance System (BRFSS) in the US, which has reported a lifetime incidence of asthma among Americans at 11.1%. Between eight and nine out of 10 asthma sufferers will experience symptoms during or after exercise(3), making this a condition that all of us involved in sports support should be aware of.

What causes asthma Asthma occurs as a result of hyper-reactivity of the airways. People with sensitive airways will be prone to recurrent episodes of coughing, wheezing, tightness of the chest and shortness of breath. These episodes arise when the lining of the airway is exposed to triggers (usually environmental, such as pollens, fungi moulds, animal allergens, tobacco smoke, etc) which prompt the immune system to release mediators that cause the airway to react and constrict. Two mechanisms contribute to this narrowing: the thin lining of the airways inflames, causing swelling and increased mucus production; and the smooth muscle that lines the airways contracts, which physically narrows the inner airway tube or lumen (this is known as bronchospasm). Among asthmatics (people with known reactive airways disease), exercise will usually be a major trigger of an episode. But ‘exercise induced asthma’, which tends to be bronchospasm rather than mucus over-production, can also occur in people with associated allergic conditions such as hayfever and eczema, and even sometimes in otherwise healthy, non-asthmatic, non-allergic individuals. This means that isolated exercise-induced bronchospasm is often undiagnosed, remaining silent and asymptomatic until the individual takes up exercise. Indeed, symptoms often occur at the completion of exercise, rather than during it. Thus exercise is estimated to trigger bronchospasm in more than 10% of the general population(4).

Asthma among athletes Thankfully there have been no reports of death linked to isolated exercise induced asthma. But the condition can still cause considerable limitations particularly in elite and professional sportspeople. Rasmussen et al found an inverse relationship between fitness levels and risk of asthma and suggested that exercise may have a beneficial effect on the control of asthma when practised at mild to moderate levels and in normal conditions(5). However, Langdeau, and Boulet(6) believed it is possible that very intense and repeated exercise, particularly when performed over many years, could cause respiratory health problems. This is based on the higher prevalence of EIA in elite athletes. Weiler et al(7) found that about 15% of athletes competing at the 1996 Summer Olympic Games reported having a previous diagnosis of asthma. The same criteria were used at the subsequent Winter Olympics in 1998 and 21% of athletes surveyed reported a history of asthma(8). Among the 2000 Australian Summer Olympic Team, 21% reported asthma or EIA(9). Kukafka et al(10) studied football players and reported that 10% had a history of treated asthma. However, among the remaining athletes, 9% had EIA based on pulmonary function testing, suggesting a large proportion of undiagnosed EIA. The number of elite athletes reporting asthma-type symptoms also appears to be increasing, although this may be the result of improved diagnostic tests.

What causes EIA? The pathogenesis of EIA is controversial. It may be the result of a change in the humidity and/or temperature of inhaled air. During aerobic exercise, people usually switch to breathing through the mouth, which means that the inhaled air bypasses the normal humidification mechanisms present in the nose. It is thought that the bronchoconstriction could be induced by water loss from the airways, heat loss from the airways, or some combination of both. This dehydration increases the concentration of airway fluid, somehow activating the inflammatory cells to cause bronchoconstriction. While the statistics suggest a link between intense exercise and EIA, this is difficult to prove. Suggestion of a definitive link would be unpopular and might well have knock-on implications for all involved in sport. Perhaps the key question is this: if such a link does exist, are the changes in respiratory function irreversible? There is very little research examining this question. Kujala et al(11) retrospectively reviewed more than 1,200 former elite athletes who had participated at least once at international level between 1920 and 1965. The prevalence of asthma among this group was not statistically different from a control group of non-athletes. This may suggest a reversal of changes associated with elite competition, but it could equally well reflect changes in training intensities, environmental factors and accuracy of diagnostic modalities over the years.

How to diagnose EIA in athletes Sports support professionals who suspect their athletes of having EIA should have them assessed by a respiratory physician and request that pulmonary function tests be performed. Asthmatics will show lower values for forced expiratory volume in one second (FEV1), compared to non-asthmatic athletes. Asthmatics will show an improved FEV1 after the use of bronchodilator medication. Non-asthmatics tend not to show statistically significant changes. Almost all elite athletes with suspected exercise-induced asthma should have some formal pulmonary testing to determine the extent of their problem. This will serve as a formal ‘challenge test’ for governing bodies as well as a pre-treatment baseline for ongoing performance evaluations. The International Olympic Committee’s Medical Commission (IOC-MC) requires objective evidence of asthma or EIA before permission is granted for the use of beta-agonist medication. The World Anti-Doping Agency (WADA) requires notification for the use of inhaled beta-agonist and corticosteroid medications. Objective evidence is required in the form of a positive direct or indirect provocation challenge test (see Table 1, above). The FEV1 is considered to be the most reliable measure of function after the tests. Therapists should regularly review current publications relevant to their athlete’s specific sport to check regulations governing their anti-asthmatic medication.

Treatment and precautions Initially, simple advice such as gradually warming up towards 80-90% of maximal intensity can decrease the severity of symptoms(12). Other non- pharmaceutical therapies such as masks and nose breathing have been shown to be effective in reducing symptoms, but are often impractical. The athlete might be encouraged to use an inhaled beta-agonist such as salbutamol within the first 15 minutes of activity, with subsequent doses of inhaled medications as necessary. If pre-activity therapy (non-pharmacological and pharmacological) is not successful in reducing symptoms, the athlete will need to try out a daily control regime of medication. Anti-asthmatics such as inhaled corticosteroids, leukotiene receptor antagonists, long acting beta-agonists, and theophyllines can be used alone or in combination. It is important to note that the use of these medications always carries a risk of side effects (albeit small). Be sure to make an ongoing evaluation of the athlete’s response to their medication regime. A number of studies of variable quality have looked at whether EIA can be relieved with dietary antioxidant supplements. Ascorbic acid (vitamin C), beta-carotene, lycopene and undenatured whey protein have all been shown to improve pulmonary function to varying degrees. Tecklenburg et al(13) found that a daily 1,500mg supplement of ascorbic acid reduced adverse changes in pulmonary function after exercise in athletes with asthma. It is hypothesised that these antioxidants protect against inflammatory damage to the airway cells, thereby reducing subsequent bronchial constriction. Bear in mind that asthma is not the only cause of breathlessness in athletes, particularly if your athlete responds poorly to anti-asthmatic medication. Other possibilities, including obstruction of the respiratory tree by a tumour, or by vocal cords that spasm during exercise; cardiovascular conditions such as septal defects (hole in the heart) and cardiac arrhythmias, should be ruled out.

Conclusion All participants in sporting activities should discuss the control of their asthma symptoms with their general practitioner or sports physician. Support professionals should try to identify specific irritants and devise a customised asthma management plan involving non-pharmaceutical and, if necessary, pharmacological interventions. The management plan should include an action plan in case of severe asthma attack. Sports that permit gradual increases in intensity and allow for variable involvement, eg team sports, are excellent for asthmatics who are keen to be active. Asthma is a serious (and potentially fatal) condition that can be distressing for the athlete and affect their performance. An understanding of a patient’s symptoms, response to therapy and ongoing evaluation are important in the continued management of this common condition.

------------------ 1. World Health Organisation (WHO) Asthma Factsheet. fs307/en/index.html (accessed: 17/08/07). 2. Australian Centre for Asthma Monitoring (2007) Asthma in Australia: Findings from the 2004-05 National Health Survey. Cat. no. ACM 10. Canberra: Australian Institute of Health and Welfare. 3. Anderson, SD (1985) ‘Exercise-induced asthma. The state of the art’. Chest 87:191S-5S. 4. Parsons, JP, Mastronarde, JG (2005) ‘Exercise induced bronchoconstriction in athletes’. Chest. Dec;128(6):3966-74. 5. Rasmussen, F, Lambrechtsen HC, et al (1999) ‘Is low physical fitness a risk factor for the development of asthma?’ [abstract]. Am J Respir Crit Care Med; 159: A416. 6. Langdeau, J and Boulet, L (2001) ‘Prevalence and mechanisms of development of asthma and airway hyperresponsiveness in athletes’ [Review Article]. Sports Medicine Volume 31(8), pp 601-616 7. Weiler, JM, Layton, T, Hunt, M (1998) ‘Asthma in United States Olympic athletes who participated in the 1996 Summer Games’. J Allergy Clin Immunol; 102: 722. 8. Weiler JM, Ryan EJ III (2000) ‘Asthma in United States Olympic athletes who participated in the 1998 Olympic Winter Games’. J Allergy Clin Immunol; 106: 267-71. 9. Corrigan, B, Kazlaukas, R (2000) ’Medication use in athletes selected for doping control at the Sydney Olympics’. Clin J Sport Med 2003; 13-40. 10. Kukafka, DS, Lang, DM, et al (1998)

Exercise-Induced Asthma