Exercise Induced Bronchoconstriction: Diagnosis

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On the surface, making a diagnosis of exercise-induced bronchoconstriction (EIB) should not to be too hard. After all, having an asthma attack while exercising would make the diagnosis fairly apparent.  However, as I mentioned earlier, self reported symptoms associated with exercise such as shortness of breath and chest tightness can be associated with a number of causes, both respiratory and non-respiratory, including just being out of shape.   In fact, in one study, approximately half of elite athletes with symptoms suggestive of EIB were found to have normal lung function.  Even more interesting is the fact that nearly half of the athletes who did not feel that they had EIB in fact tested positive for it.

Because symptoms alone are not sufficient, an objective test is required to make an accurate diagnosis.  The best tests for EIB either directly measure airway changes during exercise or produce the inflammatory changes in the airways that occur in patients with EIB and therefore serve as a surrogate for an exercise challenge.

An exercise challenge starts with a baseline pulmonary function determination with serial lung function measurements taken following a period of prescribed exercise.   A typical protocol might include running on a treadmill for 6-8 min at 80-95% of an athlete’s calculated max heart rate.  This level of exercise requires significant effort but is required to produce changes associated with EIB in highly trained athletes.  Following the effort, lung function values are recorded at 5, 10, 15, and 30 minutes and compared with the pre-challenge numbers.  A 10% or greater drop in lung function persisting for at least 15 minutes after exercise has stopped is diagnostic of EIB.

Because EIB is triggered in some athletes by inhalation of cold, dry air, a weakness of an exercise challenge on an indoor treadmill is indoor humidity that may be significantly different form the sport environment.  For this reason, sport and environment specific challenges (field challenges) have been found to be more sensitive than tests run in controlled indoor environments.  This is particularly true for those involved in winter sports such as ice skating and skiing and may very well be important for athletes who train in a desert environment such as Phoenix.   In some, the level of intense exertion present in competition may not be reproduced exercising in a calm, indoor setting, producing falsely negative results.

Several alternatives to an exercise challenge have been developed including what is called Eucapnic Voluntary Hyperpnoea or EVH.  In this test an athlete breathes a specially formulated, dry, gas mixture at a rapid rate to replicate the conditions of a hard exercise cession.  This is currently the only test recommended by the International Olympic Commission to identify EIB in Olympic athletes.  Unfortunately, the test requires specialized equipment and is not without some risk of precipitating a severe asthma attack.  For this reason the test is not widely available, in spite of the IOC recommendations.

Although an objective diagnostic test for EIB is recommended when possible, another approach to is to treat the athlete with an asthma regimen and see if symptoms improve. I’ll discuss more about this in the next post when I review treatment of EIB.

Exercise Induced Bronchoconstriction: What, When, and Where

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Exercise-induced bronchoconstriction or bronchospasm (EIB) is defined as acute airway narrowing occurring as a result of exercise.  In the previous post I discussed that exercise, particularly vigorous, aerobic exercise, frequently triggers symptoms in patients who have a diagnosis of asthma but can also cause asthma symptoms, wheezing, shortness of breath, cough, and chest tightness, in athletes who have never had asthma.

Feeling very short of breath after a hard aerobic workout does not mean that you have asthma.  More often it means you are a bit out of shape.  So how can we tell the difference between symptoms caused by going too hard and symptoms caused by EIB?

One difference is that symptoms of EIB do not track with heart rate.  Getting out of breath because of de-conditioning or exercising beyond your aerobic capacity occurs when you are not able to deliver enough oxygen to your muscles to meet their demand.   Your heart beats rapidly and you breath faster and deeper to try to deliver more oxygen to meet the demand. But once you reach your limit, oxygen-starved muscles cannot keep going and you have to slow down or stop.  When you do, your heart rate and breathing slows and the shortness of breath and sensation of air hunger quickly improves.

With EIB however, symptoms do not usually begin until well into an exercise cession, and most importantly, will continue for 30 to 60 minutes after exercising has stopped.

In fact, it is believed that rapid breathing during exercise has a cooling and drying effect on the lining of the airways, which in patients with EIB triggers inflammation.  This inflammation is similar to an allergic asthma attack and will continue after exercising has stopped.  Because cooling and drying of the airways triggers inflammation, symptoms of EIB are more likely to occur during periods of exercise out of doors when the air is cold and dry.   Other environmental conditions that have been found to contribute to EIB include high ozone and particulate levels in the air.

Cold, dry air with high ozone and particulate levels describe conditions frequently encountered in Phoenix and other desert communities in the fall and winter. Athletes involved in aerobic sports requiring high respiratory volumes over an extended period of time such as runners and cyclists are most vulnerable. In fact, exercise induced bronchoconstriction occurs in up to 15% of distance runners.

I will review diagnosis and treatment options for EIB in future posts.