Exercise Induced Bronchoconstriction: What, When, and Where

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.