Exercise induced asthma

# Overview
Exercise-induced asthma, or E.I.A., is a medical condition characterized by shortness of breath induced by sustained aerobic exercise. In patients with bronchial hyperresponsiveness, vigorous physical activity triggers acute narrowing of the airways and is measured by the number of sputum eosinophils. E.I.A. shares many features with other types of asthma, and responds to some typical asthmatic medications, but does not appear to be caused by the same inflammatory reaction as the other types.

# Pathophysiology

## Triggering Factors
- Exposure to cold or dry air 
- Bronchial hyperresponsiveness
- Increased duration and intensity of exercise
- Concomitant viral infection
- Environmental allergen

## Pathogenesis
- The underlying pathogenesis for E.I.A. is poorly understood.
- E.I.A usually occurs after at least several minutes of vigorous, aerobic activity, which demands supplementation of normal nasal breathing with mouth breathing. The resultant inhalation of air is neither warmed to bod temperature or humidified by the nasal passages; hence, seems to generate increased blood flow to the linings of the bronchial tree, resulting in edema and subsequent constriction of these bronchial vessels, worsening the degree of obstruction to airflow. This sequence generates symptoms similar to those seen in other forms of asthma, but occurs without the inflammatory changes that underlie them.

# Epidemiology and Demographics
The prevalence of E.I.A in the general population is approximately 7-20%. The majority of asthmatics with symptomatic disease have some degree of exercise induced asthma.

# Diagnosis

## History and Symptoms
- Initial bronchodilation occurs 6-8 minutes after exercise with subsequent bronchospasm and completely resolves within an hour. During this approximate one hour period, resumption of exercise will likely produce either none or mild symptoms.
- In most cases, a relative refractory period follows resolution of an attack and is thought to be secondary to the release of inhibitory prostaglandins such as prostaglandin E2.
- Most often than not, approximately 6-10 hours after an initial attack, a rebound attack with milder symptoms often develops without precipitating exertion.
- Severe attacks are often the result of someone with both, allergic and exercise-induced asthma exercising in a high-allergen environment (e.g. walking uphill alongside slowly moving traffic at dusk) and can be fatal.
- Common symptoms include:
- Shortness of breath
- Cough
- Wheeze
- Altered metal status may be the presentation in severe attacks

## Physical Examination

### Vital Signs
- Tachypnea
- Tachycardia

### HEENT
Cyanosis secondary to severe hypoxia

### Lungs
High-pitch prolong expiratory wheeze that may be audible even without a stethoscope.

## Other Diagnostic Studies

### Exercise Challenge Test
- Exercise challenge test is a direct method to establish diagnosis. Test is considered positive if a 10% reduction in FEV1 is observed after a 6-8min treadmill exercise.
- In athletes, documentation of airway narrowing in response to exercise, aids in the diagnosis and management of asthma by providing evidence of bronchial hyperresponsiveness that will respond to treatment with inhaled corticosteroids and is usually associated with a reduction in respiratory symptoms on exercise.

# Treatment

## Medical Therapy
- The major goal of therapy in exercise-induced asthma is to ensure exercise is not avoided.
- In athletes who wish to continue their sport, and/or do so at times in adverse conditions, preventive measures, including altered training techniques and medications, can be taken.
- Some athletes take advantage of the refractory period by precipitating an attack by "warming up" and then timing their competition such that it occurs during the refractory period. Step-wise training works in a similar fashion. An athlete warms up in stages of increasing intensity, using the refractory period generated by each stage to get up to a full workload.
- Therapy should be routinely monitored with the assessment of peak expiratory flow rate performed before and after the exercise. Methacholine challenge test is another alternative to objectively assess response to therapy.
- Fish oil supplementation may represent a potentially beneficial non-pharmacologic intervention for patients with exercise-induced asthma.
- The most common medication approach is to use a beta agonist about twenty minutes before exercise.
- Equipotent doses of the bronchodilators such as salmeterol, formoterol and terbutaline have shown to be effective with respect to their short-term protective potency against exercise-induced bronchoconstriction.
- Tachyphylaxis developed to the protective effect of long and short-acting beta-2 agonist and hence is less effective when used for exercise-induced asthma. However, it remains extremely effective in the prevention of bronchospasm when used immediately before exercise.
- Nedocromil and cromolyn administered by a pressurized aerosol has shown to provide equal protection against exercise-induced asthma in children. A small randomized study, has shown the additive effects of combining cromolyn and beta-2 agonist and may be indicated in high-performance athletes. Nedocromil sodium used before exercise has shown to reduce the severity and duration of exercise-induced bronchoconstriction.
- Inhaled corticosteroids used for weeks and months before exercise significantly attenuated exercise-induced bronchoconstriction; however, it does not provide any short-term benefit.
- Montelukast has shown to provide significant protection against exercise-induced asthma and further reduce the urinary excretion of leukotriene that is commonly observed after exercise. However, leukotriene inhibitors are not effective in all patients with exercise induced asthma.
- Other pharmacological agents that have been hypothesized to provide therapeutic benefits in patients with exercise induced asthma include frusemide, prostaglandin-E2, indomethacin, and heparin.
- As evidenced by the many professional athletes who have overcome E.I.A. using some combination of the above treatments, the prognosis is usually very good.
- Olympic swimmers Tom Dolan, Amy Van Dyken, and Nancy Hogshead, baseball Hall of Famer Catfish Hunter, and American football player Jerome Bettis are among the many who have done so.
- At the same time, it should be noted that according to International Olympic Committee statistics, during most of Olympic Games in last 20 years from 1/3 to 2/3 of athletes claimed to have asthma.
- Some medical experts tie such inordinate rates of reported asthma with athletes' desire to use complex medication to help them achieve better results.

## Future or Investigational Therapies
- A randomized crossover study compared oral montelukast with inhaled salmeterol, both given two hours before exercise. Both drugs had similar benefit but montelukast lasted 24 hours.
- In a large randomized study in children, monotherapy with montelukast and combination therapy with montelukast and budesonide yielded higher beneficial results in comparison to budesonide monotherapy and combined therapy with budesonide and formoterol.