Exercise Induced Asthma

Transient narrowing of the airways that begins during or, more typically, 5 to 15 minutes after vigorous exercise, and peaks at 5 to 15 minutes after stopping before settling in 30 to 60 minutes. The term exercise induced bronchoconstriction covers people with and without chronic asthma. It is diagnosed by a fall in forced expiratory volume in 1 second (FEV1) of 10% or more from baseline.

• It affects about 80 to 90% of people with asthma and about 5 to 20% of the general population, and up to about 30 to 50% of elite winter athletes and swimmers.
• Mechanism: loss of heat and water from the airways during hyperventilation of dry air raises osmolarity of the airway surface, causing mediator release (histamine, leukotrienes, prostaglandins) from mast cells and eosinophils and airway smooth muscle contraction. Cold air, pollutants, chlorine and pollen worsen it. A refractory period of 1 to 4 hours follows an attack.
• Symptoms with exercise in a person with asthma often mean that asthma is poorly controlled.

• Cough, wheeze, chest tightness, breathlessness, excess mucus or throat irritation that begins during or after exercise, and fatigue out of proportion to effort. Performance is limited by symptoms. Some athletes have cough only.
• Examination between episodes is normal.
• Differential diagnosis: inducible laryngeal obstruction (stridor on inspiration at peak exercise, resolves in minutes), deconditioning, obesity, cardiac causes (arrhythmia, hypertrophic cardiomyopathy, coronary anomaly), dysfunctional breathing and hyperventilation, anaemia, gastro oesophageal reflux, pulmonary hypertension, interstitial lung disease, and vocal cord dysfunction.
• Complications: poorly controlled asthma, avoidance of exercise and loss of fitness, rare severe attacks and, with concurrent poorly controlled asthma, life threatening events.

• Clinical history, plus objective testing in athletes and when treatment fails:
  • Spirometry at rest, and review of response to a short acting bronchodilator (rise of 12% and 200 mL or more).
  • Exercise challenge on a treadmill or cycle ergometer: 6 to 8 minutes at 80 to 90% of maximum heart rate with dry air inspired; measure FEV1 at 5, 10, 15, 20 and 30 minutes after exercise; a fall of 10% or more on two consecutive time points supports the diagnosis (15% or more in an unselected population).
  • Eucapnic voluntary hyperpnoea (breathing dry air with 5% carbon dioxide at a target ventilation of 85% of the predicted maximum for 6 minutes): a fall in FEV1 of 10% or more is positive, and this is the preferred test for elite athletes.
  • Mannitol challenge (incremental doses to 635 mg): positive with a 15% fall at a cumulative dose of 635 mg or less, or a 10% fall between consecutive doses; methacholine challenge for baseline airway hyperresponsiveness (PC20 less than 8 mg/mL).
  • Exhaled nitric oxide greater than 25 ppb suggests eosinophilic inflammation.
• Laryngoscopy during exercise if inducible laryngeal obstruction is suspected. ECG and echocardiography when cardiac causes are possible.

• Non-drug measures: warm up for 10 to 15 minutes with intervals of high intensity effort followed by rest (induces a refractory period), breathe through the nose, wear a face mask or scarf in cold conditions, avoid exercise in cold, dry or polluted air and during high pollen counts, and avoid chlorinated indoor pools if symptoms follow.
• Pre-exercise treatment:
  • Salbutamol 200 to 400 micrograms (2 to 4 puffs) by spacer 10 to 15 minutes before exercise; protection lasts about 2 to 4 hours (children 100 to 200 micrograms). Regular daily use causes tolerance, so use only before exercise.
  • Budesonide formoterol 160/4.5 micrograms, 1 puff before exercise (formoterol acts within 5 minutes and lasts 12 hours) for patients already using maintenance and reliever therapy.
  • Ipratropium 40 to 80 micrograms (2 to 4 puffs) before exercise is less effective but may add benefit.
  • Sodium cromoglicate 10 mg (2 puffs) or nedocromil 4 mg 15 to 20 minutes before exercise is an alternative (short acting, evidence is limited).
• Daily controller therapy (when symptoms occur with exercise more than twice a week, or when asthma is uncontrolled):
  • Inhaled corticosteroid, for example budesonide 200 to 400 micrograms twice daily or beclometasone 100 to 200 micrograms twice daily, taken for 4 to 6 weeks and then reviewed; this reduces the severity and frequency of exercise symptoms.
  • Montelukast 10 mg once daily (5 mg for ages 6 to 14, 4 mg for ages 2 to 5); effective in about half of patients and acts within 2 hours, with a persistent effect without tolerance; monitor for neuropsychiatric effects.
  • Combined inhaled corticosteroid and long acting beta agonist (budesonide formoterol 160/4.5, 1 to 2 puffs twice daily) for moderate persistent asthma; do not use a long acting beta agonist alone.
  • Leukotriene antagonist plus antihistamine for coexisting allergic rhinitis, and intranasal fluticasone 2 sprays each nostril daily.
• Review technique and adherence, and check for gastro oesophageal reflux, obesity, and untreated rhinitis.
• Athletes: check which inhaled agents and doses are permitted by the anti-doping rules for the competition before use; document the diagnosis with objective testing.
• Management of an attack: stop exercise, sit upright, salbutamol 4 to 10 puffs by spacer every 20 minutes up to 3 doses; seek urgent help if there is no improvement within 20 minutes, or if breathing is severe.
• Special groups:
  • Children: salbutamol 100 to 200 micrograms by spacer before play; montelukast 4 to 5 mg; encourage regular physical activity.
  • Pregnancy: salbutamol and inhaled corticosteroid are safe; maintain exercise at moderate intensity.
  • Elderly or cardiac disease: exclude cardiac causes of exercise symptoms before attributing them to asthma.
• Red flags: exercise related chest pain, syncope, palpitations, stridor (consider inducible laryngeal obstruction), symptoms at rest, poor response to treatment.
• Follow up: review at 4 to 6 weeks after starting treatment, repeat challenge testing if symptoms persist, and yearly review of control and technique.