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Quite often, it is difficult to clinically tease-out breathlessness secondary to asthma, and breathlessness secondary to alternative diagnoses.
Most patients with asthma are given the advice to take their short-acting inhaler, eg, salbutamol, pre-exercise and then also use it on development of symptoms. However, the main side-effects of salbutamol include tachycardia, palpitations, tremor and anxiety, which in turn can lead to hyperventilation. These symptoms can aggravate or perpetuate breathlessness.
Furthermore, excessive salbutamol usage, or salbutamol without regular inhaled steroids, can down-regulate receptors, making the user unresponsive to the drug, a phenomenon known as tachyphylaxis.
There are a few key messages about exercise-induced asthma, or to use the correct term, exercise-induced bronchoconstriction (EIB). Firstly, asthma generally causes breathlessness when spirometry is impaired before exercise.
Secondly, symptoms typically occur approximately 10-to-15 minutes or so after exercise and are less likely during. Symptoms also usually resolve over 30-to-60 minutes.
Thirdly, the predominant symptoms tend to be cough, wheeze and chest tightness, rather than breathlessness.
EIB is an acute narrowing of the airway that occurs as a result of exercise. Exercise is a common trigger of bronchoconstriction in patients with asthma. Many patients with asthma suffer exercise-induced respiratory symptoms. It is important to note that EIB can also occur in non-asthmatics, with a prevalence of approximately 20 per cent.
EIB may occur as a consequence of alterations in airway physiology caused by the inhalation of a large volume of cool, dry air while exercising. The effect of large-volume dry air inhalation on the airway surface osmolality may be the main trigger for bronchoconstriction.
The full sequence of events that trigger EIB are not clear as of yet. However, it is believed that the release of inflammatory mediators, such as histamine, tryptase and leukotrienes, are involved.
In addition, sensory nerve stimulation is thought to be associated with a release of mucus into the airways after a period of exercise.
The differential diagnosis of breathlessness on exertion depends on the age and sometimes gender of the patient.
It includes the following: EIB; exercise-induced laryngeal obstruction (EILO); normal physiologic exercise limitation; hyperventilation; central airway obstruction; laryngotracheomalacia; parenchymal pulmonary disease; gastro-oesophageal reflux; coronary heart disease; and heart failure.
Some of these diagnoses may be suspected at initial interview and examination but spirometry, electrocardiography and chest radiology can be very helpful.
Ultimately, the test of choice for the diagnosis of EIB is exercise spirometry.
In the above case, the patient primarily reported throat symptoms during exercise, which suggests the most likely diagnosis was EILO.
EILO is a condition that is associated with the vocal cords and supraglottic structures in the larynx where the flow of air may become obstructed during exercise.
A series of lung function measurements after exercise or a hyperpnoea challenge are used to assess whether EIB is present. They are also used to evaluate the extent of the disorder.
It is advisable to examine FEV1, as this measurement is easier to repeat than others. FEV1 has been found to be more sensitive than the peak expiratory flow rate. Symptoms usually resolve spontaneously and the FEV1 should return to 95 per cent baseline value within 30-to-90 minutes.
The percentage fall in FEV1 from the baseline value is used to denote the response of the airway. The difference between the pre-exercise FEV1 value and the lowest FEV1 value recorded in 30 minutes post-exercise is expressed as a percentage of the pre-exercise value. A fall of ≥10 per cent in FEV1 is the benchmark for a diagnosis of EIB.
The percentage fall in FEV1 from pre-exercise can then be used to grade the severity of EIB. It is classed as mild (≥10 per cent but <25 per cent); moderate (≥25 per cent but <50 per cent); or severe (≥50 per cent).
However, a decline in FEV1 of ≥30 per cent in those on inhaled corticosteroids would be considered severe.
The American Thoracic Society (ATS) released guidelines in 2012, which outlined the treatment regimen for EIB.
For patients with EIB, the administration of an inhaled, short-acting B2 agonist (SABA) before exercise is recommended. The SABA should be used 15 minutes before exercise.
As discussed earlier, it is important to remember that the repeated use of SABAs can lead to a tachyphylaxis. Therefore, if patients are using the SABA daily or more frequently, they may need an additional therapy to be initiated.
This is also true for those individuals who continue to have symptoms while using a SABA. In these cases, the next step involves the daily use of an inhaled corticosteroid (ICS). It is important to notify the patient that it may take two-to-four weeks to see maximal improvement with the ICS.
A leukotriene receptor antagonist may provide additional protection for EIB. The decision to choose between an ICS and a leukotriene receptor antagonist is made on an individual basis, taking patient preference and lung function into account. The use of a mast cell stabilising agent and inhaled anticholinergic agents prior to exercise may play a supporting role.
An antihistamine may provide added symptom relief in those with allergies and EIB who have already been commenced on a SABA. Specific warm-up routines prior to exercise and strategies to pre-warm and humidify air during exercise (eg, mask/scarf) are also used in controlling symptoms in EIB.
EIB, although quite prevalent, is often over-diagnosed and confused with more benign disorders. Diagnosis is confirmed by exercise spirometry.
Treatment is difficult because the main treatment, SABAs, demonstrate tachyphylaxis when overused.
A 12-year-old boy was referred by his GP for evaluation of possible exercise-induced asthma. The boy was generally fit and active and was a keen sports player. He described the development of a lump or discomfort in his throat whenever he performed vigorous exercise and this forced him to stop running. He denied any cough or wheeze. He used a salbutamol inhaler before any sport. His mother stated that she never noticed any cough or wheeze but had noticed him stopping for breath in the middle of a match on a number of occasions.
He was given a clinical diagnosis of asthma at age 5. There was no family history of atopy. He had never smoked and didn’t recall any excessive exposure to dusts, fumes, or moulds. His medications included a salbutamol inhaler, which he used most days pre-exercise, and a Beclazone (steroid) inhaler, two puffs twice-daily, which he felt had helped since it was started, a month before his presentation.
On examination, his resting oxygen saturations were 98 per cent. He had good air entry bilaterally, with no added wheeze or crackles. The rest of the exam was unremarkable. Resting spirometry was normal. He was advised to stop all inhalers and he was then sent for exercise spirometry testing. Figure 1 shows the exercise spirometry in this case.
There was no reduction in the forced expiratory volume in one second following exercise.
On follow-up review, his symptoms had resolved spontaneously.
Fig 1: Exercise spirometry testing
(complete list of references available on request)
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- Boulet LP, et al. Asthma and exercise-induced bronchoconstriction in athletes. New England Journal of Medicine 2015; 372:641-8.DOI: 10.1056/NEJMra1407552.