People with exercise induced asthma often have perfectly normal respiration at rest, and therefore have to exercise to provoke a reaction which will prove their condition.Hence the following.No 3 in particular.
Testing for EIA
With the above mechanistic basis in mind, there are three recommended methods of ‘challenging’ the airways in order to test for EIA. These are as follows:
1. Eucapnic voluntary hyperventilation
challenge(2): This test involves breathing dry air at a level of breathing that is equivalent to 30 times the athlete’s FEV1 for at least six minutes. This test simulates the dehydrating effect that high levels of breathing during exercise exert on the airways, and is therefore highly specific to EIA. Lung function is measured at discrete time intervals for up to 30 minutes after cessation of hyperventilation. A positive diagnosis is made with a fall in FEV1 greater than 10% from baseline at two or more time points post-challenge.
2. Mannitol challenge (3): Mannitol is a harmless sugar that is inhaled progressively increasing doses to induce airway dehydration. Dehydration occurs because the sugar particles that are deposited in the airways draw moisture from the airway lining cells, dehydrating them in a similar way to exercise. Mannitol therefore triggers EIA in a very similar way to exercise, but without all the ‘puffing and panting’. In this respect a mannitol challenge is also a very specific test of EIA. Lung function is measured after each dose, and compared to the baseline value. A positive diagnosis is made with a fall in FEV1 greater than 15% from baseline at any inhaled dose or a 10% incremental fall in FEV1 between doses.
3. Exercise challenge: This is the most specific test of EIA and normally consists of a single bout of exercise lasting a minimum of six minutes at an intensity equivalent to 80-90% of maximal heart rate. However, this can be the least reliable challenge, since its outcome is highly dependent upon environmental conditions. Because the trigger for EIA is airway dehydration, the response to an exercise challenge is highly dependent upon the magnitude of ventilatory response achieved during the challenge bout of exercise, as well as the water content of the inhaled air. If the test is undertaken in, say, an air conditioned laboratory, airway dehydration may be insufficient to trigger EIA. However, an exercise challenge that is conducted in the athletes’ competitive environment, eg, snow clad mountains, may provide the only setting in which EIA is triggered. A positive diagnosis is made with a fall in FEV1 greater than 10% from baseline at two or more time points post-exercise.
Selection of the test will be ‘situation specific’, and dependent upon the facilities that are available to the athlete and physician.