As the existence of a late reaction in exercise induced asthma is controversial, peak expiratory flow (PEF) was measured for up to 13 hours after a running test in 404 consecutive young male army conscripts undergoing assessment of their asthma. In 294 subjects (73%) the immediate post-exercise fall in PEF was 10% or more; the mean (SD) fall in PEF in this group was 27% (15%). Nine patients with exercise induced asthma had a fall in PEF of 20% or more 4-13 hours after the exercise test. In these possible "late responders," however, the change in PEF 4-13 hours after exercise was similar to the change in PEF on control days before and after the exercise day, and the lowest PEF during this period was similar to the lowest measurements on the control days. These nine subjects showed pre-exercise bronchodilatation. Their pre-exercise PEF, from which the percentage fall in PEF was calculated, was 24% (9%) higher than the mean PEF level on control days. This study supports the view that what appears to be a "late asthmatic reaction" after exercise is an artefact. Spontaneous within day fluctuation in pulmonary function, pre-exercise bronchodilatation, and the fact that airflow obstruction persists after the early postexercise response may give a false impression of an exercise induced late asthmatic response in patients with labile airways.
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