Asthmatic children, known to be susceptible to exercise-induced bronchoconstriction, exercised by running or walking on a treadmill. Changes in airways obstruction were estimated by measurement of peak expiratory flow rate before, during, and after exercise. Post exercise bronchoconstriction reached a maximum when the duration of exercise was 6 to 8 minutes and when the gradient of the treadmill was 10 to 15%; exercise for longer periods or at steeper gradients produced no significant increase in bronchoconstriction. Bronchoconstriction was much greater after running than after walking at the same oxygen consumption in 4 out of the 5 subjects tested.
The reproducibility of bronchoconstriction was good in individual patients when tests performed within one day or within one week were compared. Reproducibility diminished as the interval between tests increased to one month or one year. When tests were repeated at 2-hourly intervals throughout the day, no significant diminution in exercise-induced bronchoconstriction was noted. Variations in pre-exercise peak expiratory flow rate had no significant effect on exercise-induced bronchoconstriction in individual subjects.
The range of response of normal children to treadmill exercise is defined and the value of the test in discriminating between asthmatic and other children is shown.
If several tests are to be carried out by an individual patient, they should be performed on separate days at the same time of day and should be completed within one week. This will allow accurate comparisons to be made between tests in, for example, the assessment of the effect of different drugs in an individual patient.
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