The effect of exercise on ventilatory function in the child with asthma

1. Physical exercise has two quite distinct effects on ventilatory function in the asthmatic child depending upon its duration. 2. Exercise of short duration, 1–2 minutes, produces an increase in the forced expiratory volume within 1 minute of the end of exercise. 3. Prolonged exercise, 8–12 minutes, produces a decrease in the forced expiratory volume which reaches a minimum value between 1 and 5 minutes after exercise and then rapidly increases towards the resting level. 4. The level of exercise determines the degree to which these ventilatory effects are evoked. 5. Both the increase and decrease can be minimised or abolished by preliminary broncho-dilatation with isoprenaline sulphate. This suggests that the phenomena are due to changes in the airways resistance caused by broncho-dilatation or broncho-constriction in bronchi which are already to some extent constricted.