Effect of Disodium Cromoglycate on Ventilation and Gas Exchange During Exercise in Asthmatic Children With a Postexertion FEVi Fall Less Than 15 Percent: Comment
In the aforementioned situations, the ratio of physiologic dead space to tidal volume (Vt) fails to decrease normally or tends to increase during the exercise, and thus the regional unevenness of ven-tilation-perfusion ratios can result in a higher Ve for the work rate performed We have found that in test A, a greater Vt accounted for the higher ventilatory requirement at comparable work loads, whereas respiratory rates were unchanged. A similar change in Ve and Vt, along with a higher ratio of physiologic dead space to Vt, has been described during exercise in asthmatic children with respect to normal subjects.
On account of the variability in aerobic power and working capacity reported in asthmatic subjects, as compared with normal individuals,’ we previously emphasized the usefulness of the EC of running, ie, the energy required above resting to transport the subject’s body per unit distance, as an index of the efficiency of energy utilization. In the present study, we found a significantly lower EC of running when asthmatic subjects were pretreated with DSCG, with reduced levels of V02 and Ve at comparable work loads. Hyperventilation present at any level of exercise is thought to increase the cost of breathing in asthmatic patients. Casan and coworkers showed that, incrementing added dead space, V02 increases more than with an added resistance, demonstrating that changes in physiologic lung volumes may influence the oxygen cost of breathing and the overall energy expenditure of the body. We speculate that in untreated subjects the higher EC of running is related to the higher ventilatory request. inhalers for asthma
Up to date, several mechanisms of action have been proposed for DSCG in the prevention of EIA, but to our knowledge, no data are available about a possible effect of the drug on the ventilation and gas exchange in exercising asthmatic subjects. Only Terada et al described a possible effect of cromolyn sodium on gas exchange, showing a reduced CO2 accumulation in dogs undergoing high-frequency ventilation. Recently McFadden postulated that DSCG could modulate the response of the airway microvasculature to exercise. In our case, this looks like an intriguing hypothesis that could account for an action of the drug on small airways.
In conclusion, we found that DSCG is effective in reducing the ventilatory demand and the EC of running during a maximal treadmill exercise also in asthmatic children who present a postexertion FEVi reduction lower than 15 percent from the baseline. The greater ventilatory requirement occurring during the run in asthmatic children without premedication seems not to be related to the degree of airflow limitation, measured by a standard spirometric parameter such as FEVi, at the end of exertion. This finding suggests that, even in the presence of a mild degree of postchallenge airway obstruction, asymptomatic asthmatics could present slight abnormalities of gas exchange during exercise.