Ventilatory Control during Exercise in Normal Children

We investigated the relation between age and respiratory control during exercise in 80 children aged 6.4-17.6 y (42 male, age, 11.6 ± 3.3 y; body weight, 41.3 ± 14.7 kg; and 38 female, age, 12.6 ± 2.7 y; body weight, 42.5 ± 9.3 kg). Exercise tests were performed on a treadmill after a standard symptom-limited Bruce protocol. Data were analyzed separately for boys and girls. At rest and at peak exercise, the ratio of minute ventilation to carbon dioxide production(˙VE/˙VCO2), the ratio of effective alveolar ventilation to carbon dioxide production(˙VA/˙VCO2), the ratio of pulmonary dead space to tidal volume (Vd/V t), and arterial PCO2 (PaCO2) were not correlated with age. At the exercise intensity of ventilatory anaerobic threshold, the PaCO2 increased, and the ˙VA/˙VCO2 decreased, significantly with age, whereas the Vd/V t was not related to age. Linear regression analysis demonstrated that the slope of the relationship between ˙VE and ˙VCO2(Δ˙VE/Δ˙VCO2) and the slope of the relationship between ˙VA and ˙VCO2(Δ˙VA/Δ˙VCO2) decreased with age. There were no gender differences in the regression slopes and the intercepts of the relationships. Results show that younger children breathe more during exercise to eliminate a given amount of CO2 to keep PaCO2 set point slightly but significantly lower than older children. This age dependence must be considered in investigating ventilatory control during exercise in children.