Ventilatory response of prepubertal boys and adults to carbon dioxide at rest and during exercise

The aim of this study was to determine whether the greater ventilation in children at rest and during exercise is related to a greater CO2 ventilatory response. The CO2 ventilatory response was measured in nine prepubertal boys [10.3 years (SD 0.1)] and in 10 adults [24.9 years (SD 0.8)] at rest and during moderate exercise (VCO2 = 20 ml.kg-1.min-1) using the CO2-rebreathing method. Three criteria were measured in all subjects to assess the ventilatory response to CO2: the CO2 sensitivity threshold (Th), which was defined as the value of end tidal PCO2 (PETCO2) where the ventilation increased above its steady-state level; the reactivity slope expressed per unit of body mass (SBM), which was the slope of the linear relation between minute ventilation (VE) and PETCO2 above Th; and the slope of the relationship between the quotient of tidal volume (VT) and inspiration time (tI) and PETCO2 (VT.tI-1.PETCO2(-1)) values above Th. The VE, VT, breathing frequency (fR), oxygen uptake (VO2), and CO2 production (VCO2) were also measured before the CO2-rebreathing test. The following results were obtained. First, children had greater ventilation per unit body weight than adults at rest (P < 0.001) and during exercise (P < 0.01). Second, at rest, only VT.tI-1.PETCO2(-1) was greater in children than in adults (P < 0.001). Third, during exercise, children had a higher SBM (P < 0.02) and VT.tI-1.PETCO2(-1) (P < 0.001) while Th was lower (P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)