Role of respiratory system impedance in the difference of ventilatory control between children and adults

How children are able to adapt their ventilation to the intensity of exercise faster than adults remain unclear. We hypothesized that differences of (V) over dot(E) observed between children and adults depend on either peripheral chemoreceptors or central command activity. We examined ventilatory control parameters in either normoxic or hypoxic condition (FI(O2) = 0.15). We analyzed the adaptability of the respiratory exchanges by (i) the measurement of ventilatory kinetics time-constant and (ii) the central command by the mouth-occlusion pressure (P0.1). A group of nine pre-pubescent children (mean age 9.5 +/- 1 years) and a group of eight adults (mean age 24 +/- 3.1 years) performed a constant-load exercise. In normoxia, children had significantly shorter time-constant (tau) (V)over dot(CO2) (respectively, 38.5 +/- 4.3 and 53.1 +/- 5.3 s; P < 0.001), tau (V)over dot(E) (respectively, 52.5 +/- 13.1 s vs. 66.1 +/- 12.3 s; P < 0.001),and tau P0.1 (57.4 +/- 15.4 and 61.0 +/- 12.9 s, respectively; P < 0.001) than adults. In hypoxia, children exhibited shorter tau P0.1/V(T)/T(i) compare to adults. Reinforced by the significant correlation between tau (V)over dot(E) and tau P0.1/V(T)/T(i) for children but not adults, we concluded that ventilatory response differences could be due in part to the respiratory system impedance. (C) 2008 Elsevier B.V. All rights reserved.