ABSTRACT. The purpose of this study was t o determine how ventilation (VE) and C 0 2 production (VC03 in response to exercise change during the growth process in children and teenagers. Dynamic gas exchange responses were measured in two types of studies: 1) 128 healthy children ranging in age from 6 to 18 yr performed progressive exercise tests ("ramp" type protocol) for measurement of,the slope of the relationship between VE and VCOZ-AVE/AVCOZ; and 2) the response characteristics of VE and VC02 in the transition between rest and exercise were measured in 11 teenagers and 11 younger children. Gas exchange was measured breath by breath. We found a small but significant decrease in AVE/AVCOz with increasing body weight ( r = -0.46, p <0.05), height, or age (mean slope of 27 in the youngest in 21 in the .oldest subjects). The response characteristics of VE and VCOZ (measured as the time constant of the best-fit exponential response) were longer than for VOz in both younger children and teenagers; but the time constants for VE and VC02 were each approximately 30% faster in younger children compared to teenagers. In addition, end-tidal PCO, during exercise was significantly lower in the younger subjects (mean value of 39.6 torr) compared to the teenagers (mean value of 43.5 torr). The results suggest that the process of respiratory control in exercise matures to a small degree during childhood in that PCO, may be regulated at lower levels in younger children and there may be growth-related differences in the relative amounts of COz that can be stored in tissues. (Pediatr Res 21: 568-572, 1987) Abbreviations vE, ventilation VC02, COZ output V O~, O2 uptake AT, anaerobic threshold RCP, respiratory compensation point Babies have different respiratory control than do adults. For example, the arterial PC02 is regulated at lower levels, the pattern of breathing is erratic and marked by periodicity, and the ventilatory response to hypoxia and hyperoxia differs from the adult (1, 2). Thus, while it is apparent that the respiratory control apparatus undergoes maturation in the normal human being, there is a dearth of information on the ontogeny of these mechanisms during childhood. We hypothesized, therefore, that maturation of respiratory control could be detected and characterized during growth in children.In adults, it is known that the degree of V, is linked to the metabolic production of C 0 2 (3-8). This linkage is marked by homeostasis for C 0 2 concentration in the blood, such that PC02 is kept within a very narrow range despite large fluctuations in the VC02 as occur during exercise. But the child is faced with problems not encountered by the mature individual-while the ventilatory apparatus in both the adult and child must quickly respond to the increased C 0 2 load induced by physical activity, the child must, in addition, deal with greater C02 loads imposed by the increasing body size of the growth process itself. This research is focused on the precise linkage between VC02 and VE during exercise in growing ch...