Maturation of Ventilatory Responses to 1-Minute Exercise

Abstract

ABSTRACT. To test the hypothesis that ventilatory responses to exercise mature during growth in healthy children, we examined C 0 2 production (VCO~) and minute ventilation (VE) before, during, and for 10 min after 1-min bursts of cycle ergometry exercise. Ten children (range: 7-11 y old) and 13 adults (26-42 y old) exercised at work rates corresponding to 50 and 80% of the anaerobic or lactate threshold, 50% of the difference between anaerobic threshold and maximum 0 2 consumption, 100% of maximum O2 consumption, and 125% of maximum 0 2 consumption (125% max). Gas exchange was measured breath by breath. Children recovered faster from high-intensity (above anaerobic threshold) exercise as judged by the time constant of single exponential curve-fits to postexercise Vco2 (55 f 10 s (1 SD) at 125%. max in children compared with 92 2 17 s at 125% max in adults; p < 0.0011 and VE (58 f 10 s at 125% max in children compared with 125 & 37 s in adults, p c 0:001). Although we found no significant difference between VCOZ and VE recovery times in children, VE was significantly slower than Vco2 in adults for highintensity exercise. Moreover, recovery times in adults increased with work intensity but were independent of them in children. Whereas the C 0 2 costs [calculated as total C 0 2 produced above baseline per unit work done (mL. J-I)] increased with work intensity in adults, no similar significant relationship was observed in children. Finally, at 125% max, the ratio of C 0 2 cost to O2 cost was 1.48 f 0.07, less than the ratio in adults (1.83 -C 0.07, p < 0.01).These results demonstrate marked differences in dynamic ventilatory response to short bursts of exercise reflecting maturation of both respiratory control and cellular metabolic factors. (Pediatr Res 29: 362-368, 1991) Abbreviations AT, anaerobic threshold VCOZ, C 0 2 production VE, minute ventilation VO~, 0 2 consumption Petco2, end-tidal Pco2 Vo2max, maximum O2. uptake A, difference between V02max and AT % max, % of Vo2max 7Vco2, time constant for V C O~ recovery 7VE, time constant for Ve recovery Ventilation in humans is regulated to maintain cellular homeostasis of COz and bicarbonate when the metabolic rate changes. The link between cellular activity and ventilation is, in large part, dependent on the distribution and transport of .COz molecules (l,2). There is evidence that the linkage between Vco2 and VE undergoes a process of maturation during growth, i.e. there is a difference between children and adults in the ventilatory response to changes in metabolic rate (3). The magnitude and mechanisms of these differences have not been fully elucidated, most likely because studying gas exchange in ways that are acceptable to children is difficult and because there are no uniform approaches to normalizing physiologic responses in subjects of widely different sizes. In this study, we employed an exercise protocol specifically designed for the behavioral characteristics of children, and the data were normalized and analyzed in a manner that facilitated compar...

Breath-to-breath “noise” in the ventilatory and gas exchange responses of children to exercise

“…While only speculative, this assertion is supported by incomplete maturation of ventilatory control mechanisms, such as the peripheral chemoreceptors in children (Springer et al 1988). Others have found evidence for a lower arterial CO 2 partial pressure set-point, (Brady et al 1964;Brady and Ceruti, 1966) causing higher levels of ventilation for a given CO 2 (Cooper et al 1987;Armon et al 1991b;Pianosi and Wolstein 1996;Nagano et al 1998), increased ventilatory sensitivity to CO 2 and greater respiratory responsiveness (Gratas-Delamarche et al 1993) in children compared to adults.…”

Rethinking exercise testing in children: a challenge.

“…However, it is.becoming clear that remarkable differences between children and adults do exist. For example, after I min of exercise on a'constant-power cycle ergometer in the high-intensity range, we found that the recovery time for Veo z was substantially shorter in children (recovery time constant of about 45 s) compared with adults (recovery time constant about 85 s) (22). Similar differences were observed for VE and HR (23).…”

Comportamento cardiorrespiratório em crianças saudáveis durante o exercício progressivo máximo

“…Ohuchi et al 31 demonstrated that the magnitude and change in end-tidal to arterial carbon dioxide tension difference P(ET-a)DCO 2 during graded exercise were smaller, with children showing lower values than adults in both at anaerobic threshold and peak of exercise. We postulate that this finding may be explained by a lower ventilatory efficiency 4,13,[25][26][27] and a lower glycolytic capacity during exercise in children than adults [1][2][3][6][7][8][9] .…”

“…These findings emphasized that the ventilatory pattern in pediatric population is dependent on maturity 2,25-27 . In the same context, Armon et al 27 observed in children higher pulmonary ventilation for a given VCO 2 as compared to adults. What is the explanation for these findings?…”