Faster pulmonary oxygen uptake kinetics in children vs adults due to enhancements in oxygen delivery and extraction

Abstract

This study aimed to examine if the faster pulmonary oxygen uptake (VO2p) phase 2 in children could be explained by increased O2 availability or extraction at the muscle level. For that purpose, O2 availability and extraction were assessed using deoxyhemoglobin (HHb) estimated by near-infrared spectroscopy during moderate-intensity constant load cycling exercise in children and young adults. Eleven prepubertal boys and 12 men volunteered to participate in the study. They performed one maximal graded exercise to determine the power associated with the gas exchange threshold (GET) and four constant load exercises at 90% of GET. VO2p and HHb were continuously monitored. VO2p , HHb, and estimated capillary blood flow (Qcap) kinetics were modelled after a time delay and characterized by the time to achieve 63% of the amplitude (τ) and by mean response time (MRT: time delay + τ), respectively. Mean values of τ for VO2p (P < 0.001), of MRT for HHb (P < 0.01) and of MRT for Qcap (P < 0.001) were significantly shorter in children. Faster VO2p kinetics have been shown in children; these appear due to both faster O2 extraction and delivery kinetics as indicated by faster HHb and Qcap kinetics, respectively.

Oxygen Uptake Kinetics in Youth: Characteristics, Interpretation, and Application

“…response is sensitive to changes in O2 delivery in children. Furthermore, a recent study demonstrated a close matching of the estimated capillary blood flow and pulmonary V  O2 kinetics, both of which were faster in the children than adults(71). These findings may be indicative that the capillary blood flow kinetics limit the pulmonary O2 and PCr kinetics(30,67), while ~85% of the V  O2 slow component has been shown to originate in the contracting muscle(91) and to be associated with the recruitment of less efficient, higher-order type II muscle fibres(34,66).…”

“…given the dependence of phase I on the cardiac output kinetics at the onset of exercise (68,113), and the age-related increase in the cardiac output required for a given pulmonary V  O2 ( On the basis of early studies that reported no differences in the dynamic V  O2 response to moderate intensity exercise between children and adults, it was suggested that the phase II response was fully mature by early childhood and independent of sex. However, more recent, methodologically robust studies re-examining the influence of age have reported contradictory findings, with a faster phase II τ evident in children than adults (43,71). It is likely that this discrepancy is attributable to a failure of earlier studies to utilise well-defined and adequately powered sample populations and to use appropriate modelling and data averaging techniques (7).…”

Sex Differences in Pulmonary Oxygen Uptake Kinetics in Obese Adolescents

“…Leclair et al (10) examined levels of deoxygenated hemoglobin via near-infrared spectroscopy and found that faster O 2 extraction at the onset of exercise occurs in children compared with adults, thus supporting the notion of enhanced muscle oxidative enzyme activity in children (12, 31). To date, no studies have examined potential sex differences in aerobic enzyme profiles in either lean or obese children or adolescents.…”

“…Although there is no support for greater oxygen delivery capacity in adolescents, there is support for enhanced oxidative enzymatic activity (10, 11) in adolescents when compared with adults. Studies that have attempted to provide an explanation of the enhanced muscle enzymatic activity, as well as fiber type distribution, between adults and adolescents have solely focused on normal weight male adolescents (11, 12).…”

Dynamic Interactions of Gas Exchange, Body Mass, and Progressive Exercise in Children

“…Their model assumed a system with first-order linear dynamics, an assumption which is accurate for low-intensity exercise. A number of studies have attempted to determine the value of τ (the time constant for the first-order linear equation) for gas exchange and HR variables in children (7;26). Factors such as maturational status and the presence of disease and obesity appear to play a role (32;39).…”