Ventilatory response of prepubertal boys and adults to carbon dioxide at rest and during exercise |
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Authors: | A Gratas-Delamarche J Mercier M Ramonatxo J Dassonville C Préfaut |
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Institution: | (1) Service d'Exploration Fonctionelle Respiratoire, Hôpital Aiguelongue, Montpellier, F-34059 Cedex, France;(2) Present address: Laboratoire UFR-STAPS 6, Avenue Gaston Berger, F-35000 Rennes, France;(3) Present address: Laboratoire de Physiologie, Faculté de Médecine, F-35000 Rennes, France |
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Abstract: | Summary 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 (
CO2 = 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 titalPCO2 (P
ETCO2) 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 (
E) andP
ETCO2 above Th; and the slope of the relationship between the quotient of tidal volume (V
T) and inspiration time (t
I) andP
ETCO2 (V
T ·t
I
–1 ·P
ETCO2
–1) values above Th. The
E,V
T, breathing frequency (f
R), oxygen uptake (
O2), and CO2 production (
CO2) 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, onlyV
T ·t
I
–1 ·P
ETCO2
–1 was greater in children than in adults (P<0.001). Third, during exercise, children had a higher SBM (P < 0.02) andV
T ·t
I
–1 ·P
ETCO2
–1 (P<0.001) while Th was lower (P<0.02). Finally, no correlation was found between
E/
CO2 and Th while a significant correlation existed between
E/
CO2 and SBM (adults,r=0.79,P<0.01; children,r=0.73,P<0.05). We conclude that children have, mainly during exercise, a greater sensitivity of the respiratory centres than adult. This greater CO2 sensitivity could partly explain their higher ventilation during exercise, though greater CO2 production probably plays a role at rest. |
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Keywords: | CO2 sensitivity Rest Exercise Children Adults |
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