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Effect of hypoxia on ventilatory control during exercise in children and adults
C Springer1, T J Barstow, D M Cooper
1Department of Pediatrics, Harbor-UCLA Medical Center, Torrance 90509.
Insights
Children do not show a greater ventilatory response to hypoxia during exercise than adults, despite differences in peripheral chemoreceptor tone maturation. Faster CO2 kinetics in children may explain their quicker ventilatory response at exercise onset.
Area of Science:
- Exercise Physiology
- Respiratory Control
- Human Growth and Development
Background:
- Peripheral chemoreceptor tone (PCT) maturation during growth is not well understood.
- Previous research indicated a greater PCT increase during hypoxic exercise in children versus adults.
- PCT significantly influences the ventilatory (VE) response at exercise onset.
Purpose of the Study:
- To investigate if hypoxia affects the time constant of ventilatory (tau VE) and carbon dioxide (_V_CO2) responses more in children than adults.
- To compare the ventilatory response to hypoxia during exercise between children and adults.
Main Methods:
- Nine children (6-10 years) and nine adults (18-40 years) performed incremental exercise tests.
- Participants breathed normoxic (21% O2) and hypoxic (15% O2) air.
- Ventilatory and gas exchange responses were measured during transitions from rest to exercise.
Main Results:
- Hypoxia accelerated VE responses in both children and adults.
- The magnitude of the hypoxic effect on tau VE did not differ significantly between age groups.
- Children exhibited faster VE kinetics during normoxia, potentially due to storing less CO2.
Conclusions:
- The hypothesis of a greater hypoxic effect on ventilatory kinetics in children was not supported.
- Differences in CO2 storage and other respiratory control mechanisms may explain observed age-related ventilatory responses.
- Further research is needed to elucidate age-specific respiratory control during exercise.
Abstract:
Little is known about maturation of peripheral chemoreceptor tone (PCT) during growth. We recently demonstrated that the increase in PCT was 49% greater during hypoxic (15% O2) exercise in children compared to adults. As the PCT is a major determinant of ventilatory (VE) response at the onset of exercise (measured by the time constant tau), we hypothesized that hypoxia would affect tau VE (and tau VCO2) to a greater extent in children. Nine healthy children (6-10 y old) and nine healthy adults (18-40 y old) performed multiple transitions from rest to constant work rate on the cycle ergometer. Studies were done breathing 21% O2 and 15% O2. Hypoxic breathing quickened the VE responses in all of the adults and children, but the magnitude of the hypoxic effect did not differ between the two groups (in children, tau VE was 50.9 +/- 9.9 s during 21% O2 breathing and 32.6 +/- 6.9 s during hypoxia; in adults, tau VE was 69.4 +/- 17.6 s, which fell to 50.9 +/- 18.4 s during hypoxia). The hypothesized greater ventilatory response to hypoxia in children compared to adults during exercise was not observed. During 21% O2 breathing, the data demonstrated that children stored relatively less CO2 (by 49%) than did adults in the transition between rest and exercise, possibly explaining the faster ventilatory kinetics. We speculate that there must be additional respiratory control differences between adults and children such that for a given increase in PCT-induced by hypoxia, the VE response at the onset of exercise is less in children than in adults.