Maturational differences in step vs. ramp hypoxic and hypercapnic ventilatory responses

D. Gozal, R. Arens, K. J. Omlin, C. L. Marcus, T. G. Keens

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25 Scopus citations

Abstract

The influence of the speed of stimulus presentation on hypoxic and hypercapnic ventilatory responses (step vs. ramp) is not known. Furthermore, it is unclear whether children and adults respond similarly. We tested ramp ventilatory responses to hypercapnia and hypoxia with use of rebreathing in 8 prepubertal children and 11 adults. We tested step ventilatory responses to hypercapnia with single vital capacity breaths of 15% CO2 in O2 and to hypoxia with five tidal breaths of 100% N2. For children, slopes of step hypercapnic ventilatory responses were always greater than those of ramp responses (0.85 ± 0.07 vs. 0.71 ± 0.07 l · min-1 · Torr end-tidal PCO2-1; P < 0.0005). Conversely, for adults, step responses were always less than ramp responses (0.88 ± 0.19 vs. 2.10 ± 0.29 l · min-1 · Torr end-tidal PCO2-1; P < 0.0007). Similarly, for children, the slopes of step hypoxic ventilatory responses were always greater than those of ramp responses (-0.71 ± 0.09, vs. -0.45 ± 0.04 l · min-1 · Torr O2 saturation-1; P < 0.02), and for adults, step responses were always less than ramp responses (-0.68 ± 0.14 vs. -1.85 ± 0.46 l · min-1 · Torr O2 saturation-1; P < 0.04). We conclude that ventilatory responses vary depending on step vs. ramp presentation of hypercapnia or hypoxia and that the ratio of these responses is reversed in children compared with adults. We speculate that the responsiveness of peripheral chemoreceptors is increased in children compared with adults and that it may play a role in the mechanisms leading to increased ventilatory responses observed during childhood.

Original languageEnglish (US)
Pages (from-to)1968-1975
Number of pages8
JournalJournal of applied physiology
Volume76
Issue number5
DOIs
StatePublished - Jan 1 1994
Externally publishedYes

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Keywords

  • control of breathing
  • peripheral chemoreceptor
  • rebreathing
  • square-wave stimulus

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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