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Maturational differences in step vs. ramp hypoxic and hypercapnic ventilatory responses
1Division of Neonatology and Pediatric Pulmonology, Childrens Hospital Los Angeles, University of Southern California School of Medicine 90027.
Insights
Children and adults show reversed ventilatory responses to hypoxia and hypercapnia depending on stimulus presentation speed (step vs. ramp). This suggests increased peripheral chemoreceptor responsiveness in children.
Area of Science:
- Physiology
- Respiratory Control
- Comparative Physiology
Background:
- Ventilatory responses to hypoxia and hypercapnia are crucial for maintaining blood gas homeostasis.
- The impact of stimulus presentation speed (step vs. ramp) on these responses is not well understood.
- Similarities and differences in ventilatory control between children and adults require further investigation.
Purpose of the Study:
- To investigate the influence of stimulus presentation speed (step vs. ramp) on hypoxic and hypercapnic ventilatory responses.
- To compare these responses between prepubertal children and adults.
- To explore potential age-related differences in chemoreceptor responsiveness.
Main Methods:
- Ramp ventilatory responses to hypercapnia and hypoxia were assessed using rebreathing in 8 children and 11 adults.
- Step ventilatory responses were measured using single breaths of 15% CO2 in O2 (hypercapnia) and five breaths of 100% N2 (hypoxia).
- Slopes of ventilatory responses were calculated and compared between stimulus types and age groups.
Main Results:
- For children, step hypercapnic and hypoxic ventilatory response slopes were significantly greater than ramp responses (P < 0.0005 and P < 0.02, respectively).
- For adults, step responses were significantly less than ramp responses (P < 0.0007 for hypercapnia, P < 0.04 for hypoxia).
- The ratio of step to ramp responses was reversed between children and adults for both hypercapnic and hypoxic challenges.
Conclusions:
- Ventilatory responses to hypercapnia and hypoxia are dependent on the speed of stimulus presentation (step vs. ramp).
- The pattern of these responses is significantly different between children and adults, with children exhibiting a reversed pattern.
- Increased peripheral chemoreceptor responsiveness in children may contribute to the observed differences in ventilatory responses during development.
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.