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Hypercapnic and hypoxic ventilatory responses during growth
Insights
Pediatric hypercapnic ventilatory chemosensitivity decreases with age, correlating with reduced CO2 output. Hypoxic chemosensitivity remained stable across age groups in children aged 7-18.
Area of Science:
- Pediatric respiratory physiology
- Cardiorespiratory control during development
Background:
- Ventilatory chemosensitivity is crucial for maintaining blood gas homeostasis.
- Understanding developmental changes in chemosensitivity is vital for pediatric respiratory health.
Purpose of the Study:
- To investigate age-related changes in hypercapnic and hypoxic ventilatory chemosensitivities in children.
- To correlate ventilatory responses with metabolic parameters during growth.
Main Methods:
- Cross-sectional study of 71 children aged 7-18 years, divided into 6 age groups.
- Hypercapnic response assessed via rebreathing 5% CO2 in O2.
- Hypoxic response measured using isocapnic progressive hypoxia test with controlled end-tidal PCO2.
Main Results:
- Normalized hypercapnic ventilatory response (CO2/BSA) progressively decreased with age.
- This decline paralleled normalized CO2 output (VCO2/BSA) but not O2 intake (VO2/BSA).
- Hypoxic ventilatory chemosensitivities showed no significant age-related differences.
Conclusions:
- Normalized hypercapnic chemosensitivity declines during childhood and adolescence.
- This decrease is associated with reduced CO2 output relative to body mass.
- Hypoxic chemosensitivity appears to be age-independent in this pediatric cohort.
Abstract:
Cross-sectional studies on hypercapnic and hypoxic ventilatory chemosensitivities were performed in 71 children ranging in age from 7 to 18 yrs. The subjects were classified into 6 successive 2-year age groups. CO2 ventilatory response was measured by rebreathing 5% CO2 in O2, a slight modification of the method originally proposed by Read. The results were evaluated when the CO2-ventilation feedback control system was supposed to have attained the open-loop condition. Hypoxic ventilatory response was measured by the isocapnic progressive hypoxia test. To obtain good reproducibility in the ventilatory response, end-tidal PCO2 was maintained at 5 mmHg higher than the resting condition throughout the test. Normalized ventilatory responses to CO2 by body surface area (S/BSA) progressively decreased from the 7-8 through the 11-12 yr groups, and then tended to decrease further in a more gradual manner with increasing age. This trend was very similar to the normalized CO2 output (VCO2/BSA), but did not parallel so closely the normalized O2 intake (VO2/BSA). When ventilatory and metabolic parameters were normalized by body weight (BW), or the lean body mass (LBM), qualitatively similar relationships between CO2 sensitivities and metabolic parameters were also obtained. Contrary to the hypercapnic response, hypoxic ventilatory chemosensitivities were not significantly different among the 6 different age groups. We concluded that normalized hypercapnic chemosensitivity decreased during growth and corresponded well with decreased CO2 output per unit body mass.