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A developmental study of the dose-response curve of the respiratory sensory reflex
R E Alvaro1, V De Almeida, K Kwiatkowski
1University of Manitoba, Department of Pediatrics, Winnipeg, Canada.
Insights
High carbon dioxide (CO2) inhalation inhibits breathing in preterm infants via an upper airway reflex. This reflex, particularly evident at 8% CO2, was not observed in term infants or adults.
Area of Science:
- Neonatal physiology
- Respiratory control
- Developmental neuroscience
Background:
- Previous studies indicated that high concentrations of carbon dioxide (CO2) inhibit breathing in preterm infants.
- This inhibition is presumed to be mediated by an upper airway sensory reflex.
Purpose of the Study:
- To investigate the developmental aspects of the CO2-induced breathing inhibition reflex.
- To determine the dose-response curve of this reflex in preterm infants, term infants, and adults.
Main Methods:
- A flow-through system and nasal mask were used to administer varying concentrations of CO2 (2%, 4%, 6%, 8%) in oxygen to preterm infants, term infants, and adult subjects.
- Breathing patterns, including apnea and minute ventilation, were monitored during CO2 inhalation.
Main Results:
- Significant breathing inhibition, characterized by apnea, occurred in preterm infants during 8% CO2 inhalation.
- Term infants and adults showed minimal or no breathing inhibition, with shorter pauses observed.
- Minute ventilation decreased significantly in preterm infants at 8% CO2, unlike in term infants and adults.
Conclusions:
- Preterm infants exhibit a distinct upper airway sensory reflex to high CO2 concentrations, leading to breathing inhibition.
- This reflex appears to be developmentally specific, diminishing in term infants and adults.
- The findings highlight developmental differences in respiratory control mechanisms and CO2 sensitivity.
Abstract:
We have shown previously that inhalation of high concentration of CO2 (about 8%) inhibits breathing in preterm infants, presumably through an upper airway sensory reflex. To study the developmental aspects and the dose-response curve of this reflex, we studied eight preterm infants (body weight, 1.6 +/- 0.1 kg mean +/- SE; gestational age, 31 +/- 1 wk; postnatal age, 22 +/- 5 days) and eight term infants (body weight, 3.2 +/- 0.1 kg; gestational age, 39 +/- 1 wk; postnatal age, 8 +/- 6 days) using a flow-through system; eight adult subjects (weight, 67 +/- 5 kg; age, 30 +/- 4 yr) were studied during quiet sleep using a nasal mask. We gave 2, 4, 6, and 8% CO2 in 21+ O2 randomly for 20 to 30 s. A clear inhibition of breathing typically occurred during inhalation of 8% CO2 only in preterm infants, as reflected by the presence of an apnea of 11 +/- 1 s occurring at 7 +/- 2 s after the beginning of CO2 inhalation. Short apneas were occasionally observed with lower concentrations of CO2, but they were significantly fewer and shorter than with 8% CO2. No clear inhibition was observed in term infants or adult subjects, but pauses of 4 and 6 s were observed in the former group and a pause of 7 s was observed in the latter one. The associated changes in minute ventilation during inhalation of 2, 4, and 6% CO2 were not significantly different between the three groups. During inhalation of 8% CO2, minute ventilation decreased only in preterm infants (-26 +/- 10 compared with +32 +/- 10 in term infants and to +17 +/- 5% in adult subjects; p = 0.003 between groups).(ABSTRACT TRUNCATED AT 250 WORDS)