A developmental study of the dose-response curve of the respiratory sensory reflex.
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)