Author(s): Martin RJ, Carlo WA, Robertson SS, Day WR, Bruce EN
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Abstract The time course of the transient ventilatory response to a sudden change in inspired gas from room air to 4\% CO2 in air was examined in 11 healthy preterm neonates. Changes in minute ventilation (VI), tidal volume (VT), and respiratory frequency (f) were determined over 4 to 5 min of CO2 inhalation during both quiet (QS) and active sleep (AS) in each infant. In both states there was a brisk increase of mean VI in response to 4\% CO2, while mean VT increased more slowly and mean f only increased transiently at 1 to 2 min. Exponential curve fitting to the change in VI and VT for each infant accounted for 64 +/- 20\% of the variance in VI during QS as compared to 30 +/- 18\% during AS (p less than 0.003). In only six infants did exponential curves fitted to the changes in VI and VT during QS reach 90\% of their steady state values within 4 to 5 min of CO2 exposure. Their time to reach 90\% of steady state was always shorter for VI than VT (p less than 0.01). Frequency showed a biphasic response with a transient rise at 1 to 2 min (p less than 0.05) and return to control levels at steady state. These data indicate that not all preterm infants reach a new level of steady state ventilation within 4 to 5 min of 4\% CO2 inhalation. Furthermore, many infants exhibit a biphasic response of f over time which causes VI to reach steady state prior to VT.
This article was published in Pediatr Res
and referenced in Journal of Neonatal Biology