Functional Residual Capacity and Sleep States in the Premature Newborn

Abstract

Functional residual capacity (FRC) variations in relation to sleep state changes were studied in 11 premature infants with birth weights of 1.68 ± 0.48 kg and gestational ages of 32.7 ± 2.2 weeks (mean ± SD). Helium dilution was used to measure FRC, and sleep states were identified using neurophysiologic criteria. No significant difference in FRC could be demonstrated between data collected during active sleep (AS) and quiet sleep. However a relationship was shown between AS and paradoxical breathing (p < 0.02) and between AS and irregular breathing (p < 0.05). Several factors are discussed which might explain the discrepancy between the present data in premature infants and the previously published data in term infants. (1) Neurophysiologic identification of sleep states does not include breathing pattern whereas behavioral identification does. It is therefore possible that lung volume changes are related to breathing pattern changes and not to sleep state changes per se. (2) Maturational changes may occur among the mechanisms which control FRC, leading to a progressive stabilisation of FRC, the variation of which could become related to sleep state changes.

Relationship Between Functional Residual Capacity and Oxygen Desaturation During Short Central Apneic Events During Sleep in “Late Preterm” Infants

“…The O 2 -technique can overestimate FRC by about 10% when the tidal volume is low but is highly reproducible (19). Hence, bearing in mind this systematic overestimation, our overall mean FRC value of 31.2 Ϯ 9.6 mL kg Ϫ1 is within the wide range reported in previous studies (using a variety of other methods) of infants of similar ages and body masses (7,23). Part of the difference with previous studies may result from different techniques and populations.…”

“…Although we took care to limit variability, the intrasubject coefficient of variation for FRC was 13.7 Ϯ 11.1%, which corresponds to somewhat lower reproducibility than previously reported with the He technique (8%) (4 ). We failed to observe a sleep state effect on FRC values as previously reported (7,11,23,24), probably because we only measured FRC during regular breathing pattern. In contrast, less recent studies found that the FRC was lower in AS (determined by the behavior and/or from electro-oculograms but without EEG data) (2,10).…”

“…FRC was assessed during regular breathing to analyze the specific sleep state effect and to rule out a possible effect of an irregular breathing pattern on FRC (3,7). A period was scored as regular if the respiratory rate was free of sighing or apneic events and if synchronous chest and abdomen movements were present for the 3 min before and during the FRC measurement.…”

“…Apneas or irregular breathing in the neonate are associated with reduced FRC (7,8). Similarly, a lower FRC is observed if measured within 2 min of an apneic pause (3).…”

“…The higher frequency of apneic events commonly observed in active sleep (AS) may be related to a low FRC (2,10), although a decrease in FRC is not always found in this sleep state (7,11). These conflicting results may be explained not only by various FRC measurement techniques but also because breathing regularity (in addition to the potentially differential effects of sleep state) may have affected the data.…”