Respiratory variability in preterm and term infants: Effect of sleep state, position and age

The influence of sleep state and position on respiratory variability (RV) was studied in 13 preterm infants (PTIs) and 19 term infants (TIs). Temporally matched epochs of nasal pressure and oxygen saturation (Sp_O2)$(\text{S}{\text{p}}_{{\text{O}}_2})$ data were extracted from nap polysomnography. Inspiratory onset times (I) were determined, and variability measures of the I–I   interval compared in quiet sleep and active sleep, prone and supine and with age. Sleep state influenced respiratory variability (RV) in PTI and TI but Sp_O2$\text{S}{\text{p}}_{{\text{O}}_2}$ only varied with sleep state in PTI (p = 0.03). Position had no effect on RV in TI but influenced the standard deviation of ventilatory frequency (SDf) in PTI (p = 0.04). Age did not influence RV in PTI but SDf and the coefficient of variation of ventilatory frequency (CVf) decreased in TI from birth to 3 months. These data confirm sleep state as the predominant influence on RV in healthy term and convalescent preterm infants, with horizontal prone positioning having little effect when sleep state is controlled for.