Unchanged heart rate–respiratory frequency ratio in preterm infants during spontaneous arousals

Abstract

To find out whether a correlation of heart rate (HR) and respiratory frequency (RF) defined as HR-RF-ratio (HRR) may be helpful to identify arousals in term and preterm infants. Polygraphic recordings were performed in 25 term infants (gestational age 40.1 +/- 1.1 weeks) and 25 preterm infants (gestational age 31.1 +/- 1.3 weeks) during undisturbed daytime sleep. Arousals were scored as suggested by the 'International Paediatric Work Group on Arousals' and divided into cortical arousals and subcortical arousals. HRR was defined as HR over RF. Arousals were compared to a 30-sec period preceding an arousals. Two hundred arousals were scored (100 cortical arousals and 100 subcortical arousals). HRR increased during arousals in term infants (p < 0.001). This was true for cortical arousals (p < 0.001) and subcortical arousals (p < 0.05) of term infants. In contrast, in preterm infants HRR remained unchanged during cortical arousals and subcortical arousals. An increase of HRR during arousals is a simple parameter to identify arousals in term infants, but not in preterm infants suggesting that an unchanged HRR might be an indicator of an immature arousal response.