Preterm infants are placed prone in the NICU to improve respiratory function. However, evidence suggests that prone sleeping is associated with impaired heart rate (HR) control, in term and preterm infants after term-corrected age. Currently, the effects of prone sleeping on HR control in preterm infants during their early postnatal weeks in NICU is lacking. We assessed the effects of position and sleep state on HR variability (HRV) as a measures of HR control in preterm infants over the first 3 weeks of life.
Fifty-five preterm infants (24-34 weeks’ gestation) were studied weekly for 3 weeks after birth with cardiorespiratory monitoring. Infants slept for 1 hr in the prone and supine positions and data were analysed in active (AS) and quiet sleep (QS). HRV was assessed by spectral analysis of R-R interval series in low (LF, 0.04-0.15 Hz) and high frequency bands (HF, 0.4-1.5 Hz). HRV LF, HF and total power (TP) and LF/HF were calculated.
Overall, LF, HF and TP were lower prone compared to supine across the first 3 weeks of life (p<0.05 for all), with no interaction between position and postnatal week. R-R interval was shorter in prone compared to supine (p<0.01). LF and TP were lower during QS compared to AS (p<0.001 for both). TP decreased with age, being higher at week 1 compared to week 3 (p<0.05). LF decreased initially, being lower at week 3 compared to week 2 (p<0.05).
The prone position was associated with reduced HRV and higher HR in preterm infants in the NICU. These results suggest dampened autonomic activity in the prone position, which could increase the vulnerability to hypotensive events by limiting the compensatory HR responses. Further studies are required to determine the clinical significance of impaired HRV in the prone position in clinically unstable preterm infants.