Longitudinal effects of early exposure to intermittent hypoxia on autonomic cardiovascular control in very preterm infants.

Introduction Cardiorespiratory control is immature in infants born preterm compared to those born at term. Animal studies have shown that repetitive hypoxia associated with periodic breathing can alter autonomic control. We aimed to elucidate if the amount of time spent with apnoea and periodic breathing in the neonatal unit was associated with longitudinal changes in autonomic control assessed using heart rate variability. Methods Twenty-nine very preterm infants (10M 19F) were studied during supine daytime sleep on 4 occasions. Study 1: 32-36 weeks post menstrual age (PMA) (n=29), Study 2: 36-40 weeks PMA (n=27), Study 3: 3-months corrected age (CA) (n=20) and Study 4: 6-months CA (n=26). The percentage total sleep time (%TST) spent having apnoeas in active (AS) and quiet sleep (QS) at each study was calculated. Total power, low frequency (LF, sympathetic+parasympathetic activity) high frequency (HF, parasympathetic activity), and LF/HF (sympathovagal balance) were calculated. Infants were divided into two groups based on the %TST spent with apnoeas above and below the median in AS and QS at Study 1. Data were normalised and compared with two-way ANOVA with Bonferroni post-hoc tests. Results When apnoeas were included in the analysis, in QS Total power and HF power were higher, and when apnoeas were excluded HF power was higher in QS but lower in AS in the above median group at Study 4. Conclusion This study provides new evidence that short apnoeas, particularly periodic breathing, which is currently not detected or treated in the neonatal unit can affect autonomic cardiovascular control.