Baroreceptor reflex sensitivity in human neonates: the effect of postmenstrual age

We performed a cross-sectional study in human infants to determine if indices of R–R interval variability, systolic blood pressure (SBP) variability, and baroreceptor reflex sensitivity change with postmenstrual age (PMA: gestational age + postnatal age). The electrocardiogram, arterial SBP and respiration were recorded in clinically stable infants (PMA, 28–42 weeks) in the quiet sleep state in the first days after birth. (Cross-)spectral analyses of R–R interval series and SBP series were performed to calculate the power of low-frequency (LF, indicating baroreceptor reflex activity, 0.04–0.15 Hz) and high-frequency (HF, indicating parasympathetic activity, individualized between the p-10 and p-90 values of respiratory frequency) fluctuations, and transfer function phase and gain. The mean R–R interval, and LF and HF spectral powers of R–R interval series increased with PMA. The mean SBP increased with PMA, but not the LF and HF spectral powers of SBP series. In the LF range, cross-spectral analysis showed high coherence values (> 0.5) with a consistent negative phase shift between R–R interval and SBP, indicating a 3 s lag in R–R interval changes in relation to SBP. Baroreceptor reflex sensitivity, calculated from LF transfer gain, increased significantly with PMA, from 5 (preterm) to 15 ms mmHg–1 (term). Baroreceptor reflex sensitivity correlated significantly with the (LF and) HF spectral powers of R–R interval series, but not with the LF and HF spectral powers of SBP series. The principal conclusions are that baroreceptor reflex sensitivity and spectral power in R–R interval series increase in parallel with PMA, suggesting a progressive vagal maturation with PMA.